Measurements of Energy

• 1 Calorie = 1000 calories= 1 kilocalories(kcal)= 4.18 kilojoules(kJ)
• 1kcal = energy to raise 1 liter of water 1 degree celcius

Caloric Contents of Macronutrients

(Fuels)

• carbohydrates - 4 kcal/gm
• protein - 4kcal/gm
• fats - 9 kcal/gm
• alcohol -7kcal/gm

Respiratory Quotient (RQ)

• RQ= CO₂ Produced/ O₂ Consumed
• RQ for carbohydrates = 1.0
• RQ for proteins = 0.85
• RQ for fats = 0.7

Types of Carbohydrates

• Monosaccharides - glucose, fructose
• disaccharides - sucrose(table sugar), lactose(milk sugar)
• polysaccharides- starch(plants), glycogen(body stores)
• digestion- enzymes converts polysaccharides into monosaccharides that can be absorbed into blood stream

Essential AA

Conditionally Essential

Amino Acids

• Arginine
• Cysteine
• Glutamine
• Taurine
• Tyrosine^AAA

Nonessential Amino Acids

• Alanine
• Asparagine
• Aspartate
• Glutamate
• Glycine
• Hydroxyproline
• Orinthine
• Proline
• Serine

Nitrogen Balance

• Nitrogen balance = (gm protein in per day/6.25) - (TUN+2)
• goal is +2 to +4 gm N balance per day
• Total Urine Nitrogen(TUN) is measured
• if you go into the negatives it means you are breaking down proteins
• most have to estimate total urine nitrogen

Classification of Fatty Acids

• length: short chain(less then 6 carbons), medium chain(6-10 carbons), long chain(12 or more carbons)
• number of bonds: saturated FA (no double bonds), monounsaturated FA(single double bond), polyunsaturated FA(multiple double bonds)
• Essential vs non-essential FA

Saturated Fatty Acids

• butter, dairy products, meats, ect
• solid at room temperature
• increases LDL (bad cholesterol
• recommended consume less then 10% of total Calories per day as saturated fatty acids
• no double bonds

Unsaturated Fatty Acids

• Vegetable oils(corn oil, peanut oil, olive oil)
• poly unsaturated FA liquid at room temperature
• mono-unsaturated FA have lowest cholesteral levels and are the healthiest FA
• increases HDL (good cholesterol
• recommend to consume no more than 30% of total calories/day as unsatureated FA

Trans Fats

• artificial unsaturated fat containing trans-isomer FA
• increases LDL(bad cholesterol
• recommend takin in less than 20 Calories (about 2 grams) trans fats per day

Digestion and Absorbtion of Fats

• pancreatic lipase enzymes convert fats in the diet to free FA and 2-monoacylglycerols
• bile salts secreted into the bowel from the gallbladder
• these form micelles in the lumen of the bowel that are absorbed through the intestinal mucosa
• Free FA and 2 monoacylglycerols are then utilized by liver and excess is converted back into triacylglycerols which are transported by two lipoproteins(chylomicrons and VLDL) to adipose tissue where it is stored

Roles of Fats in the Body

• Energy-through β oxidation of FA, ketone bodies are formed that can be used as energy source for most tissues throughout the body
• structure- integral part of the structure of many of the cells of the body especially cell membranes
• function-carriers of essential fatty acids and fat-soluble vitamins; certain FA precursors of prostaglandins and other eicosanoids taht serve important metabolic functions throughout the body

Micronutrients

• vitamins: water soluble(C, thiaminem riboflavin, folate, B6, biotin) and fat soluble(A, D, E, K)
• electrolytes- sodium, potassium, chloride
• minerals- calcium, magnesium, phosphorous, iron
• trace elements - iodine, selenium, copper, zinc, sulfur, manganese, floride, chromium, molybdenum

Basal Energy Expenditure or

Basal MEtabolic rate

• mentally and bodily at rest, thermoneutral environment, 12-18 hours fasting
• formulas available to calculate BMR or aprox 24 kcal/kg/day or 1kcal/Kg/hour (for young adults of ideal body weight
• BMR increases from male gender, increased body weight, colder climates, fever, hyperthyroidism, pregnancy/lactation, younger age, genetic factors

Total Daily Expenditure or

Daily Energy Expenditure

• basal energy expenditure or basal metabolic rate
• resting energy expenditure or resting metabolic rate
• diet-induced thermogenesis
• energy expenditure due to physical activity 

Harris-Benedict Equation

• Calculates basal metabolic rate with weight in pounds, height in inches and age in years (different for men and women)
• then multiply based on numbers that coincide with amount of exercise

Ireton-Jones Energy Equations

(IJEE)

• dependent on ventilator

Nutritional States of the body

• fed state (stimul. release of insulin and inhibits release of glucagon in pancreas)
• early fasting state (after 12 hours, decreasing serum glucose stimulate glucagon levels)
• starvation adapted state (3-5 days of fasting 
• hypermetabolic state (fight or flight state, mostly protein, doesnt use much fat)

Body Mass Index (BMI)

• BMI= Weight(kg)/Height (m²)
• categorization of body habitus
• malnutrition - BMI < 18.5
• Normal - BMI 18.5 - 25
• Overweight - BMI 25-30
• Obesity - BMI 30-40
• Morbid Obesity - BMI > or equal to 40

Scope of Problem of Obesity 

• incidence: over one third of US pop is obese, 5% morbidly obese, 17%  of children and adolescents are obese
• 400,000 die anually from obesity related comorbidities
• 147 billion medical costs associated with obesity

Metabolic Pathways

• gluconeogenesis, sythesis of glucose
• glycolysis, conversion of glucose to acetyl-CoA
• nucleotide synthesis, energy co-factors, RNA, DNA synthesis
• nucleotide degradation, uric acid
• cholesterol degradation, bile acids for vitamin absorption
• cholesterol synthesis, steroid synthesis

Metabolic Intermediates

• normally have no function other than to connect the different pathways
• certain intermediates have key roles in regulating metabolic pathways
• citric acid produced by TCA cycle used in fatty acid synthesis regulates glycolysis
• acetyl CoA produced from glucose is used for fatty acid, and ketone body formation regulates gluconeogenesis

Scurvy

• vitamin C defficiency 
• defective collagen formation leading to subcutaneous hemorrhage, aching bones, joints and muscle in adults
• rigid positiona nd pain in infants
• common food sources are citrus fruits, potatoes, peppers, bcroccoli, spinach, strawberries

Beriberi

• thiamin defeciency
• edema, anorexia, weight loss, decrease in short term memory, confusion, muscle weakness and enlarged heart
• food sources enriched cereals and breads, unrefined grains, pork, legumes, seeds and nuts

Ariboflavinosis

• riboflavin deficiency
• sore throat, hyperemia, edema of oral mucosal mem, cheilosis, glossitis, magenta tongue
• common food sources are dairy products, meats, poultry, fish, legumes

Pellagra

• niacin defficiency
• pgimented rash in areas exposed to sunlight, vomiting, constipation or diarrhea, bright red tongue, neurological symptoms
• sources are chicken, beef, fish, enriched cereals or whole grains, most foods

Megaloblastic anemia

• folate deficiency
• citrus fruits, dark green vegetables, fortified cereals and breads legumes

Sporadic Mutation

• caused by chemicals, malfunction of dna replication or repair systems
• increases with genome size and certain nucleotide sequences
• GC(mutation hotspots)(80% of CG dinucleotides are methylated
• transistion (purine to purine or pyr to pyr)
• transversion(purine for pyr or pyr to purine)

Missense Mutation

• synonymous(point mutation does not change amino acid)
• non-synonymous(point mutation changes amino acid)

Haplo-insufficiency

Allosteric Enzyme Regulation

• modulate overal metabolic needs of a cell
• allosteric activators shift v vs substrate curve to left, while allosteric inhibitors shift curve to right
• vmax and km changes
• bind to sites other then catalytic site
• most key regulator enzymes of major pathway are allosteric

Criteria for using a screen test

• significat burden of corresponding disease in the population
• preclinical stage of the corresponding disease is detectable and prevalent
• early detection improves mortality and can be accomplished without significant morbidity
• effective treatment available for the detected condition

Test Result Interpretations

• Positive predictive value (a/a+c) x 100
• negative predictive value (d/b+d) x100
• sensitivity (a/a+b) x 100 when someone does have the disease how often do they have a positive result
• specificity (d/c+d)x 100 when someone doesnt have the disease how often do they have a negative result

Characteristics of an Ideal

Screening Test

• widely accessible 
• simple to administer
• inexpensive
• associated with minimal discomfort and morbidity
• results must be valid and reproducible
• must be able to detect the preclinical phase 

Diabetes Mellitus

• group of metabolic disorders characterized by an elevated blood glucose and its consequences
• type 1 onset is abrubt and type 2 insidious 
• type 2 people are obese
• type 1 has autoantibodies (insulin, GAD2)
• type 1 has 50% twin concordance, and type 2 90%

Reasons to order laboratory testing

• screen for disease in asymptomatic patients
• establish a diagnosis in asymptomatic patients
• monitor therapy(either benefits or side effects)
• provide prognostic information or refine a diagnosis
• confirm that the individual has recovered from or is free of disease

Action of Metformin

• activates glucose uptake in muscles (includes AMPK)
• activates pathway in liver that decreases gene expression of lipogenic enzymes and increases insulin sensitivity
• increases fatty acid oxidation in liver
• lowers fatty liver 

Latent Autoimmune Diabetes of Adults

(LADA, DM type 1.5)

• same pathogenic mechanism as type 1 diabetes, seems to progress more slowly
• positive autoantibodies and low endogenous insulin
• some suggest that up to 10% of patients with type 2 diabetes are actually LADA
• treat patients with insulin

Four Basic GI Processes

• motility-pass food stuff/chyme along tract, mix
• secretion-enzymes, biological detergents/ions provide optimized env. for digestion/absorption
• digestion-physical/chemical modifications of food so absorption can occur
• absorption-nutrients/H₂O/ions 

Salivary Glands

• secrete saliva/mucous vital to initial breakdown of food
• parotid-serous secretion(amylase)
• sublingual/submandibular-serous/mucous (provides lubrication for esophagus) 

Insulin

• functions through tyrosine kinase receptor
• increases cellular glucose uptake in muscle and adipose, glycogen syn in liver and muscle, protein syn in liver and muscle, and FA and trigly in liver and adipose
• decreases gluconeogenesis in liver, glycogenolysis in liver and muscle, ketogenesis in liver, lipolysis in adipose, proteolysis in muscle
• IRS1 inudces SREBP induction of lipogensis while IRST phosphyr and inactivates FOXO 
• influences these pathways through  PIP/Protein Kinase B(AKT)

Glucagon

• activates glucagon receptor coupled to G_as increasing cAMP levels
• increases: glycogenolysis in liver(no glucagon receptors in muscle), gluconeogenesis in liver, ketogenesis in liver(only organ ketogenesis) and lipolysis in adipose 

Epinephrine(adrenaline)

• Beta adrenergic  coupled to G_as and alpha will stimulate G_aq 
• Beta causes increase of cAMP
• increases glycogenolysis in liver and muscle and lipolysis in adipose tissue

Cortisol

• activated glucocorticoid receptors to increase gene transcription
• increases gluconeogenesis in liver, glucogen synthesis in liver and proteolysis in muscle
• decreases tussue glucose utilization in liver, muscle and adipose
• Adrenocorticotropic Hormone(ACTH) is released from pituitary and stimulates the release of cortisol from adrenal cortex

