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Biochemistry Exam 2
na
59
Biochemistry
Graduate
09/22/2012

Additional Biochemistry Flashcards

 


 

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Term
What are the three major forms of dietary sugar ?
Definition

-sucrose

-lactose 

-high fructose corn syrup (more recent form) 

Term
Sucrose
Definition

-disaccharide 

 

-made of fructose and glucose 

 

-not absorbed in the gut; must be cleaved into monosaccharides before absorption 

 

-enzyme (sucrase) cleaves sucrose in brush border of intestine 

Term
Lactose 
Definition

-milk sugar 

 

-disaccharide 

 

-made of galactose and glucose 

 

-must be hydrolyzed into individual sugar components for absorption

 

-lactase breaks down lactose 

 

 

Term
Lack of lactase causes...?
Definition

- Become lactose intolerant 

 

-without lactase you are unable to break down lactose

 

- lactose will move through the intestines without absorption, collecting water along the way which causes diarrhea and cramping 

Term
High Fructose Corn Syrup
Definition

- Man made sugar product 

 

-Large scale cleavage of sucrose; collect purified fructose 

 

-fructose is much sweeter than sucrose 

Term
3 central metabolites (key carbohydrates) in body
Definition

-G6P

 

-Pyruvate 

 

-Acetyl CoA

Term
What are sugar molecules linked to? 
Definition

-nucleotide synthesis

 

-RNA/DNA biosythesis 

 

-Fatty acid and cholesterol synthesis

 

-Protein catabolism

 

-Speciality molecule synthesis (hormones, porphyrin)

Term
Big four sugars 
Definition

-Galactose 

 

-Glucose

 

-Fructose

 

-Mannose 

Term
Xylitol
Definition

-Five carbon sugar 

 

-Proven to help prevent caries 

 

-Inhibits growth of Streptoccocus mutans and decreases ability of S. mutans to stick to teeth and biofilm

Term
What two mechanisms enable xylitol to reduce caries?
Definition

- It decreases the number of s. mutans bacteria in the oral cavity 

 

-Decreases ability of bacteria to stick to teeth and biofilm 

Term
Xylitol study information
Definition

Part 1: 10 days of pulses of different sugars of glucose, glucose/sorbitol, glucose/xylitol -> measured the number of CFUs; showed xylitol reduced CFUs 

 

Part 2: Comparison of the number of caries children had whos mother consumed xylitol containing products during pregnancy and infancy versus those mothers that did not use xylitol.

-> xylitol using mothers children had a 71% lower caries occurance 

->babies develop oral biofilm from mothers

Term
Mechanisms for metabolic control
Definition

- Tissue Specificity 

 

-Enzyme concentration

 

-Compartmentalization

 

-Protein Modification

 

-Allosteric control

 

 

Term
Tissue Specificity 
Definition

Cells and tissue have a specific activity based off of genetics. Either a cell/tissue/organ has a function or it doesn't. 

 

-Big regulator of activity 

 

-Gives specificity to metabolism

 

Examples: 

-Glucose-6-phosphatase 

-Liver pyruvate kinase 

Term
Glucose-6-phosphatase
Definition

-Example of tissue specificity 

 

-Enzyme that breaks down G6P to glucose

 

-Only expressed in hepatocytes of the liver 

 

-Differentiates hepatocytes from all other cells because of the expression of this enzyme 

Term
Liver Pyruvate Kinase 
Definition

-Example of tissue specificity 

 

-Involved with glycolysis

 

-In all cells, but in the liver this enzyme is highly regulated 

Term

Enzyme concentration 

 

Definition

-How much of a particular protein or total abundance of that protein within a cell 

 

-Different from tissue specificity because enzymes are regulated up or down; change activity of cell by changing the concentration of proteins

 

-Done at transcription and translationally level

 

Examples: 

Phosphoenolpyruvate carboxykinase (PEPCK) 

 

Term
PEPCK 
Definition

-Example of enzyme concentration

 

-Enzyme that contributes to glucose biosynthesis 

 

-Regulated at the DNA level (genes highly regulated)

 

 

Term
Compartmentalization
Definition

-Many membrane enclosed compartments in cells 

 

-More than 90% of metabolites are hydrophilic or charged. This means that they will not diffuse across the lipid bilayers.

 

-Even small molecules like H2O, urea, ammonia will not diffuse 

 

-Use proteins to transport molecules which can be regulated 

 

Examples: 

-Fatty acid bio synthesis takes place in cytoplasm

-Oxidation occurs in the mitochondria. Membrane transportation can determine if you have synthesis or degredation of fats 

Term
Protein modification
Definition

-Proteins are chemically modified after synthesis

-"Covalent chemistry" 

 

Examples:

Phosphorylation

ADP-ribosylation

Term
Phosphorylation
Definition

-Example of protein modification

 

-Most common form of protein modification

 

-Occurs at 1 of 3 AA residues that have a hydroxyl side chain residue (serine, threonine, tyrosine). 

