Shared Flashcard Set

Details

Biochem Exam 2, part 3
Glycogenesis, Glycogenolysis, Use of Other Sugars, PPP
85
Biochemistry
Graduate
09/15/2011

Additional Biochemistry Flashcards

 


 

Cards

Term
When is glycogenesis the primary source of blood glucose?
Definition
From 3-4 hours after a meal to up to 18 hours p.c., when gluconeogenesis surpasses it as the primary source
Term
How much glycogen is stored in the liver during a fed state?
Definition
60-80g
Term
Is glycogen stored anywhere besides the liver?
Definition
Yes, it is stored in muscle cells to be utilized for internal needs
Term
What composes glycogen?
Definition
poly-α-D-glucose, attached at its reducing end to a glycogenin protein
Term
What sort of linkage creates a branch in glycogen?
Definition
An α1,6-linkage every 8-10 sugars
Term
How large can a glycogen molecule be?
Definition
It can be up to 400,000 monosaccharides, with 212 branches and several thousand non-reducing termini
Term
What is the advantage to having many non-reducing termini in a glycogen molecule?
Definition
A non-reducing end is where glucose is removed for energy, so with many branches breakdown can happen more rapidly
Term
Compare and contrast glycogen and starch
Definition
Glycogen is more branched, but both are composed of many α1,4-linked glucose
Term
What enzyme converts glucose-1-phosphate to UDP-glucose?
Definition
UDP-glucose pyrophosphorylase
Term
Does it cost energy to convert glucose-1-phosphate to UDP-glucose?
Definition
Yes, the equivalent of two ATPs
Term
What protein does glycogenesis require at initial synthesis? How does this work?
Definition
Glycogenin, which autoglucosylates itself to form a primer for glycogen synthesis
Term
What enzyme elongates the glycogenin primer with many α1,4-linked glucose?
Definition
Glycogen synthase
Term
What enzyme adds branches during glycogenesis? How does it work?
Definition
Branching enzyme Amylo-α1,4->α1,6-transglucosidase hydrolyzes 4-5 sugars from the end and transfers it to a glucose about 4 places downwards. Both new termini can be extended and branched again.
Term
What enzyme breaks down glycogen by shortening a chain, and how does it work?
Definition
Glycogen phosphorylase breaks a glycosidic bond and adds a PO4, saving energy and resulting in glucose-1-phosphate
Term
Compare α-amylase to glycogen phosphorylase
Definition
α-amylase doesn't add phosphate (so it will cost an ATP to generate glucose-1-P), and α-amylase is extracellular and less tightly controlled than intracellular glycogen phosphorylase
Term
Describe how the glucose-1-phosphate released from glycogenolysis becomes able to be transported extracellularly
Definition
1. Phosphoglucomutase converts glucose-1-phosphate to glucose-6-phosphate

2. Translocase transports it into the ER

3. glucose-6-phosphatase converts it to glucose, which can be transported extracellularly

Same technique as used in hepatic gluconeogenesis
Term
What is the alternate pathway (a few %) to breakdown glycogen?
Definition
Lysosomes break down glycogen using lysosomal α(1,4)-glucosidease (acid maltase)
Term
Define Pompe Disease
Definition
Glycogen storage disease type II: a deficiency in lysosomal α(1,4)-glucosidease (acid maltase) leads to vacuolar glycogen accumulation
Term
Define Andersen's disease
Definition
Glycogen storage disease type IV: It affect glycogen branching enzyme
Term
Define McArdle syndrome
Definition
Skeletal muscle glycogen phosphorylase deficiency

-Liver enzyme normal
-No rise in blood lactate during exercise
-Myoglobinemia and myoglobinuria
-Blood sugar normal
-Relatively benign
Term
Define Von Gierke Disease
Definition

Glucose-6-phosphate Translocase Deficiency

 