Insulin Synthesis

• synthesized in ER as a preprohormone
• pre sequence is cleaved for secretion into lumen
• proinsulin is converted to insulin by proteolytic cleav.
• glucose enters βcells via a glucose transporter for ATP syn
• ATP inhibits k+ channels, leading to a membrane depolarization, which activates a voltage gated Ca2+ channel
• Increased Ca2+ stimulates the fusion of insulin vesicles with plasma membrane
• threshold for insulin release is about 80mg/dL

Stimulation and Inhibition

of Insulin Release

• glucose and amino acids stimulate insulin release 
• neural signals coordinate insulin release with the secretory signals initiated by the ingestion of fuels
• gastric inhibitory peptide(GIP) and glucagon like peptide 1(GLP-1) and GLP2 aid in insulin release
• epinephrine secreted in response to fastingm stress, and exercise decrease te release of insulin, signaling energy utilization

Synthesis and Secretion of Glucagon

• glucagon is a peptide hormone synthesized in α cells by cleavage of a larger prepoglucagon and glucagon containing GLP-1 and GLP-2
• glucagon is rapidly mobilized in liver and kidneys, half life of 3-5 min
• glucose and insulin inhibit glucagon release
• cortisol, neural sress and epinephrine stimulate glucagon release
• amino acids also stimulate glucagon release

Adrenergic Receptor

• β-adrenergic receptors: g protein-coupled receptor, Gs, which activates adenylate cyclase/cAMP/PKA signaling
• β1-heart, muscle contraction, norepinephrine
• β2-liver, skeletal muscle and other tissues, mobilization of fuel(glycogen); epinephrine increases release of insulin and glucagon
• β3- adipose tissue, mobilization of triglycerides, thermogenesis
• α1-adrenergic receptor: vascular and smooth muscle contraction: activates PIP2-Ca2+ signaling; also activates glycogenolysis in liver

Mitochondrial Nuclear Encoded Proteins 

• coded in unfolded form
• hsp70 matrix protein transports nuclear encoded proteins to mitochondria
• transported into mitochondria via proteins made in mitochondria (nuclear protein usually has positive charge and receptor negative charge)
• protein insert into intermembrane space via TOM complex channel
• inserted into matrix by TIM complex(might use ATP)
• hsp60 in matrix then mediates folding and matrix proccessing protease(mpp) cleaves into mature protein (also uses ATP)

Change in Free Energy ΔG

• ΔG⁰ is the change of gibbs free energy at pH7.0, 25C under standard state
• positive ΔG⁰ -endergonic, requires energy input
• Negative ΔG⁰  releases energy; thermodynamically favorable reaction under the standard state
• high energy phosphate bond of ATP- ΔG⁰ = -7.3Kcal/mole

Mechanical Work: Muscle Contraction

• myosin ATPase: hydrplysis of ATP to provide energy for muscle contraction (ATP binds to move head away from actin, hydrolysis, when Pi leaves head powerstrokes)
• kinesins ATPase: hydrolysis of ATP to provide nergy for moving along microtubule, which is important for several cellular functions, including mitosis and meiosis 

Energetics of glycogen synthesis

• to synthesize the glycogen, energy is provided the cleavage of 3 high-energy phosphate bonds: ATP hydrolysis, UTP hydrolysis and pyrophosphate
• energy transfer is facilitated by phosphoryl group transfer and formation of activated intermediate, UDP-glucose
• the converson of G6P to G1P has a positive ΔG and is pulled by accumulation of substate and removal of the product
• high energy phosphate bound of UTP is cleaved to form activated sugar, this reaction is further facilitated by pyrophosphate hydrolysis
• cleaved of bond btw UDP and glucose provides energy for attaching glucose to glycogen 

Thermogenesis

• energy used for generation of heat
• energy from oxidation of a fuel= heat release+ work performed + increase in order of molecules
• shivering thermogenesis(increase ATP utilization, fuel oxidation and release of energy as heat)
• non-shivering thermogenesis (adaptive thermogenesis, controlled by UCP; energy of fuel oxidation to ATP decreased)

Redox Potential

• provides a measure(in volts) of a molecules tendency to release or accept electron
• oxygen, the best electron acceptor, has the largest positive reduction potential and the most willing to accept electron
• the transfer of electrons froma ll compounds to O₂ is energetically favorable and occurs with release of energy
• the more negative the reduction potential of a compound, the greater the energy available for ATP generation when the compound passes its electrons to oxygen

Oxygenase and Oxidase

• not involved in ATP generation
• Oxidase transfers electrons from the substrates to O₂ to reduce to water or H₂O₂ 
• oxygenase incorporate one or both of the atoms of O₂ into the organic substrate
• a metal can take an oxygen, forming an oxygen reactive oxygen complex

Hypoxia Conditions

• decreased ETC activity
• decreased ATP and adenine nucleotides
• increased Na (Na/K pumps no longer working from lack of ATP)
• cellular swelling
• increased Ca2+
• increased H+ because no longer Na gradient for antitransporter to work

Coenzyme FAD

• can accept single electron, and electron transfer independently from 2 different H atoms
• Participate in double bond formation(succinate to fumarate) or disulfide bond formation9lipoate to lipoate disulfide in the α-KG dehydrogenase reaction
• FAD normally remains covalently attached to an enzyme
• FAD is FMN and AMP

Coenzyme NAD

• NAD+ accepts a pair of e as the hydride ion(H-). Nicotinamide ring accepts H- from the C-H bond
• participate in the oxidation of alcohol to ketone or ketone to acid
• NAD+ and NADH are more like substrate and product than coenzyme
• ration of NADH/NAD+ regulate TCA cycle, coordination fuel oxidation rate to the rate of ATP use
• reactions catalyzed by isocitrate dehydrogenase 

Succinate Dehydrogenase

• catalyzes the reaction of succinate to fumarate
• attached to the inner mitochondrial membrane
• has attached to it Fe-S which has His-FAD attached to it (transfer of e-)
• rx yeilds fumarate and FADH2

Role of CoA(Coenzyme A)

in the TCA 

• sulfur does not share electrons with carbonyl group
• unlike oxygen enters bond, no resonance structure for thioester bond (not stable) 
• acetyl CoA to citrate(citrate synthase)
• succinyl CoA to succinate and CoASH (makes GTP)

α-ketoacid dehyrogenase complexs

• other members are pyruvate dhase complex, and branched-chain amino acid α-keto dhase (related to maple syrup urine disease
• FADH2+NAD+ -> FAD + NADH + H+ ΔE= -0.101V is an energetically unfavorable reaction
• since FAD is covalently bound to enzyme, the side chain of amino acid can modify the E^o' value, thus the transfer of e- from bound FAD to NAD+ in dihydrolipoyl DH is energetically favorable

Thiamine Pyrophosphate(TPP) in the 

α-ketoglutarate dhydrogenase complex

• thiamine deficency results in heart failure(referred to as beriberi heart). heart muscle, skeletal muscle, and nervous tissue present with the most obvious signs of thiamine deficiency
• thiamine deficiency is most often associated with alcoholism in western societies

Positive Reactions in TCA cycle

• these reactions are positive, and unfavorable(favor the substrate)
• Malate -> oxaloacetate(+7.1kcal)
• Citrate to Isocitrate(+1.5kcal)

Malate and Citrate

• both found in TCA cycle and are substrates in unfavorable reactions
• during fasting malate can be used for gluconeogenesis
• citrate can go to cytosol and be converted to Acetyl-CoA by cytosol lyase, this can then be used in FA and cholesterol Biosynthesis
• in liver, NADH/NAD+ ratio determines if acetyl CoA goes to TCA cycle or ketone body synthesis

Regulation of Citrate Synthase

• no allosteric regulator 
• activated by[oxaloacetate]
• inhibited by citrate(product inhibition)

Allosteric Regulation of Isocitrate Dhase

• at physiological concentrations of isocitrate(0.1mM), ICDH is inactivated
• ADP shifts the curve to the left, so that ISDH is activated NADH inhibits activity
• Ca²⁺ stimulates activity, synchronizes with muscle contraction 

Regulation of α-ketoglutarate Dhase

• non-allosteric regulator
• NADH and succinyl CoA inhibit activity(product inhibition)
• Ca²⁺ stimulates activity

Regulation of TCA cycle intermediates

• ensures NADH is generated fast enough to maintain ATP homeostasis
• regulate concentration of TCA cycle intermediates
• decrease rate of ICDH -> increase citrate -> stimulate citrate efflux to cytosol 

Sources of Acetyl CoA

• fatty acid, palmitate
• ketone body, acetoacetate
• pyruvate (formed from sugar glucose and amino acid alanine)
• ethanol

Pyruvate Dehydrogenase Complex

• links glycolysis and TCA cycle
• pyruvate decarboxylase(E1, α, β)(TPP), transacetylase(lipoate, CoA)(E2), and dihydrolipoyl dhase(FAD, NAD)(E3)
• convert pyruvate to acetyl CoA
• deficiences of PDC complex are most common inherited diseases leading to lactic acidemia and similar to pyuruvate carboxylase deficiency(leigh disease)
• most common PDC genetic defects are in the gene for the α subunit of E1 (E1 gene is X linked)
• target of arsenic poison(arsenate and arsenite)
• NADH and CO2 is released when pyruvate to Acetyl CoA

Regulation of Pyruvate Dehydrogenase

Complex

(inhibition)

Regulation of Pyruvae Dhase Complex

(Activators)

• ADP: dephosphorylation of E1 by phosphatase
• CoA
• NAD
• Rapid ATP utilization keeps PDC active
• PDC phosphatase requireds Ca2+ for full activity, more Ca2+, less phosphorylated E1 subunits, more activity

TCA Intermediates and Biosynthesis Pathways

• oxaloacetate->amino acid synthesis(aspartate)
• malate ->gluconeogenesis
• succinyl CoA -> Heme synthesis(bone marrow)
• α-Ketoglutarate->amino acid synthesis(glutamate) or Neurotransmitters(brain, GABA)
• Citrate-> tatty acid synthesis

Anaplerotic Reactions

• pathways that replenish the intermediates of the TCA cycle
• amino acid degradation forms TCA cycle intermediate
• pyruvate carboxylase is a major anaplerotic enzyme
• pathway essential for neuronal survival in brain(PC is present in astrocyte and uses TCA inter. to syn glutamate
• in liver, cells depend on PC for an anaplerotic supply of OAA for gluconeogenesis(due to low OAA levels)

Overview of Oxidative Phosphorylation

• Complex 1(NADH): oxidoreductase
• Complex II CoQ(FADH2)
• Complex III (cytochrome b-c1 complex
• cytochrome c
• complex IV: cytochrome oxidase(2H+1/2 ->H2O)
• electrochemical potential drives ATPM synthaseelectrochemical potential is 0.15-.2V and pH of 0.75

ATP Synthase Motor Rotation

• glutamyl carboxyl group of c-subunit accept a H+
• C subunit rotates into membrane
• rotation exposes a H+ containing C=subunit to the matrix side
• rotation is completed by attraction btw C-subunit glutamyl group and a subunit arginyl group

Respiratory Chain inhibition

• in absence of O2 there is no ATP synthesis from oxidative phosph.
• site-specific inhibitors of ETC block flow of electrons, prevent Δp formation and inhibit ATP synthesis
• complex I inhibitor: rotenone, amytal
• complex II inhibitor: malonate(comp. inh of succinate dhase)
• Complex II inhibitor: Antimycin A
• Complex IV inhibitors: CN-, CO
• 
  