 

-Requires ATP to do 

-Protein kinases catalyse phosphorylation

-Phosphotases remove the P and change back to -OH

Term
ADP-ribosylation
Definition

-Example of Protein modification

 

-Adds ADP-ribose to proteins 

 

-Common action of bacterial toxin -> ADP ribosylation of important enzymes in humans which cause the disease (cholera/pertussis)

Term
Allosteric control
Definition

-Enzyme has allosteric site that can bind molecules quickly causing catalytic site change. 

 

-Initiates very quickly and duration of signal can be very quick

 

-If concentration of the metabolite drops then it removes itself from allosteric site.

 

-"Fine tuner" of metabolism

 

-Allows for minimization of fluctuations in the body

 

Term
Carb Metabolism in muscle 
Definition

Red muscle: High amount of mitochondria which have a lot of iron containing enzymes (gives red color)

-burns glucose through oxidative phosphrylation and electron transport chain (makes a lot of ATP per glucose)

-uses glucose preferentially  

-Example: heart 

 

White muscle: "flight or fight" muscles

-not as much mitochondria

-uses TCA cycle and glycolysis

-Can generate glucose in anaerobic conditions 

Term
Carb metabolism in the brain
Definition

-Major glucose user 

 

-Can burn other fuels if needed (ketone bodies)

 

-

Term
Carb metabolism in RBCs 
Definition

-Exclusive user of glucose 

 

-No mitochondria so can't run citric acid cycle/no oxidative phosphorylation

 

-Depends on glycolysis to burn glucose 

 

-Can't oxidize NADH fast enough so it has a high level compared to other cells -> this drives the product of glycolysis to lactate (instead of pyruvate) 

Term
Carb metabolism in the kidney
Definition

-Main glucose user 

-At rest the brain and kidney use the most glucose 

 

-Resorbs molecules that the body needs -> depends on transport mechanisms that require glucose 

 

-Kidney cortex cells can synthesis a small amount of glucose but not enough to sustain life 

Term
Carb metabolism in the Liver 
Definition

-"Unselfish organ"  -> maintains blood glucose levels 

 

-Synthesis glucose by gluconeogenesis (hydrolyzes G6P to free glucose)

 

-Stores glucose as glycogen

 

-Both muscle and hepatocytes store glycogen but only liver calls have G6Phosphatase to convert glycogen back to free glucose (muscle can't do this and only uses it for itself 

 

-Uses fatty acids for fuel NOT glucose 

Term
Carb metabolism in the intestine
Definition

Has transporters on brush border of intestine that transport in nutrients 

 

-Transports glucose into body primarily unaltered 

 

-Burns the amino acid glutamine (20x the concentration of all other AAs in the blood)

 

-Also uses ketone bodies for fuel (biproduct of fatty acid synthesis)

Term
Metabolism is not a set of separate pathways but rather a....
Definition
seamless aggregate of hundreds of reactions taking place in a 3D world 
Term
What has the greatest impact on carbohydrate metabolism?
Definition

Insulin and Glucagon 

 

Term
Normal blood glucose levels
Definition

4.5 mM

 

(100mg/100mL)

Term
What happens when there is high blood glucose? 
Definition

-Insulin is released from Beta cells in pancreas

-Glycogen storage (synthesis) will increase in liver and muscle

-Glycogen breakdown will decrease 

-Glycolysis will increase

-Lipid synthesis increases

-Gluconeogenesis will decrease 

 

Term
What happens when there is low blood glucose?
Definition

-Alpha cells of pancrease release glucagon

-Glycogen breakdown increases

-Glycogen synthesis decreases

-Glycolysis decreases

-Gluconeogenesis increases 

Term
Where is the primary site of glucose synthesis?
Definition
The liver 
Term
Where are glucagon receptors?
Definition
Located on the liver and adipose tissues
Term
Insulin and glucagon have a ______ relationship.
Definition

Antagonistic 

 

-Glucose and lipid synthesis are dictated by the relationship between these two hormones

Term
Glucagon and epinephrine act on ______
Definition
Plasma membrane bound receptors. 
Term
G-protein coupled receptors activated by...
Definition

Glucagon

Epinephrine

ACTH

Serotonin

Term
Where is cAMP synthesized? 
Definition
In the plasma membrane of all cells 
Term
What keeps Adenylyl cyclase in it's dynamic range?
Definition

Two opposing G-protein complexes 

 

(Gsa and Gia) 