-Affects liver and kidney

-Severe fasting hypoglycemia

-Hepato and reno megaly

-Growth retardation

-High urea, lactic, lipids in blood

-So severe because the translocase is also in gluconeogenesis

Term
Describe the pathway by which glucagon/epinephrine would affect glycogenolysis
Definition

1. Glucagon/epinephrine activates adenylyl cyclase

 

2. cAMP activates protein kinase A

 

3. Protin kinase A phosphorylates Glycogen

phyosphorylase kinase to its active a form

 

4. Glycogen phosphorylase kinase a activates glycogen phosphorylase

 

5. Glycogen phosphorylase breaks down glycogen

Term
List some activators of Glycogen phosphorylase
Definition

Calcium, AMP, and protein kinase A (directly)

 

Glucagon/epinephrine (indirectly)

Term
How does calcium activate glycogen phosphorylase?
Definition

During muscle activity, Ca2+ is released

 

It then binds to the calmodulin subunit of Glycogen phosphorylase kinase, activating it without phosphorylation

 

Glycogen phosphorylase kinase then activates glycogen phosphorylase

Term
How does AMP activate glycogen phosphorylase?
Definition

AMP binds to Glycogen phosphorylase kinase, activating it without phosphorylation

 

Glycogen phosphorylase kinase then activates glycogen phosphorylase

Term
How does insulin inactivate glycogen phosphorylase?
Definition
Insulin activates protein phosphatase-1, which dephosphorylates and returns glycogen phosphorylase kinase and glycogen phosphorylase to their less active b-forms
Term
How does glucagon affect glycogen synthase?
Definition
Glucagon activates cAMP-dependent protein kinase A, which phosphorylates glycogen synthase, converting it to its b-form
Term
How does insulin affect glycogen synthase?
Definition
Insulin activates protein-phosphatase 1, which dephosphorylates glycogen synthase, converting it to its a-form
Term
What is the effect of insulin-activated protein phosphatase 1 on glycogen?
Definition
Protein phosphatase 1 converts glycogen synthase to its a form and glycogen phosphorylase to its b form
Term
List some inhibitors of glycogen phosphorylase
Definition
Glucose/Glucose-6-P, ATP, and protein phosphatase 1 directly

Insulin indirectly
Term
Describe how galactose compares to glucose
Definition
Galactose is a 4-epimer of glucose
Term
Describe how mannose is related to glucose
Definition
Mannose is a 2-epimer of glucose
Term
Where is fructose found in the diet?
Definition
55g/day on average, it occurs primarily with glucose as the diassarcharide sucrose and in fruits
Term
Where is galactose found?
Definition
With glucose as the milk disaccharide lactose, and is also a component of glycoproteins and glycolipids
Term
How does fructose, galactose, and mannose get into cells?
Definition
Transport catalyzed by GLUTs, insulin-independent
Term
How does fructose, galactose, and mannose affect insulin?
Definition
These sugars do not promote secretion of insulin
Term
Describe how fructose enters glycolysis
Definition
1. Fructose is phosphorylated by fructokinase

2. Fluctose 1-phosphate is cleaved by aldolase B into dihydroxyacetone phosphate and glyceraldehyde (bypassing control via phosphofructokinase)
Term
What is one theory suggesting why fructose corn syrup might be more fattening than traditional sugar?
Definition
When fructose-1-phosphate is cleaved by aldolase B, this step bypasses traditional glycolytic control via phosphofructokinase-1
Term
Where is fructose utilization greatest?
Definition
Liver mainly and also kidneys, because those are where fructokinase and aldolase B are most abundant
Term
When fructose-1-phosphate is split by aldolase B, what happens to the glyceraldehyde?
Definition
It can be phosphorylated by triose kinase to enter glycolysis, or reduced and phosphorylated to glycerol phosphate (a lipid precursor)
Term
Describe essential fructosuria disease
Definition
Lack of fructokinase, benign condition where fructose is wasted in the urine
Term
Define Heriditary fructose intolerance
Definition
Absence of aldolase B