Cyanide Poisoning

• it binds to the oxygen binding site of Complex 4
• oxygen usually gets converted to H2O at complex IV
• CN-
• treatment: CN- +S2O3 --rhodanase--> SO3 + SCN-
• Treatment: Administration of high concentration O2 and methylene blue

Oxphos Disease

• clinical diseases involved in the components of oxidative phosphorylation
• the most common encounted degenerated diseases
• mutation in mitochondrial DNA (circular DNA, 16,659 bp)
• phenotype is product of severerity of defect, degree of heteroplasmy and the relative depenence of each organ system on mitochondrial energy production

Genetic char. of Mitochondrial DNA

• mtDNA is semiautonomous, consistant with its endosymbiotic origin
• mtDNA undergoes replicated segragation up cell division(mitosis and meiosis)
• mutant mtDNA can either be heteroplasmy or homoplasmy
• mtDNA expression is dependent on the tissue energy threshold
• mtDNA has a high mutation rate: 10-20fold more evolution and far more prone to deleterious mutations (naked DNA, no histones, lack of efficient repair system
• efficiency of ETC and oxphos declines with age(proportion of mutats in cells increases with age due to oxygen free radical damage

Heteroplasmy and homoplasmy

• mitochondrial DNA(mtDNA) undergoes replicative segregation upon cell division
• heteroplasmy: a cell harbors both mutant and normal mtDNAs
• homoplasmy: heterplasmic mtDNA is randomly distributed to daughter cells, and the proportion of mutant mtDNA can drift toward predominantly mutant or wild type mtDNA over time

Mitochondrial Myopathy

• mitochondrial dysfunction causes mitochondrial morphology changes, ragged red fibers(RFF) in muscle and accumulation of abnormal mitochondral aggregates
• one type is mitochondrial encephalomyopathy
• clinical symptoms: increase in serum lactate during and after exercise and congenital lactic acidosis, increase in abnormal organic acids in urine, increase in carnitine esters in the urine, decrease in serum free carnitine, abnormal muscle morphology(RFF, accumulation of abn mit aggregates

Mitochondrial Encephalomyopathy

• heterogeneous, multisystem disorders including muscle, liver, brain and kidney
• Kearns-Sayre Syndrome(KSS): caused by duplication mutations and deletion mutations 
• Myocionus epilepsy with RRF(MERRF) caused be tRNA^lys mutation
• (MELAS)Mitochondrial encephalopathy, myopathy, lactic acidosis and stroke like episodes: 80-90% mutations in tRNA^leu

Mitochondrial DNA Mutations

and Diseases

• missense mutation: a single point mutation in the mRNA coding gene caused by the substition of a conseved amino acid in the oxphos component
• protein synthesis mutation: a single nucleotide subs in the tRNA genes of mtDNA causes mitochondrial protein syn deficiency
• insertion-deletion mutations: most patients have a single mtDNA deletion, but the size and position differ among patients. majority of mtDNA deletion cases are spontaneous with no family history. diseases associated with mtDNA deletions progress with age

AZT

• aids treatment (Ivy Sharers case)
• can result in adverse effects of severe mitochondrial myopathy, including RRF accumulation with skeletal muscle cells
• since AZT can act as an inhibitor of mtDNA polymerase, leading to a depletion of mtDNA in cells and a disorder of oxidative phosphorylation
• however the drug induced disorder is reversible

Doxorubicin

• highly effective anticancer agent(chemotherapy)
• limited by a specific, cumulative, dose dependent cardiotoxicity
• bind cardiolipin, inhibits succinate oxidation, inactivates cytochrome c oxidase, interacts with CoQ and inhibits ATP synthase, which decrease oxidative phosphorylation and increase oxygen free radical production, leading to adverse effect of heart failure

Aspirin Overdose

• salicylate poison->uncoupled mitochondria -> ATP declined and AMP increased in cell -> stimulate glycolysis pathway -> increase lactic acid -> metabolic acidosis
• can also increase pulmonary ventilation which increases output of CO2 causing respiratory alkolosis?

Digestion of Dietary Carbohydrates

• dietary carbs constitute 50% of the calories in the average US diet
• starch is the storage form of carbohydrates(glucose linked by α1,4 and  α1,6 glycosidic bonds)
• in pancreatitis, serum  α-amylase increases
• under lactase deficiency, lactose is metabolized by bacteria(causes bloating, abdominal cramps and diarrhea)
• indigestible polysaccharides(cellulose) of the dietary fiber are excreted to feces

Absorption of Dietary Carbohydrates

• glucose and galactose enter enterocytes via Na-glucose cotransporters 
• Glucose can also enter via GLUT2 and fructose can enter via GLUT5
• on basolateral side glucose and galactose are transported to blood via GLUT2 and fructose via GLUT5

GLUT1

• human erythrocyte, blood-brain barrier, blood retinal barrier, blood placental barrier and blood testis barrier
• expressed in cell types with barrier functions
• a high affinity(low km) glucose transport system

GLUT2

• found in liver, kidney, pancreatic βcells, and serousal surface of intestinal mucosa cells
• a high capacity, low affinity(high km) transporter
• may be used as the glucose sensor in the pancreas

GLUT3

• Brain(neurons)
• major transporter int he CNS
• high affinity system(low km)

GLUT4

• found in adipose tissue and skeletal and heart muscle
• only insulin sensitive transporter
• in presense of insulin, the number of GLUT4 transporters increases on the cell surface
• high affinity system(low km)

GLUT5

• intestinal epithelium and spermatazoa
• this is actually a fructose transporter

Lactose Intolerance

• pain, nausea and flatulence after ingestion of foods containing lactose(dairy products
• caused by a primary deficiency of lactase production in small intestine or secondary to an injury to the intestinal mucosa
• bacteria break down the lactose making methan gase and lactic acid that has osmotic affect increasing fluid load
• this increase in fluid load leads to increase in peristalsis and a malabsorption of fats, proteins and drugs

Anaerobic Glycolisis

• pyruvate is used to form lactate rather then acetyl-CoA
• production of lactate causes lactic acidosis

Biosynthesis of Triglycerides and 

Non-Essential Amino Acids

• Glucose can be converted to serine, pyruvate or glycerol-P
• serine can be used to make glycine or cysteine
• pyruvate can make alanine, OAA or acetyl CoA
• Acetyle CoA can either enter TCA cycle or Make FA that is used with glycerol for Triglyceride formation
• OAA can be converted to Aspartate
• Glutamate and other AA can be made from TCA cycle

Fates of UDP-Glucose

• synthesized from G1P
• can go to glycoproteins/glycolipids/proteoglycans, UDP-Glucuronate, glycogen, and UDP-glalactose
• UDP galactose can form lactose by taking out lactose
• UDP glucuronate can form glucuronides or the three glyco things.

Oxphos enzyme degenerative Diseases

• oxophos capacity declines with age and its mech are oxidative damage to mt DNA deletions, enrichment of deleted mtDNA replicative advantage and progression of disease with aging
• common degenerative diseases are: ischemic heart disease, dilated and hypertrophic cardiomyopathy, parkinsons disease, alzheimers disease, huntingtons disease and maturity onset diabetes(type 2)
• all associated with oxphos enzyme defects, involve those tissues most reliant on mitochondrial energy(cns, skel, heart, kdiney), have complex genetics in which multiple nDNA or mtDNA(spontaneous) can give similar phenotypes, and frequently expressd later in life

Apoptosis(mitochondria)

• mitochondria play a key role in initiating apoptosis
• related to cytochrome C that is losely associated w/  inner membrane
• when energy is low and Reactive oxygen species(ROS) is high then mtPTP becomes activated
• reactive oxygen species: mitochondrial combustion-> oxygen radical
• this leads to cell death(apoptosis) by the mtPTP opening pore allowing cytochrome c to flow into the cytosol, initiating apoptosis (activates Apaf-1 which activates caspases)

Coupling of Electron Transport and 

ATP synthesis

• As ADP level increases, Proton influx(thru ATPase) increases
• this leads to a decrease in the electrochemical gradient(Δp) and an increase in proton pumping and electron transfer to maintain the gradient
• this leads to an increase in oxygen consumption(at complex 4)
• this happens during exercise and the opposite during rest(which causes a NADH and FADH2 build up and a decrease in TCA cycle)

Uncoupling ATP synthesis 

From ETC

• uncopulers are ionophores that bind and carry H, K, or Na and prevent formation of H gradient and or membrane potential, thus inhibiting oxidative phosphorylation
• ETC however is stimulated due to uncoupling and oxidative phosphorylation
• electron flow and proton pumping attempt to maintain the electrochemical gradient
• results in increased oxygen consumption and heat production but no ATP synthesis
• Dinitrophenol(DNP) is lipid soluble and can diffuse acrose the membrane(a proton ionophore)(brings protons back into matrix)

Ionophores

• bind and carry H, K, or Na and prevent formation of H gradient and or membrane potential, thus inhibiting oxidative phosphorylation
• DNP is one that carries H back to matrix
• Caronyl cyanine is an FCCP, proton ionophore
• nigericin(K-H antiportor) functions to collapse ΔpH
• Valinomycin (potassium ionophore) functions to collapse Δψ
• Δp=ΔpH+Δψ

Uncoupling Proteins and Thermogenesis

• chemical uncoupling mediated by UCP(proton conduction channel to short circuit ATPase)(thermogenin)
• increases oxygen consumption to produce heat
• UCP1 in brown adipose(nonshivering thermogenesis), UCP2 in most cells, UCP3 in skeletal muscle, UCP4/5 in brain
• cold stimulates hypothalmus which stim Symp NS and NE release
• NE activates β3 adrenergic receptors which activate adenylate cyclase(enhances lipolyses and thermogenesis in skeletal muscle)

Phosphorylation inhibitors

• oligomycin is an ATPase inhibitor that blocks electron flow through F₁ATPase(blocks flow of H back to mit) and inhibits ATP synthesis; ETC is also inhibitied because ETC is coupled to oxidative phosphorylation
• Altractylate: found in mediteranean plants and inhibit cytosol ADP to bind to ATP-ADP translocase
• bongkrekate: found in SE Asian bamboo and inhibit ATP binding to translocase in mit. matrix(very toxic)

Adenine Nucleotide Transporter

(ANT)

• found on inner mitochondrial membrane
• is a type of antiporter that moves ATP out of the matrix and ADP into the matrix

Inner Mitochondrial membrane Transporters

• ANT
• Phosphate-H symporter (bringing in to matrix)
• Pyruvate-H symporter(bringing in to matrix)
• Ca Uniporter that is driven by membrane potential

Voltage-Dependent Anion Channel

(VDAC)

• found on outer mitochondrial membrane
• hexokinase binds to VDAC and enables utilization of newly synthesized ATP in glycolysis
• pyruvate flows through channel into intermembrane space
• citrate flows out of mitochondria
• ATP flows out and ADP in
• BAX is a pro-apoptotic channel protein and BCL-2 is anti-apoptotic protein on VDAC (calcium overloading cause MPTP pore opening)

Salivary and Pancreatic α-Amylase

• an endoglycosidase, randomly cleave internal α1,4 bonds btw glucosyl residues and generate disaccharides, trisaccharides and oligosaccharides
• disaccharides-maltose, isomaltose
• oligosaccharides-limit dextrins
• α-dextrins-with α-1,6-branches