Term
What inactivates G-protein
Definition

-PGE

-Adenosine 

Term
G-protein
Definition

-Has three subunits-> alpha, beta, gamma (assume beta and gamma are same unit)

 

-Galpha can be stimulatory or inhibitory ->Gsa is stimulatory and Gia is inhibitory 

Term
Where is adenylyl cyclase located?
Definition
In the plasma membrane 
Term
Adenylyl cyclase turnover steps
Definition

1. Hormone binds to receptor which causes a conformational change 

 

2. Hormone receptor complex has high affinity for G-protein complex and binds to the Ga unit (can be S or I)

 

3.Binding of hormone causes a conformational change in the Ga -> the GDP attached to the unit is replaced by GTP and the subunit detaches from gamma/beta

 

4. Ga now has a high affinity for adenylyl cyclase and binds to it 
*Can inhibit or stimulate adenylyl cyclase at this point*

 

5. Hormone dissociates from the hormone receptor. Ga has a GTPase associated with it that cleaves GTP by itself at a rate. Once GTP is cleaved to GDP Ga no longer has affinity for adenylyl cyclase .

 

6. Ga then rejoins with beta and gamma subunits and is inactivated.

 

7. If hormone is still off balance the process will repeat itself.  

Term
Pertussis 
Definition

aka Whooping Cough

 

-Produces a protein toxin that causes ADP-ribosylation of the Gia complex in lung alveoli

 

Substrate: NAD 
Product: Nicotinamide
(what causes the ADP ribosylation)  

 

-Blocks the GDP/GTP exchange meaning:

*Never get to active Gia

*Gsa will take over and cause adenylyl cyclase activity to skyrocket (since there is no opposing Gia action).

*cAMP production does not end -> causes cells to lose H2O and Na+ which accumulates in the interstitial space of lung cells

 

-Lungs fill with fluid and can't breathe 

Term
What does cAMP regulate?
Definition
H20 and Na+ transport in cells 
Term
Cholera 
Definition

-Cholera toxin is an ADP-ribosylase that attacks the intestinal epithelium

-Same activity as Pertussis but different substrate

 

Substrate: NAD+

Product: Nicotinamide 

 

-ADP-ribosylation occurs on the Gsa-GTP 

-Blocks the action of GTPase -> causes Gsa to be locked in stimulatory mode 

 

-Never able to  turn Gs off which leads to:

*Constant activation of adenylyl cyclase 

*high levels of cAMP

*leads to H2) and Na+ loss from the intestinal epithelium

*causes massive diarrhea, dehydration and death

Term
cAMP turnover
Definition

-cAMP is produced by activated adenylyl cyclase 

 

-cAMP activates protein kinase A -> phosphorylates all kinds of proteins and is integral to metabolism regulation

 

-cAMP is broken down to 5-AMP by cyclic nucleotide phosphodiesterase 

 

*5-AMP is not a signal molecule 

Term
Cyclic nucleotide phosphodiesterase 
Definition
Enzyme responsible for breaking down cAMP to 5-AMP 
Term
What inhibits cyclic nucleotide phosphodiesterase?
Definition

Caffeine

Theophylline 

 

*causes a body rush by increased levels of cAMP -> increased heart rate, blood pressure, alertness* 

Term
Muscle and adipose response to insulin
Definition

Insulin stimulates glucose uptake and consumption

 

-increased glucose transport

 

-glucose stored in muscle as glycogen

 

-glucose stored in adipose as fat 

Term
The insulin receptor is a ...
Definition

Tyroskin kinase 

 

-causes a cascade of phosphorylation 

Term
Insulin receptors
Definition

- Located on plasma membrane 

 

-Has 2 alpha and 2 beta subunits (beta subunit transverse the membrane)

 

-Is a tyrosine specific phosphorylator 

Term

Insulin cascade 

 

Definition

-When insulin binds to insulin receptor the receptor undergoes autophosphorylation at a tyrosine. 

 

-Once it is phosphrylated it is able to phosphorylate other proteins 

 

-First one it activates is IRS-1 which has a tyrosine phosphorylated by the insulin receptor producing ADP.

 

-IRS-1 then goes off to phorphorylate other proteins 

Term
IRS-1
Definition

The first insulin receptor found

 

-Is a tyrosine kinase 

 

-once phosphorylated by the insulin receptor it goes off to activate/inactivate other proteins via phosphrylation 

Term
Many growth-related hormones are...
Definition
Tyrosine kinases 
Term
PEPCK is inhibited by
Definition
Insulin
Term
GLUT-4
Definition
Transporter that is triggered to increase glucose transport in adipose and muscle by insulin
Term
Insulin is a general enhancer of...
Definition
protein synthesis 
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