Fructose-1-phosphate accumulates, wasting ATP and causing severe osmotic problems and hepatic failure
Term
Define sorbitol
Definition
A polyol derived by reduction (aldolase reductase) of the aldehyde of glucose to an alcohol, a process which traps it in the cytoplasm
Term
What area of the body is especially dependent on sorbitol?
Definition
The seminal vesicles, as it is then converted into fructose for sperm nutrient
Term
What enzyme converts glucose to sorbitol?
Definition
Aldose reductase
Term
What enzyme converts sorbitol to fructose?
Definition
Sorbitol dehydrogenase
Term
When and where does excess sorbitol become a problem?
Definition
Excess sorbitol can occur under conditions of high intracellular glucose (eg diabetes)

This can cause deleterious osmotic swelling in lens, nerves, kidneys
Term
How is mannose incorporated into glycolysis?
Definition
Mannose is trapped intracellularly and phosphorylized into mannose-6-phosphate.

It is then isomerized into fructose-6-phosphate to enter mainstream metabolism
Term
What enzyme converts mannose-6-phosphate into fructose-6-phosphate?
Definition
Phosphomannose isomerase
Term
How is galactose trapped intracellularly?
Definition
It is phosphorylaed to galactose 1-phosphate by galactokinase
Term
What enzyme converts galactose-1-phosphate and UDP glucose to UDP-galactose and glucose-1-phosphate?
Definition
galactose-1-phosphate uridyltransferase
Term
What happens to the glucose-1-phosphate generated from galactose-1-phosphate and UDP-glucose?
Definition
Phosphoglucomutase converts it to glucose-6-phosphate to enter mainstream metabolism
Term
How is UDP-galactose important in a cell?
Definition
It is a precursor for synthesis of lactose, glycolipids, glycoproteins, and glycosaminoglycans
Term
What enzyme converts UDP-Galactose to UDP-glucose?
Definition
UDP-hexose-4-epimerase
Term
Describe Galactokinase deficiency
Definition
Disorder that leads to elevated galactose in blood; can cause accumulation of galacitol by aldose reductase, causing cataracts
Term
Describe Classic galactosemia
Definition
Galactose-1-phosphate uridyltransferase deficiency, leading to accumulation of galactose-1-phosphate and galacitol

Similar metabolic and osmotic problems as hereditary fructose intolerance
Term
What is another name for the pentose phosphate pathway
Definition
Hexose monophosphate shunt
Term
Define the pentose phosphate pathway and list what the net products are
Definition
An alternative pathway of glucose oxidation, where ribose phosphate and NADPH is formed but ATP is not
Term
What happens to the NADPH formed by the pentose phosphate pathway?
Definition
They become available to enzymes involved in anabolic reactions, and for reduction of reactive oxygen species and exogenous agents
Term
Where is the pentose phosphate pathway more active?
Definition
Tissues where there is a high need for NADPH for anabolic reactions or redox regulation

examples: liver, lactating mammary gland, adipose tissue, testis, ovaries, placenta, adrenal cortex, erythrocytes
Term
How does NADPH compare to NADH?
Definition
They are identical except that NADPH has a phosphate group

NADH typically donates its electrons to the electron transport chain, whereas NADPH is typically used for anabolic reactions and ROS oxidation
Term
What is the steady state ratio of NADP+:NADPH?

What is the ratio for NAD+:NADH?
Definition
NADP+:NADPH = ~1:10

NAD+:NADH = ~1000:1
Term
What are the two phases of the pentose phosphate pathway? Briefly describe them.
Definition
Oxidative: irreversible conversion of 6 hexoses to 6 pentoses and CO2

Nonoxidative: reversible translocation of carbon chains to yield glycolytic intermediates
Term
How does glucose-6-phosphate get converted to ribulose-5-phosphate?
Definition
It is oxidized with an intermediate of 6-phosphogluconate