Metabolism of Sugars by Colonic BActeria

Lactose Intolerance

• lactase: a β-glycosidase, hydrolyzes β-1,4 bond connecting galactose and glucose
• highest lactase activity in infant and reduced in adults (10% of before)
• congenital lactase deficiency is autosomal recessive
• secondary lactase deficiency: intestinal injury-kwashiorkorm colitis, gastroenteritis, alcohol

Dietary Fiber

• polysaccharide derivatives and lignan
• insoluble fiber: cellulose, hemicellulose, lignin
• soluble fiber: pectins, gums, mucilages
• human enzymes cannot digest fiber
• bacterial flora in the gut may metabolize soluble fiber to gases and short chain fatty acids

Glucose Transporters

• GLUT1: high affinity glucose transporter in red blood cell, blood-brain barrier(1-7mM)
• GLUT2: liver-high capacity, low affinity transporter(15mM)
• GLUT3: Brain, high affinity transporter
• GLUT4: adipocyte, muscle; insulin-sensitive
• GLUT5: intestinal epithelium; a fructose transporter

Hypoglycemia

• a response to low blood glucose(1 to 3mM)
• light headedness, dizziness and even coma

Fructose Metabolism

• principally in liver and to a lesser extent in the SI mucosa and proximal ep. of the renal tubule
• fructokinase hydrolyzes ATP to form Fructose-1-P from fructose
• aldolase B(liver) cleaves F-1-P to Dihydroxyacetone-P(DHAP) and glyceraldehyde
• aldolase B is the rate limiting enzyme in fructose metaolism because low affinity for F-1-P compared to glycolysis interm. F-1,6-bis-P
• triose kinase can then hydrolyze ATP to convert glyceraldehyd to Glyceraldehyd-3-P(an interm. of Glycolysis)

Aldolase B Deficiency

• hereditary fructose intolerance
• normally aldolase B converts F-1-P to DHAP and glyceraldehyde
• hypoglycemia, elevated F-1-P inhibits glycogen phosphorylase, thus inhibiting glycogenolysis
• gluconeogenesis is inhibited because aldolase B is required for glucose sthesis from glyceraldehyde-3-P and DHAP

Fructosuria

• caused by a deficiency in fructokinase
• rare and benign genetic disorder
• no toxic metabolites of fructose accumulate in liver

The Polyol Pathway

• converts D-Glucose --aldose reductase-> sorbitol(polyol)--sorbitol dhase-> D-Fructose
• pathway is present in seminal vessicles, which syn fructose for seminal fluide(spermatazoa use fructose as major fuel source while in seminal fluid)
• elevated plasma glucose or galactose in the blood results in accumulation of sorbitol or galactitol in the lens(causes increased osmotoic pressure and glycation of lens proteins causing an opaque cloudyness called cataracts)
• galacititol is not further metabolized and diffuses out of the lens very slowly, thus hypergalactosemia is even more likel to cause cataract than hyperglycemia

Galactose Metabolism

• first converted to Galactose-1-P using galactokinase and ATP
• then coverted to GLucose-1-p and UDP galactose using galactose-1-P uridylytransferase and UDP-Glucose
• epimerase can convert UDP-Galactose back to UDP-Glucose
• non-classical galactosemia is at galactokinase and classical galactosemia is at Ga-1-P uridylyltransferase

Oxidative Branch of Pentose Phosphate 

Pathway

• G-6-P is first converted to 6-phosphoglucono-δ-lactone by g-6-p dehydrogenase(also goes NADP to NADPH)
• then glucolactonase converts to phosphogluconate which is converted to ribulose-5-phosphate
• G6PD is the rate limiting enzyme of pentose phosphate shunt and is inhibited by NADPH and induced by inculin
• G6PD affects 7% of world pop and 2% of US
• patiens with G6PD may undergo hemolytic anemia when exposed to certain drugs, infections or fava beans (causes extra oxidative stress causing the anemia)

Non-Oxidative Branch of Pentose

Phosphate Pathway

• net equation is 2 fructose 6-P +glyceraldehyde 3-P <--> 3 ribose 5-P
• ribose 5-p can be converted to ribulose 5-p with an isomerase and that can be converted to xylulose 5-phosphate with an epimerase

Pentose Phosphate vs Glycolytic 

Pathway (numbers)

• 3 Glucose-6-P in pentose pathway generates 6 mol NADPH, 3 mol CO2, 5 mol NADH, 5 mol pyruvate, 8 mol ATP
• 3 Glucose-6-P in glycolytic pathway generates 6 mol NADH, 6 mol pyruvate, 9 mol ATP

G6PD defeciency in Red blood cell

• under normal conditions, continuous generation of superoxides ion from nonenzymatic oxidation of hemoglobin provides a source of ROS
• the glutathione defense system can be compromised by G6PD deficiency
• heniz bodies, aggregates of cross linked hemoglobin, form on cell membrane and subject the cell to mechanical stress as it tries to go through small capillaries
• action of the ROS on the cell membrane as well as mechanical stress from the lack of deformability results in hemolysis

Pathwys that require NADPH

• detoxification: reduction of oxidized glutathione, cytochrome P450 monooxygenases
• Reductive syn: fatty acid syn, fatty acid chain elongation, cholesterol syn, neurotransmitter syn, deoxynucleotide syn, superoxide syn(highest expression of G6PD found in phagocytes)

Glycolysis overview

• first step uses hexokinase and atp to generate G6P from glucose
• rate limiting step is F6P-F1,6bisP that uses ATP and the enzyme PFK-1
• 2 total ATPs are used in the preparative phase
• GPDH oxidizes the aldehyde group of G3P to a carboxyl group and transfers the electrons to NAD to form NADH
• high energy thioester bond accepts an inorganic phosphate to form a high energy bond(subs level phosphorylation)
• ATP made in next step(2 per glucose)
• ATP made in last step 2 from high energy bond(2 per glucose)

Fates of Pyruvate

• fate of pyruvate depends on route used for NADH oxidation (NAD needed for GPDH in glycolysis)
• aerobic: malate-aspartate or glycerol3P shuttles form the ETC to oxidize the NADH(pyruvate enters TCA cycle)
• anaerobic: uses lactate dehydrogenase to convert the 2 pyruvates to 2 lactates while oxidizing the NADH

Lactate Dehydrogenase

(LDH)

• used in anaerobic glycolysis: limitied supply of O2(kidney medulla or hypoxia), few or no mitochondria(RBC), greatly increased ATP demands
• LDH is a tetramer composed of M subunits and H subunits, including M4, M3H1, M2H2, M1H3 and M4
• M4 facilitates conversion of pyruvate to lactate in Skeletal muscle, whereas H4 facilitates conversion of lactate to pyruvate in the heart

Glycerol-3-P Shuttle

• major shuttle system in most tissue
• used because NADH cannot cross the inner mitochondrial membrane
• NADH donates electron to dihydroxyacetone-P(DHAP) converting it to Glycerol-3-P
• Glycerol-3-P then donates electrons to FAD to FADH2, converting it back to DHAP
• FADH2 then donates to ETC(1.5ATP)

Malate-Aspartate Shuttle

• NADH donates electrons to oxaloacetate to form malate
• malate then moves into matrix and donates electron to NAD making NADH and oxaloacetate
• oxaloacetate then undergoes a transanimase reaction to form aspartate (also forms α-KG from glutamate)
• aspartate then moves to the inter space using a glutamate, aspartate exchanger
• glutamate is then formed from α-KG when converting aspartate back to oxaloacetate
• Each NADH at the ETC can create 2.5 ATP

Cori Cycle

• Lactate is produced from glycolysis in RBC or other peripheral tissues (2 ATP and 2 lactate per glucose)
• then transported to liver when gluconeogenesis converts the two lactate to glucose using 6ATP
• this is then shuttled back to RBC

Bisphosphoglycerate(BPG) Shunt

• 1,3 bisphosphoglycerate (intermediate in glucose metabolism) can either make 3-phosphoglycerate(intm of glycolysis) or it can be converted to 2,3 BPG using a mutase
• 2,3 BPG can be converted to 3-phosphoglycerate using a phosphatase
• 2,3BPG serves as an allosteric inh of oxygen binding to heme, thus promoting RBC to release O2 near tissues that need it(shifts curve to right)

Regulation of Glycolysis

• hexokinase is inhibited by its product G6P but its liver counterpart glucokinase is not
• PFK-1(rate limmiting enzyme) is activated by AMP and F-2,6-bisP(made from PFK-2)
• PFK-1 is inhibited by ATP and citrate
• pyruvate Kinase is activated by F-1,6bisP and inhibited by ATP
• pyruvate dhase(does pyruvate to acetylCoA) is activated by ADP, and Ca+ and inhibited by NADH and acetyl CoA

PFK-1

• rate limiting enzyme of glycolysis
• has six binding sites: two substrate sites(ATP and fructose6P), four allosteric regulatory sites(ATP, citrate, AMP, and Fructose2,6bisP)
• consists of three subunits: m(muscle), L(liver) and C(common)
• both m and l are sensitive to AMP and ATP regulation but c subunits are much less so

Pyruvate Kinase

• isoenzymes: R(red blooc cells), L(liver): can be inhibited through phosphorylation by cAMP and PKA during fasting; and M1/M2(muscle and other tissues)
• activators:fructose 1,6-bis-P
• inhibitor: ATP

Pyruvate Dehydrogenase

• can be inactivated trhough rapid phosphorylation(PDK4)
• activators: ADP, Ca2+
• inhibitor: NADH, acetyl CoA

Lactic Acidosis

• Lactase levels > 5mM; blood pH < 7.2
• results from increased NADH/NAD ratio in tissues
• an example is consumption of large amounts of alcohol
• decreased oxidation of NADH by ETC leads to pyruvate to lactate and fatty acids to triglycerides
• can be caused by arresting the TCA cycle, ETC, or the proteins involved in these pathways through mutation

Structure of glycogen

• after a meal, excess glucose is converted to glycogen in the liver and muscle
• glycogen is a branched glucose polysaccharide consisting of glycosyl unites linkers by α-1,4 bonds with α-1,6 branches every 8 to 10 residues
• the reducing end(growing end) glucose is attached to glycogenin
• the branched structure permits rapid degradation and synthesis of glycogen

Function of Glycogen in Skeletal Muscle

and Liver

• glycogen is degraded to glucose1phosphate, which is converted to G6P
• in SM, G6P enters anaerobic glycolytic pathway to generate ATP, when energy demands are high and oxygen absent
• in liver, glycogen is used for maintenance of blood glucose levels, G6P is hydrolyzed to glucose by G6P phosphatase(only in liver and kidney)
• gluconeogenesis(syn of glucose from amino acids and other gluconeogenic precursors) in the liver supplies blood glucose during starvtion(also generates G6P
• glucagon activates both glycogenolysis and gluconeogenesis

Synthesis and Degradation of Glycogen

• D1: glycogen degradation is catalyzed by glycogen phosphorylase and a debrancher enzyme
• D2: glucose 6 phosphatase in the liver generates free glucose from glucsoe 6 phosphate 
• S3: glycogen synthesis is catalyzed by glycogen synthase and the branching enzyme
• S2: UDP-Glucose is syn from G1P: is the bra nch point for glycogen syn and other pathways requiring the addition of carbohydrate units
• S1: G6P is formed from glucose by hexokinase in most cells and glucokinase in the liver. metabolic branch point for the pathways of glycolysis, the pentose phosphate pathway and glycogen syn 