(not certain if need to know, but self-descriptive anyway)
Enzymes used: glucose-6-phosphate dehydrogenase, 6-phosphogluconolacetone hydrolase, 6-phosphogluconate dehydrogenase
Term
What is the important enzyme that begins the pentose phosphate pathway from glucose-6-phosphate?
Definition
Glucose-6-phosphate dehydrogenase
Term
How is the oxidative phase of the pentose phosphate pathway regulated?
Definition
It is regulated by a demand for NADPH, a strong competitive inhibitor of glucose-6-phosphate dehydrogenase

Therefore, if low NADPH, glucose-6-phosphate dehydrogenase will lead to production of pentose phosphates
Term
Is glucose-6-phosphate the only sugar that can enter the pentose phosphate pathway?
Definition
No, other glycolytic intermediates (fructose-6-phosphate, glyceraldehyde-3-phosphate) can enter on the nonoxidative side, but they skip the NADPH formation step

This would happen if ribose was needed and there were substrate supply
Term
How do the nonoxidative reactions in the pentose phosphate pathway basically work?
Definition
Glycolytic intermediates are catalyzed by transketolases and transaldolases to essentially move their carbons around to either get to ribose-6-phosphate or another intermediate

The carbon numbers in both chains will add up to 10
Term
List three dangerous hydroxyl radicals
Definition
Superoxide, hydrogen peroxide, hydroxyl radical
Term
Why is NADPH needed for reactive oxygen species?
Definition
NADPH is often the ultimate source of electrons to oxidize and get rid of the reactive oxygen species
Term
What enzyme converts hydrogen peroxide to oxygen and water?
Definition
Catalase
Term
What enzyme converts superoxide (O •2- to oxygen and hydrogen peroxide?
Definition
Superoxide dismutase
Term
Define Glutathione (GSH)
Definition
A tripeptide that can reduce H2O2 in a reaction catalyzed by glutathione peroxidase
Term
What enzyme converts 2 GSH and hydrogen peroxide to water and GSSG?
Definition
Glutathione peroxidase
Term
What happens to GSSG after the 2 G-SH have transformed hydrogen peroxide?
Definition
It is reduced and restored by oxidation of NADPH catalyzed by glutathione reductase
Term
What is the purpose of NADPH oxidase?
Definition
To transfer electrons from NADPH to O2 to generate a superoxide bactericidal respiratory burst in phagosomes
Term
What enzyme is responsible for catalyzing the bactericidal respiratory burst?
Definition
NADPH oxidase
Term
Describe NADPH oxidase deficiency
Definition
This will lead to phagocytes not being able to do the respiratory burst

Chronic disease, infections, and formation of granulomas (nodular areas of inflammation to sequester bacteria)
Term
What cells are especially dependent on the pentose phosphate pathway, and why?
Definition
Erthrocytes, because they do not have fatty acid biosynthesis pathways
Term
Describe Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency)
Definition
The most common human enzyme abnormality disease

Under stress, erthrocytes cannot undergo the pentose phosphate pathway, causing increased free radicals
Term
Define Heinz bodies
Definition
Formations in erythrocytes of hemoglobin sylfhydryl groups to protect them from free radicals under G6PD deficiency
Term
What are some stressors that can lead to symptoms of G6PD deficiency?
Definition
Oxidant drugs (antibiotics, antipyretics and antimalarials), favism (fava bean ingestion), and infection (radicals formed in inflammatory macrophages)
Term
Does G6PD deficiency become worse as the red blood cell ages?
Definition
No, G6PD naturally is used less as the cell ages, since ribosomes are no longer needed for replacement
Term
Why is G6PD the most common enzyme deficiency?
Definition
Plasmodium (malaria agents) are highly succeptible to oxidative damage, giving individuals whose red blood cells lack G6PD an advantage
Term
What enzyme can produce NADPH from fatty acid biosynthesis pathways?
Definition
NADP+ dependent malate dehydrogenase

Absent in erythrocytes
Supporting users have an ad free experience!