Glycogen Synthesis

• glucose is phosphorylated to G6P by hexokinase(or gluk)
• G6P is then converted to G1P by phosphoglucomutase in a reversible rx
• high energy compound UTP provides energy by adding a UDP to glucose to form UDP glucose and releases PPI(reversible but rapid hydrolysis of PPi drives the rx)
• glycogen synthase transfers a glucose residue from UDP-glucose to a glycogen primer by formation of α1,4 glycosidic bond(reaction is repeated to increase glycogen chain length 
• when the chain reaches about 11 residues a 6 to 8 residue piece is cleaved by amylo-4:6-transferase(branching enzyme) and reattached to a glucosyl unit by α1,6 bond(branching of glycogen increases sites for synthesis and degradation and enhances the solubility of the molecule

Glycogen Degradation

(glycogenolysis)

• glycogen phosphorylase α1,4 bond and posphrylates glucose to G1P, until 4 glucosyl units from a branch point
• debranching enzyme transfers a three glucosyl unit from the branch to a long chain, and cleavages a α1,6 bond of the remaining glucose as free glucose
• thus one glucose and 7to9 G1P are released for every branch point 

Disorders of Glycogen Metabolism

• Cori's disease(liver α1,6 glucosidase)
• Pompe's Disease(lysosomal α1,4 glucosidase)
• McArdie's disease(muscle)
• Hers' disease(liver)
• Von Gierke's Disease(liver)

von Gierke's Disease

(Type I liver)

• most common glycogen storage disease
• G6Pase activity is low or absent due to mutations in G6Pase gene
• G6P becomes the end product of glycogen breakdown or gluconeogenesis
• excess G6P stimulates glycogen syn and storage
• patients have hypoglycemia after short fasting or exercise
• hypoglycemia can be treated with raw starch or glucose
• patients develop hypercholesterolemia, hyperglyceridemia and increased serum lipoproteins(VLDL)

Pompe's Disease

• Type II, all organs
• there is a defect in the lysosomal α1,4-glucosidase and the oligosaccharides that are a byproduct of glycogen breakdown accumulate in the lysosome
• eventually, the integrity of the lysosomal membrane is damaged and the lysosomal hydrolytic enzymes will leak out and cause severe liver disease

Cori's Disease

• Type III, liver, muscle
• defect or absence of α1,6 glucosidase(debranching enzyme)
• therefore, glycogen can undergo phosphorylases, but cannot be debranched so 40-50% of glucose is not accessible
• resulting limit dextrin causes severe hepatomegaly
• in case of increased energy demand, glycogen cannot supply energy fast enough and hypoglycemia may occur

Anderson's Disease

• type IV, liver
• absence of the branching enzyme results in cellulose-like, long-chain glycogen, which cannot be broken down easily because of the scarcity of the non-reducing ends and the formation of crosslinks
• therefore, the patient has difficulty in metabolizing glycogen and develops hypoglycemia
• the cellulose-like glycogen particles inhibit liver functions and cause liver failure and cell necrosis

McArdie's Disease

• type V, skeletal muscle
• caused by mutation in the muscle glycogen phosphorylase and leads to an excess of muscle glycogen deposition resulting from a lack of breakdown
• exercise induces muscle cramps and fatigue, which are relieved after 30 min by epinephrine mediated release of both glucose and fatty acids

Her's Disease

• Type VI, Liver
• mutation in liver glycogen phosphorylase or phosphorylase kinase, which leads to persistent hypoglycemia and hepatomegaly
• there are normal blood glucose levels maintained by gluconeogenesis with lactate, alanine, and glycerol as the starting materials
• ketosis is moderate and hyperlactatemia does not occur because of the use of lactate by the liver for glucose

Regulation of glycogen synthesis and degradation

• in liver, glycogen serves for the support of blood glucose during fasting(inc glucagon) and exercise(increased epin)
• syn and degradation of glycogen is regulated by changes of insulin/glucagon raito by blood glucose levels(diet)
• in skeleal muscle, glycogen serves as a reservoir of glucose for ATP generation and glycolysis
• muscle glycogenolysis is regulated by AMP, signals of a lack of ATP, and by Ca2+ releases during contraction
• epinephrine also activates muscle glycogenolysis

Regulation of Glycogen Metabolism

(Liver)

(overview)

• after a carb meal increased blood glucose levels stimulate insulin secretion from beta-cells
• increased insulin/glucagon ratio glycogen degradation and stimulates glycogen synthesis
• insulin stimulates glucose transport to peripheral tissues and stores as glycogen 
• blood glucose levels fail, insulin levels also fall, and glucagon levels increase
• decreased insulin to glucagon ratio stimulates glycogen degradation and inhibits glucogen syn
• liver glycogen is rapidly degraded to glucose and released into the blood 
• a substantial proportion of liver glycogen is degraded within the first few hours after fasting

Glycogen metabolism enzymes

• glycogen phosphorylase B(inactive) can be phosphorylized to glycogen phosphorylase a(active) with ATP
• glycogen synthase I(a) (active) can be phosphorylyzed to glycogen synthase D(or b)(inactive)
• phosphorylation done by PKA(which is activated by cAMP)
• however for glycogen phosphorylase, PKA phosphorylates a phosphorylase kinase(activating it), that then phosphorylates glucogen phosphorylase b
• protein phosphatases can dephosphorylate both enzymes

Insulin Pathway

in liver

• insulin activates PKB(AKT)
• this phosphorylates GSK3
• GSK3 phosphorylates glycogen synthetase kinase, inactivating it
• in its active form, glycogen sythetase kinase is an inhibitor of glycogen sythase
• inhibiting it, activates glycogen sythase, leading to the makeing of glycogen
• PKB can phosphorylate phosphodiesterase, activating it, so that it can convert cAMP to AMP, thus inactivating PKA
• insulin activates PP1 which dephosphorylates enzymes

Protein Phosphatase

• used in regulation of glycogen syn and degrad. in liver
• at same time that PKA and phosphorylase kinase are adding phosphate groups to enzymes, protein phosphatase removes the phosphate groups by hydrolysis
• Protein Phosphatase1(PP1) revomes phosphate grounds from phosphorylase kinase, glycogen phosphorylase and glycogen synthase
• during fasting PP1 is inactivated by dissociation from glycogen and binding of inhibitor protein 1
• insulin indirectly activates PP1 through insulin receptor signaling
• glucose activates PP1 to inhibit glycogen phosphorylase a

Epinephrine and Ca in Liver 

Glycogen regulation

• epinephrine acting at β receptors activate GPCR that activate AC to cAMP to PKA cascade
• acting at α receptors it activates phospholipase C via GPCR. this hydrolyzes PIP2 to IP3 and DAG
• IP3 stimulates release of Ca from ER, binds to calmodulin and activates Calm. dependent protein kinase and phosphorylase kinase
• Both Ca and DAG activate Protein Kinase C
• these three kinases phosphorylate glycogen synthase(inactivating it)
• phosphorylase kinase phosphorylates glycogen phosphorylase b(activating it to a form)

Skeletal Muscle difference from liver

glycogen metabolism

• glucagon has no effect on muscle glycogen(no varying with fasting/feeding)
• AMP is allosteric activator of the muscle glycogen phosphorylase b(makes structure similar to phosphorylated form) but not liver glycogen phosphorylase
• effect of Ca in muslce results from Ca released from SR after nerve impulse, not from epinephrine stimulated
• glucose does not inhibit glycogen phosphorylase a in muscle
• glycogen is a stronger feedback inhibitor of muscle glycogen synthase than in liver glycogen synthase

Glycosides

• molecules joined by a glycosidic linkage(N or O type)
• G1P is condensed to UDP-Glucose by UTP-G1Puridylyltransferase (Uses a UTP)
• this can be attached to other sugars, as in glycogen or the sugar oligosaccarides and polysaccharides side chains of proteoglycans, glycoproteins and glycolipids by glycosidic bond
• UDP glucose can be oxidized to UDP-glucuronate or epimerized to UDP-galactose(precursor for lactose)

Glycotransferases

• transfer sugars from nuleotide sugars to nucleophilic amino acid residues on proteins, such as hydroxyl group of serine or the amide group of asparagine
• bond formed btw the anomeric carbon of the sugar and the nucleophilic group of another compound is a glycosidic bond
• posses specificity for the sugar moiety and for the donating nucleotide (UDP, CMP, GDP)because the resulting proteins(or lipids) carry out functions that need regulation

Products of UDP-glucuronate

• bilirubin diglucuronide when adding bilirubin (glucuronate tranfered to carboxyl group)
• proteoglycons and glycoproteins
• iduronate(GAGs)
• UDP-xylose(GAGs)
• Gucuronides(glucuronate is transfered to alcohol group of steroids, drugs and xenobiotics)
• uses glycosidic bonds

Bilirubin diglucuronide

• a glycosidic bond is formed btw the anomeric hydroxyl of glucuronate and the caroxylate groups of bilirubin
• addition of the hydrophilic carbohydrate group and the negatively charged carboxyl group of the glucuronate, increases the water solubility of the bilirubin and allows it to be excreted in the urine or bile
• heme breakdown forms bilirubin

Lactose Synthesis

• UDP-glucose Epimerase converts UDP glucose to UDP-galactose(change in the position of a hydroxyl group at one of the asymmetric carbons)
• lactose synthase(galactosyltransferase and α-lactalbumin) is the enzyme involved in converting UDP-galactose to lactose
• it consists of the two mentioned subunits and α-lactalbumin is only present in female mamory glands
• D glucose is an acceptor that is converted to UDP during rx to lactose
• in lactose glucose β1,4 galactose is a glycosidic bond

N-acetylglucosamine 6-phosphate

formation

• first amino group is transfered from glutamine to Fructose 6-phosphate forming glucosamine 6 phosphate
• all amino sugars are derived from Glucosamine 6 phosphate (key intermediate
• N-acetyltransferase then fransfers an acetyl group from acetylCoA to the molecule to form N-acetylglucosamine 6-phosphate

Structure of Salivary Mucin

• a highly O-linked glycoprotein(no repeating disaccharides) with short linear sugar chains bound to a central core protein with a highly negative charge
• protect mucus from bacterial threats
• slippery due to charge repulsion and hydration
• sticky for positively charged molecules
• sialic acid provides a negative charged carboxyl group and the molecule is very big (N-acetylglucosamine also present)
• NANA is a sialic acid

Structure of dolichol phosphate

• lipid carrier for N-linked carbohydrate addition to proteins in the ER
• in humans, its isoprene unit is repeated aprox 17times
• sequential addition of sugar residues at non-reducing end of dolichol phosphate occurs in the lumen of the ER to generate the core sugar comples(14 invariant sugar residues) for addition to proteins at consensus glycosylation sequences N-X-S/T
• linked thorugh n-glycosidic bonds

Mannose 6-Phosphate 

Synthesis

• first a N-acetylglucosamine phosphate is transfered from UDP-NAcGlc to O-Mannose using phosphotransferase, releasing UMP and mannose 6 phosphate-1-NAcGlc
• N-acetylglucosaminidase then removes the NAcGlc from the molecule using water
• O-mannose 6-phosphate is all thats left
• the first enzyme is defective in I-cell disease
• this targets enzymes for the lysosome from the golgi

Glycolipids

• glycolipid sugars(R) are attached to ceramide
• sphingomyelin R=choline or ethanolamine
• cerbroside R=Glc(non-CNS) or Gal(cns)
• globoside R=several neutral sugars(Glc, Gal, GalNAc)
• Ganglioside R= complex carbohydrate, GM single NANA: GD two NANA: GT Three NANA GQ: 4 NANA

Blood Group Oligosaccharides

• Type A has N-acetylgalactosamine(GalNAC) at the nonreducing end
• type B has galactose(Gal)
• Type O has neighter
• R is eithe ra protein or the lipid ceramide
• all have same structure except for reducing end
• type O has mutation in transferase 

Regulation Steops of Gluconeogenesis

• substrate availability of alanine, lactate, and glycerol(ALT, LDH, Glycerol Kinase)
• allosteric activation by acetyl CoA(pyruvate carboxlase)
• Energy status, high NADH, ATP(pyruvate, isocitrate and αketoglutarate dehydrogenase)
• enzyme activation or inactivation by phosphorylation(F-2,6-Pase, PK)
• transcriptional induction of key regulatory enzymes(G6Pase, PEPCK)

Glucose Blood Levels

• Post-prandial: 135 mg/dl(7.5mM) (GLUT2)
• Fasting: 81 mg/dl (4.5 mM) 
• hypoglycemic 54 mg/dl (3.0 mM)
• normal: 90-140 mg/d:(5-8mM)

Physical Symptoms of Hypoglycemia

• hunger, drowsiness(70 mg/dL)
• weakness, warmth
• diaphoresis(sweating) 60 mg/dL (epineprine)
• anxiety, trembling
• nausea, dizziness
• confusion
• speaking difficulty(40mg/dL) brain starved of glucose
• unable to concentrate (neuroglycopenia)
• seizures
• coma

Hyperglycemia Symptoms

• draws water out of peripheral tissues
• polydipsia(water intake)
• polyuria(urine excretion)(200mg/dL)
• blurred vission
• headaches
• glycosuria(glucose in urine)
• nausea, vomiting(300 mg/dL)
• glycosylated HbA1c
• dehydration
• vessel damage
• coma

Gluconeogenesis Carbon sources

• lactate from red blood cells and muscles
• glycerol from triacylglycerol adipose tissue
• Alanine from muscle
• energy from gluconeogenesis is supplied by fatty acid catabolism, resulting in an increase in the mitochondrial level of acetyl CoA and NADH

Ethanol Metabolism

• metabolized by cytosolic alcohol dehydrogenase to acetaldehyde
• this is metabolized by mitochondrial acetaldehyde dehydrogenase to acetate
• this leads to a depletion of NAD+ co-factors 

Beta Oxidation and Pyruvate Carobxylase(PC)

• beta oxid. increases the levels of NADH in the mitochondria
• this increases acetyl-CoA levels (stops the TCA cycle by inhibiting pyruvate isocitrate, alphaketogl. dehase, and pyruvate dehydrogenase
• high acetyl-CoA levels stimulates PC to convert pyruvate to OAA
• the high levels of NADH also stimulates malate dehydrogenase to convert malate to OAA in the cytosol(malate-aspartate shuttle)

Alanine aminotransferase (ALT)

• major pathway used by the muscle to transfer branched chain amino acids(leucine, isolecuine, valine) to the liver for gluconeogenesis
• also uses ALT to convert alanine back into pyruvate in the liver

Phosphoenolpyruvate carboxykinase

(PEPCK)

• used in gluconeogenesis
• decarboxylates cytosolic OAA to phosphoenolpyruvate(PEP)
• PEPCK gene is transcriptionally induced by cAMP and glucocorticoids through CBP and glucocorticoid receptor
• then from PEP to F1,6bisphosphate the steps are reversal of glycolysis

Fructose 1,6 Bisphosphatase

*****

• hase kinase and phosphatase activity
• phosphatase activity inhibits PFK2 activity, inhibiting glycolysis and allowing conversion of F-1,6P to F6P (especially in liver)
• in muscle it does not inhibit PFK2 because muscle needs to do glycolysis
• needs better explaination, PKA activates though

Glucose 6 Phosphatase

• used in gluconeogenesis to convert G6P to glucose
• G6Pase is transcriptionally induced by cAMP and glucocorticoids similiar to PEPCK
• glucose is transported from hepatocyte by GLUT2
• glucokinase is inactivated in the fasting state but activated in fed state  by insulin

5 Classes of Lipids

• fatty acids and triglycerides
• glycerophospholipids and shingolipids
• eiconsanoids (involved in inflamation)
• cholesterol and its derivatives bile acids and steroid hormones
• fat-soluble vitamins

intestine absorption of cholesterol

• intestinal absorption of dietary cholesterol determines the amount of de novo synthesis of cholesterol in the liver and contributes to blood cholesterol levels
• dietary cholesterol is absorbed into enterocytes by diffusion and by NPC1L1, a cholesterol transporter
• cholesterol ester effluxes out of enterocyte via ABCA1 transporter to HDL
• ACAT2 can also turn cholesterol into a cholesterol ester
• Microsomal triglyceride transport protein MTP transport it to chylomicron
• Plant sterols are excreted via ABCG5/ABCG8 transporters
• deficiency in thes causes sitosterolemia in humans

Action of Pancreatic Lipase

• bile acids activate pancreatic lipases
• colipases increase lipase activity to digest triglycerides to monoacylglycerol and free fatty acids
• cholesterol esterases hydrolyze cholesterol to free cholesterol and fatty acids
• phospholipids are hydrolyzed to lysophospholipids and free fatty acids 

ApoB48 vs ApoB100

• ApoB100(liver) and ApoB48(intestine) are encoded by the same gene
• In intestine, a RNA editing enzyme converted a CAA to UAA (stop codon) in mRNA
• this shortened RNA transcript encodes ApoB48, which is 48% smaller 
• B48 does not have LDL receptor binding site that is located on the C-terminal region of B100
• therefore, chylomicrons cannot be taken up by LDL receptor

Chylomicron Maturation

• nascent Cms are secreted into the lymphatic system and enter the blood through the thoracic duct
• nascent CMs(containApoB-48) recieve ApoCII and ApoE from HDL in blood to form mature CM
• ApoE is recognized by membrane receptors. LDL receptor-related proteins(LRPs)
• ApoCII activates lipoprotein lipases(LPL) located on the surface of capilary endothelial cells in muscle and adipocytes, and digest TG to release free fatty acids from CM and VLDL
• short half life, cleard in 2-3 hours after meal
• after break down of TG, chylomicron remnant has ApoE that is recognized by receptor on liver(LDL receptor-related receptors)

Major Long Chain Fatty Acids

• Palmitate(C16)
• Stearate(C18)
• Oleate(C18:1Δ⁹) (has one double bond at carbon 9)
• Linoleate(C18:2Δ^9,12) (has 2 double bonds)
• delta means unsaturated

Activation of Long-Chain Fatty Acids

• ATP activates Fatty acid so that Fatty acyl CoA synthetase can convert to Fatty acyl-AMP(enzyme bound)
• pyroposphate is released to drive reaction(2Pi)
• CoA remains attached and an AMP is released, thus formiong Fatty acy CoA
• AMP then converted to 2ADP by adding one ATP(overall reaction uses ATP)
• synthetases: VLCFA in peroxisomes, LCFA in ER, and MCFA in mit matrix of liver

Transportation of FA into Mitochondria

• Carnitine palmitoyl-transferase(CPT1) is enzyme on outer mit membrane(rate limiting step of transportation)
• CPT1 converts Fatty acyl CoA to CoA and Fatty acylcarnitine
• CPTII on inner mitochondrial membrane converts Fatty acylcarnitine and CoA to fatty acyl CoA
• Carnitine acylcarnitine trasnlocase on inner mitochondrial membrane moves fatty acylcarnitine in and carnitine out 
• Medium chain fatty acid transported into mitochondria much easier and are activated by MCFA synthase inside mit. to fattyacylCoA

β-Oxidation Spiral

• first acyl CoA dehase converts Fatty acyl CoA to transΔ² fatty enoyl CoA and a FADH2 
• enoyl CoA hydratase and water converts it to β-hydroxy acyl CoA
• β hydroxy acyl CoA dehydrogenase then converts this to βketoacyl CoA and a NADH
• β keto thiolase then converts this back to fatty acl CoA using a CoASH. also releases an acetyl CoA
• after that step pathway starts again till degraded down to just an acetyl CoA

Energy Yield of β-oxidation

• each βoxidation cycle produces 5 ATP and an acetyl CoA
• each acetyl CoA produces 12 ATP in the TCA cycle
• each beta oxidation removes 2 carbons
• so if palmitate has C16 then you need seven cycles that yields 8 acetyl CoA's(the last cycle yields 2, one made and one left)

Oxidation of Unsaturated Fatty Acids

• additional enzymes are required for oxidation of unsaturated fatty acids
• in a β-oxidation cycle involving a double bond, only 3 ATPs are produced
• to calculate ATP production for oxidation of an unsaturated fatty acid, subtract 2 ATP for each double bond

β-Oxidation of Odd Chain Fatty Acids

• the last βoxidation cycle produces a propionyl CoA
• this is converted to succinyl CoA, an intermediate in TCA cycle
• propionyl Coa is converted to metylmatonyl CoA using propionyl CoA carboxylase(biotin) and ATP
• an epimerase and then mutase turns it to succinyl CoA
• oxidation of succinyl CoA produces 21 ATP, so oxidation of propionyl only produces 20(uses 1 to convert

Liver Lipogenesis

• First OAA is removed from citrate to form Acetyl CoA
• Acetyl CoA carboxylase then converts it to Malonyl CoA
• Malonyl CoA goes through fatty acid synthesis where NADPH to NADP to form palmitate
• Palmitate goes to FACoA and is incorporated with G3P to form a Triglyceride
• then assembled in VLDL and secreted into blood(also contains cholesterol esters and phospholipids, and ApoB100)

Glycerophospholipids

• synthesized from fatty acl CoA
• two fatty acyl-CoA are esterfied to glycerol-3-phosphate  backbone to form phosphatidic acid
• phospholipids
• plasmalogens: carbon1 is joined to a long-chain FA alcohol, which has a double bond, the heazd group is a ethanolamine or choline
• sphingolipids: backbone is phingosine; ceramide is sphingosine with a fatty acid joined to its amino group
• sphingomyelin: phosphocholine, whereas a glycolipids contain a carbohydrate group

Phospholipid 

• type of glycerophospholipid
• various head groups are added to carbon 3 of the glycerol-3-phosphate moiety to generate phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and cardiolipin

Transfer Aetyl-CoA from 

Mitochondria to cytosol

• acetyl-CoA must be converted to citrate to be transported out of mitochondria
• When Acetyl-CoA/CoA ratio increases, PDHC is inhib. and pyruvate carboxylase is stimulated to carboxylate pyruvate to OAA, which condenses with acetyl-CoA to form citrate
• that reduces acetylcoa numbers and stimulates PDHCthis reciprocal regulation stim citrate synthesis
• high AcetylCoA/CoA ratio also inhibits isocitrate dhase, causing accumulation of citrate
• citrate lyase convertes citrate to AcetylCoA and OAA 
• conversion of OAA to pyruvate creates an NADPH

OAA to Pyruvate

• OAA ends up in cytosol after citrate is broken down to it and Acetyl-CoA
• cytosolic malate dhase then converts it to malate, turning an NADH to NAD
• malate is then converted to pyruvate using malic enzyme
• this releases a NADPH and a CO2
• insulin activates almost every enzyme in FA syn

Acetyl-CoA to Malonyl CoA

• malonylCoA serves as the immediate donor of the 2carbon units that are added to the growing fatty acid chain on FA synthase complex
• AcetylCoA carobyxlase(ACC) is the rate limiting enzyme of FA syn(enzym for this reaction)

Acetyl-CoA Carboxylase(ACC) Regulation

• rate limiting enzyme of FA synthesis
• insulin stimulates a phosphatase, which dephosphorylates and activates ACC
• AMP-activated Kinase phosphorylates and inhibits ACC
• citrate feed forwardly activates ACC and palmitoyl CoA feed back inhibits ACC
• AMPK stimulates endergy product, ut inhibits biosynthesis pathways(activated by high AMP levels)

Fatty Acid Synthase Complex(FAS)

• large enzyme composed of two identical subunits, which has 7 catalytic activities and an acyl carrier protein(ACP)
• ACP contains a phosphopantetheine(derived from CoA)
• designed to prevent a futile cycle
• sequence of reactions is repeated until a chian is 16c long
• 2NADPH are required for synthesis
• malonylCoA is what enters the cycle

Elongation of Long-Chain FA in ER

• palmitate is end product of FA syn
• it is activated by palmitoyl CoA and elongated by adding 2carbon at a time
• malonyl CoA serves as the donor of the 2c units
• series of elongation rx resembles those of FA syn except that the fatty acyl chain is attached to CoA, rather than to the ACP
• palmitoyl CoA(C16) is converted to stearoylCoA(C18)
• very long chain FA (c22-26) are produced in brain

Release of Fatty Acids from adipose triglyceride

• during fasting, increase of glucagon causes cAMP levels to rise in adipose tissue and stimulates lipolysis
• PKA phosphorylates adn activates hormone-sensitive lipase, which hydrolyzes triglycerides to release free fatty acids
• fatty acids and glycerol are released into blood
• fatty acids bind to albumin and travel to muscle and other tissues for energy production

Degradation of Glycerophospholipids

• First fatty acid group broken down by Phospholipase A1
• second fatty acid group broken down(hydrolyzed) by Phospholipase A2 (second one alwasy unsaturated FA)(ex arachidonic acid)
• Phospholipase C (activated by Ca) removes head group by braking phosphate bond(also converts PIP2 to DAG and IP3
• Phosholipase D then cleaves off phosphate from head group

Adiponectin

• released from adipocytes binds to its receptors and initiates a signaling cascade to activate AMPK  and PPARα, which stimulates fatty acid oxidation in the liver and muscle
• Fibrates: lipid-lowering drugs(Lopid, Trilipix) activate PPARα, stimulate fatty acid oxidation and result in reducing serum TG
• thiazolidinedione: antidiabetic drugs(pioglitazone, ACTOS) activate PPARy in adipocytes to increase adiponectin release and stimulate fatty acid oxidation

Niemann-Pick C1-like 1 protein

(NPC1L1)

• transports dietary cholesterol into the intestine wall
• target for Ezetimibe(Zetia) to block uptake

Intestinal ABCA1

• on enterocytes
• allows for eflux of cholesterol and phospholipids into the interstitium
• there the come together with ApoA1 to form pre-beta HDL that accepts additional cholesterol from peripheral tissues to mature
• responsible for 15-20% of blood HDL (hepatic ABCA1 responsible for the rest

Sitosterolemia

• caused by a mutation in liver ABCG5/8(responsible for eflux of sitosterol cholesterol into GI lumen)
• causes increase absorption of dietary sterols and decreased bilary excretion of sterols leading to hypercholesterolemia, tendon and tuberous xanthomas, premature development of athlersclerosis and abnormal hematologic and liver function test results

De Novo Cholesterol Synthesis

• stage 1: 2 acetyl CoA used to synthesize mevalonate
• stage 2: conversion of mevalonate to two activated isoprenes
• Stage 3: condensation of 6 activated 5-carbon isoprenes to form 30 carbon squalene (24 carbons in main and six in side groups)
• Stage 4: conversion of squalene to the four ring steroid nucleus

Stage 1 of De Novo Cholesterol Synthesis

• 2 acetyl CoA are used to synthesize mevalonate
• uses HMG CoA synthase(reversible) and HMG CoA reductase(rate limiting, non reversible)
• Statins (drug) are competitive inhibitors of HMG CoA reductase, inhibiting bisynthesis

SREBP

• when cholesterol levels are high, SREBP binds with SCAP(on ER)
• SCAP is associated with insulin induced gene(Insig)
• SCAP has cholesterol sensory domain
• When cholesterol levels are low complex dissociates from Insig and goes to golgi with help of CopII
• SCAP activates S1P and S2P in golgi
• S1P cleaves in middle of SREBP and S2P cleaves nterminals to form mature SREBP(68kda)
• mature SREBP goes to SREBP1 and 2: 1 does FA(TG) synthesis and 2 does cholesterol synthesis
• effects SRE in nucleus
• insulin can inhibit SCAP-SREBP from binding to COPII

Regulation of HMG-CoA Reductase

• high amounts of Sterols(bile salts) can send it to ERAD(proteolysis degradation)
• AMPK can phosphorylate HMG-CoA, thus inactivating it 
• high AMP levels lead to the phosphorylation of AMPK that activates it
• LKB1 (AMPactivated protein kinase kinase) can also activate it using ATP
• AMPK can also phosphorylate(inactivate) ACC
• Steroid hormones can activate and glucocortocoids can inhibit?
• phosphatase can dephosphorylate HMG-CoA reductase and insulin can inhibit the phosphatase

Fates and Functions of Cholesterol

• cell membrane(fluidity and permeability)
• steroid hormones: glucocorticoids, mineralocorticoids, androgens, estrogens and progesterones
• Vitamin D: from diet (D2 or D3) or cholesterol precursor
• Bile acids: contain both polar and nonpolar regions
• storage: stored as cholesteryl esters, catalyzed by acelycoa cholesterol acyltransferase(ACAT) ACAT1is ubiquitous and ACAT2 in liver and intestine
• secretion in VLDL to the blood or to the bile from liver or in chylomicrons to the blood form intestine

LCAT

• converts free cholester to cholesterol esters
• transfers 1 fatty acid from Lecithin(PC) to the cis3 (hydroxyl group) position of a free cholesterol to form the ester and lysolecithin
• cholesterol ester is then transfered to core of HDL 
• different from ACAT 
• found in peripheral tissues to go to liver

Bile Acid Synthesis

(classical, neutral pathway)

• cholesterol is oxidized by C7αhydroxylase (CYP7A1 a cytochrome P450 Fe using enzyme) to form 7 hydroxycholesterol
• then a few(reduction, hydroxylation ect) steps to form a Diol
• the diol is then converted to Chenocholic acid(CDCA)
• ithe diol can also be converted to a triol by CYP8B1 through oxidation
• the triol is then converted to cholic acid
• both acids are primary bile acids
• CYP8B1 determines if it goes to cholic acid or not

Bile Acid synthesis

(Alternative, acid pathway)

• acounts for 6% of syn in humans and 25% in rodents
• CYP27A1 converts cholesterol to 27-hydroxycholsesterol
• CYP7B1 then converts it to CDCA after many reactions(chenocholic acid)

Secondary Bile Acids

• Deoxycholic Acid(DCA) comes from cholic acid
• Lithocholic acid comes from CDCA
• the primaries are converted to these from 7α dehydroxylase in the intestine
• they can also inhibit CYP8B1 and CYP7A1

Bile Acid absorption

*****

• absobred in intestine(95%) by ASBT 
• transported by IBABP
• then efluxed to blood through OSTα/β
• FXR is a bile acid activated nuclear receptor upregulates ASBT and OSTα/β genes and inhibits something else

Progressive Familial Intrahepatic Cholestasis

(PFIC)

• group of cholestatic conditions caused by defects in pilary epithelial transporters
• PFIC-1: mutation in ATP8B1, transports phospholipids
• PFIC-2: mutations in ABCB11(BSEP, a bile acid transporter
• PFIC-3: mutations in ABCB4 (MDR3), which transports phosphatidylcholine
• drug or pregnancy, primary biliary cirrhosis, gallstone disease, biliary atresia can also cause cholestasis(aquired)

Genetic Diseases of Bilirubin Metabolism

• Gilbert Syndrome: caused by reduced activity of the enzyme glucuronltransferase, which conjugates bilirubin for secretion
• Crigler-Najjar Syndrome: deficiency in UDP-glucuronosyl transferase(UGT1A1), leading to deficiency in glucuronidation of bilirubin(more severe then gilbert
• Dubin-Johnson syndrome: mutations in MDR prtoein 2(MRP2)

LXR

• Liver X receptor, a oxysterol activated nuclear receptor
• Upregulates genes for ABCG5/G8 and ABCA1
• both of these are involved in cholesterol
• sitosterol cholesterol exits through ABCG and cholesterol and phospholipids eflux to blood through ABCA1

ApoAI and ApoAII

• apoproteins found on HDL
• bind to SR-B1 receptor
• They are a LCAT activator
• LCAT converts free cholesterol to cholesterol ester

Metabolism of ApoB Containing Lipoproteins

• first a chylomicron is formed at intestine with TG, Cholesterol, phospholipids
• then TG are taken and a Chylomicron remnant forms with apoE and ApoB48, this is recognized by LDL like recepoter related protein on liver
• VLDL is secreted from liver with ApoB100, C and E(aquired from HDL)
• lipoprotein lipase hydrolyzes TG, and VLDL goes to IDL
• 50% of IDL is uptaken in liver through LDL receptor and the other 50% is converted to LDL using hepatic lypase

Reverse Cholesterol Transport

• pre beta HDL(nascent) is excreted from liver(FC and PL to apoA-1 effluxed through ABCA1) 
• this then accepts free cholesterol from peripheral tissue to form Spherical or mature HDL
• free cholesterol is converted to cholesterol esters by LCAT
• it can also transport ApoE and ApoC to nascent chylomicrons
• CETP can facilitate tranport of cholesterol ester from HDL to VLDL or chylomicron (in exchange for TG)
• cholesterol ester can be delivered to the liver through SR-B1(HDL receptor) 
• cholesterol esters are hydrolyzed to Free cholesterol

LDL Receptor Mediated Endocytosis

• clathrin contataining coated vesicles are internalized and deliver LDL to lysosomes
• low ph allows  LDL to break from receptors
• LDL receptors are either recycled or digested by lysosomal enzymes
• lysosomal acid lipase converts CE to FC for sorting to ER and glogi and redistributes to intracellular and plasma membranes
• in ER, FC is synthesized and converted to CE by ACAT2
• LDL receptors are syn in ER, and carbohydrates are added in golgi
• cholesterol inhibits LDL receptor and HMG-CoA reductase but stimulates ACAT expression
• LDL receptor can also be regulated by SREBP

ATP-Binding Cassette(ABC) Transporters

• super family of membrane transporters that bind ATP and transport various molecules across plasma and intracellular membranes
• 12 transmebrane domains
• Tangier disease caus ed by mutation in ABCA1. HDL biogenesis is deficient and apoA-1 is cleared by kidney
• pateints with tangier disease have low HDL, mild hyperTGemia, premature atherosclerosis, neuropathy, splenomegaly and hepatomegaly

Niemann-Pick Type C

• intracellular cholesterol transport
• lysosomal storage disease caused by mutations in NPC1(95%) or NPC2(5%)
• charactered by accumulation of cholesterol and glycolipids in lysosomes 

ApoA1 Milano

• naturally occuring mutated variant of ApoA1
• single mutation R173C
• Patients have low HDL and high TG, but no atherosclerosis and live a long life

Atherosclerosis

Coronary Heart Disease(CHD)

• high LDL-C is linked to high incidence of CHD and inverse relationship btw HDL-C and CHD 
• other causes are hypertension, diabetes and obesity 
• normal lipid profile: Total C <200mg/DL; LDL-C <130; HDL-C >45; TC/HDL-C <5 TG<160
• fatty streak secretes adhesion molecules attracted monocytes(similar to inflamtion)
• monocytes become macrophages and uptake of oxidized LDL to form foam cells
• this leads to platelet adhesion and aggregation to cytokines to to form thrombus 
• later SM cells can excrete metalloproteinases to thin the fibrous cap
• when cap is broken the atheroma can be released in blood

Statins

• lower LDL and TG and increase HDL-C
• compactin, lovastatin, pravastatin, atorvastatin(lipitor)
• HMG-CoA reductase inhibitors
• inhibit de novo cholesterol synthesis, decreasing intracellular FC, causing SREBP processing(maturing) to upregulate LDL receptor gene transcription, which results in reduced plasma cholesterol

Bile Acid Resins

• cholestyramine;lower LDL and increase HDL-C
• bind bile acids, interrupr recirculation of bile 
• stimulate cholesterol 7α-Hydroxylase and promote conversion of cholesterol to bile acids
• increase synthesis of LDL receptors and increase cholesterol clearance 

Niacin 

• also called Vitamin B3 or nicotinic Acid
• activates LPL; reduces hepatic production of VLDL
• reduces catabolism of HDL 
• lower LDL, raises HDL

Fibrates

• clofibrate, gemfibrozil, fenofibrate
• activate PPARα, increase LPL activity, reduce ApoC-III production, increase ApoA-1 production
• stimulates FFA β oxidation 
• raise HDL, lower TG a nd total cholesterol

Cholesterol and lipid lowering drugs

• statins
• bile acid resins (cholestyramine)
• niacin (vitamin B3; nicotinic acid)
• fibrates (clofibrate, gemfibrozil, fenofibrate)
• ezetimibe(zetia) inhibits NPC1L1, reduces intestinal cholesterol absorption and reduces LDL-C
• ACAT inhibitor, Vytorin(ezetimibe and simvastatin

Steroid Hormones 

• cholesterol is the precursor of all 5 classes of steroid hromones: glucocorticoids, mineralocorticoids, androgens, estrogens and progesterone
• glucocorticoids(cortisol) are stimulated by adrenal corticotrophic hormone(ACTH); Cortisol is stress-released and organ is kidney
• mineralocorticoids (aldosterone) are secreted in response to angiotensin II or II or low levels of blood Na, rising blood potassium levels(orgain:kidney)
• Androgens(testosterone) are secreted in response to luteinizing hormone(LH) organ: testes ovary
• Estrogens are secreted in response to folicle-stimulating hormone(FSH) Organ: ovarian follicle and the corpus luteum
• progesterone is secreted in response to LH organ: corpus luteum

Synthesis of Steroid Hormones

• starts with cleavage of cholesterol by Cholesterol desmolase(p450scc)(CYPIIA) in mitochondria to form pregnenolone
• In cytosol Pregnenolone is converted to progesteron by 3βHSD which can then be converted to cortisol(in mitochondria) or aldosterone
• pregnenolone can be converted to intermediate by CYP17 in ER.
• this can then go on to become androstenedione also using 3βHSD
• andro can then go to estrone(CYP19) or testosterone
• testosterone can go to estradiol(CYP19)

Synthesis of Active Vitamin D

• diets: Vitamin D2 or D3 
• sythesis from cholesterol precursor 7dehydrocholesterol
• its exposure to UV light breaks a carbon to convert to cholecalciferol(vitamin D3) 
• D3 in liver is hydroxylated to form 25-calcidiol
• calcidiol is hydroxylated by PTH 1-αhydroxylase(rate limiting) to form 1,25-dihydroxycholecalciferol(calcitriol)
• Vitamin D plays important role in regulating calcium and phosphorus homeostasis

PNPLA3

• a genetic variant in this is a major risk factor for Nonalcoholic fatty liver disease
• associated with increased hepatic TG content
• also adipocyte TG hydrolase(AGTGL, pnpla2) is low in other tissues but increased in sustained caloric excess in human liver, a major hepatic trygleceride hydrolase

Blood Amino Acid Pool

• comes from dietary and endogenous protein
• can be used for synthesis of new proteins
• can be used to make purines, pyrimidines, heme, neurotransmitters, hormones and other functional nitrogen products
• can be used for energy(converted to acetyl CoA)
• can be converted to glucose
• nitrogen waste converted to urea
• 300 to 600 gm of protein is broken down and produced/day and only 100gm is consumed a day

High Protein Meal

• all protein is functional protein, no major storage form
• causes increased insulin production to shuttle protein into muscles to build up lean body mass
• can also be converted over to acetyl-coa to make energy
• also can be sent into the liver to make other proteins

High Protein, Low Carbohydrate Diet

• Atkins or South Beach Diet
• elevated insulin levels with meals - promotes protein synthesis in muscle
• elevated glucagon levels following meals-promotes catabolism in liver with amino acid degradation to feed gluconeogenesis and resulting in urea generation
• increased urea excretion-requires increased amounts of ATP so increased FAtty oxidation in liver and increased excretion of water from the kidneys that contribute to weight loss
• decreased conversion of glucose to TG in liver and adiose-due to limited supply of carbs

Formation of Glutamine from BCAA

• BCAA is proken down into glutamate
• a nitrogen from one glutamate is then transfered to another glutamate to form a glutamine(glutamine synthetase)

Functions of Glutamine

• fuel source for the GI tract, kidneys, macrophages and lymphocytes
• excretion of ammonia(NH4) in the kidneys as a waste product helping to maintain bodys pH
• nitrogen donor for synthesis of purines, pyrimidines and the other compounds
• glutamate donor for synthesis of glutathione, arginine, proline, GABA and other compounds

Role of Glutamine in the Kidney

• glutamine can be broken down to glutamate and then to α-ketoglutarate(glutamate dhase)
• this can then enter the TCA cycle
• α-ketoglutarate can also be converted to glucose and enter the TCA cycle to produce energy
• amonnium(NH4+ can be secreted into the urine)

Role of Glutamine in the Gut

• glutamine can be converted to glutamate to α-ketoglutarate in gut to be used in the TCA cycle
• in the fed state it can come from both blood and lumen of the gut
• aspartate and glutamate can also be directly used from the lumen of the gut in fed state
• during fasting state glutamine can be used from the blood

Role of Glutamine in the Brain

• astroglial cells take up BCAAs from the blood stream and can convert them to glutamine
• this can then go back to the blood stream or to neurons
• in neurons glutamine can be used to make neurotransmitters

Cytokines and Hypermetabolic State

• can be released from macrophages and two most common are tumor necrosis factor (TNF), and IL-1
• cytokines go to pituitary and CNS and mediate release of hormones 
• epinephrine and glucocorticoids(prominent catabolic hormone)
• increase in glucagon and insulin(blocked because of other catabolic states)
• effect is severe breakdown of muscles and tissues
• increased protein breakdown and release of AA
• increased protein synthesis and AA uptake in liver (produces acute phase proteins to fight off illness)

Positive Acute Phase proteins

• levels increase during hyper metabolic state in liver
• C-reactive protien(CRP)
• coagulation factors(fibrinogen, prothrombin, factor VIII)
• complement factors
• ferritin, ceruloplasmin and haptoglobin
• Alpha 1-antitripisn and Alpha 1 antichymotrypsin
• Alpha 2-macroglobulin
• serum amyloid A and serum amyloid p component
• Alpha 1 acid glycoprotin(AGP)
• d-dimer protein and mannose binding protein

Negative Acute Phase Protiens

• proteins that liver normally makes when not in a hyper metabolic state
• decrease during hypermetabolic state
• albumin, transferrin, transthyretin, transcortin, retinol binding protien

Kwashiorkor

• low or no protein diet
• first ddecribed 1935
• severe form childhood malnutrition due 
• symptoms: irritability and anorexia, swelling feet, enlarged abdomen(Fatty liver and ascites), muscle wasting, loss of hair and teeth, dermatitis and skin depigmentation, growth retardation and immune deficiency

Marasmus

• due to lack of protein and calories
• symptoms are fretful and irritable, hungry, muscle wasting, loss of adipose tissue in thighs and buttocks, dry, loose skin, dehydration, immune deficiency with infections

Protein Calorie Malnutrition(PCM)

• kwashiokor and marasmus are old outdated terms that should not be used any more
• wide variation of deficiences btw energy(calories) and protein
• PCM(or PEM) is more appropriate term and includes the entire spectrum of malnutrition conditions due to lack of protein and or calories 

6 clinical characteristics of malnutrition

• decreased energy intake
• weight loss
• body fat loss
• muscle mass loss
• fluid accumulation
• reduced hand grip strenghth
• a minimum of 2 of the 6 is recommended for Dx of moderate or severe malnutrition

COAL transporter

• Na dependent AA cotransporter
• cysteine, ornithine, arginine, lysine
• seven other Na dependent AA co-transporters and also hydrogen transporters for peptides

Cystinuria and Hartnups diseases

• cystinuria is 1:70,000 kidney stone defective uptake cysteine leads to calculi that blocks urination(COAL transporter)-cysteine converted to cystine(oxidized form)
• hartnups defective tryptophan uptake leads to pellagra
• both from defeces in intestine

Υ-glutamyl transpeptidase(YGGT)

• takes cystine from blood and converts it to glutathione(GSH), an antioxidant
• very sensitive marker of kidney or liver damage 
• Glutathion disulfide(GSSG) can be reduced by glutathione reducase and NADPH to form glutathione(GSH)

Nitrogen Metabolism overview

• alanine aminotransferase(transamination) takes nitrogen from glutamate and adds it to pyruvate to form alanine
• alanine can also give up NH3 to αketoglutarate to form glutamate
• glutamate can be converted to αketoglutarate (glutamate dhase) to give up one NH3 to the pool requiring NAD or NADP
• NH3 can be converted to glutamine(glutamine synthetases), Urea via urea cycle(90% urine, 10% feces) and NH4+ to be excreted in urine
• NH3 can also be formed from purines and pyrimidines, bacteria urease D amino oxidase, and glutamine(glutaminase)

Glutaminase

• converts glutamine to NH3 and glutamate using H2O
• found at the periportal region of the liver and also some at kidneys and intestines
• opposed by glutamine synthetase which uses glutamate and ATP

Major Nitrogenous Urinary Excretory Products

• Urea: 12-20 gram urea nitrogen per day
• NH4: 0.14-1.5 gram ammonia nitrogen per day
• creatinine: males 14-26 mg/kg and females 11-20mg/kg
• uric acid 0.25-0.75 mg
• protein total <0.15 gram/day

Nitrogen Balance

• fed state hs a positive nitrogen balance(absorption of AA from gut (blood urea nitrogen is low)
• Fasting state you are breaking down proteins so you are in negative nitrogen balance and the blood urea nitrogen is increased
• alanine is fasting state and starvation or hypermetabolic state is glutamine(reason is alanine has one nitrogen and glutamine has 2)