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Bio 540 - Biochem > Exam 4 - Glycogen Metabolism > Flashcards

Exam 4 - Glycogen Metabolism Flashcards

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1
Q

The liver consumes glycogen to form []

Muscles consume glycogen to use [] []

A
  • Glucose
  • Right away
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2
Q

What type of linkage creates the linear portion of glycogen?

What type of linkage creates branch points in glycogen?

A
  1. alpha-1,4 glycosidic linkage
  2. Alpha-1,6 glycosidic linkage
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3
Q

Branching normally occurs at every [] glycosyl residue within the linear molecule…

A

fourth

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4
Q

Where are the two major sites of glycogen metabolism?

A
  • Liver
  • Muscle Cells
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5
Q

Glycogenolysis is….?

A

the breakdown of glycogen into glucose or glucose 6-phosphate

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6
Q

Glycogenesis is…

A

the synthesis of glycogen from glucose

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7
Q

If you create glucose from glycogen - what is the net formation of ATP?

Again - what is the net formation of ATP from normal glycolysis

A
  1. NET of 3 ATP since you only need to invest 1 ATP
  2. Normal glycolysis NETS you 2 ATP.
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8
Q

What are the 2 enzymes used in the formation of glycogen –> Glucose?

A
  1. Glycogen phosphorylase
  2. Phoshpglucomutase
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9
Q

What does glycogen phosphorylase catalyze?

A
  • Glycogen –> Glucose 1-phosphate
  • Pi is used to cleave the alpha-1,4 glycosidic linkage through phosphorolysis yielding glucose 1-phosphate
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10
Q

What does phosphoglucomutase catalyze?

A
  • Glucose 1-phosphate —> Glucose 6-phosphat
  • interconverst glucose 1-P and glucose 6-P
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11
Q

Phosphoglucomutase functions in both glycogen [] and []…..and requires the catalytic intermediate - []

A
  1. Synthesis
  2. degradation
  3. Glucose 1,6-bisphosphate
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12
Q

What enzyme “debranches” glycogen and what is its function?

A
  • “technically” its a 2-step enzymatic process
  • 4-alpha-d-gluconotransferase
    • removes 3 gluco residues from the linear portion
  • amylo-alpha-1,6-glucosidase
    • Makes non-phosphorylated glucose
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13
Q

What is the first step of Glycogen anabolism?

A
  • Making glucose 6-phosphate from glucose
    • hexokinase
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14
Q

What enzyme interconverts G-6-P and G-1-P for glycogen anabolism?

A
  • Phosphoglucomutase
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15
Q

What enzyme uses glucose 1-phosphate and UTP to form UDP-glucose and PPi?

A

Glucose 1-phosphate uridylyltransferase

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16
Q

What is the building block for glycogen production?

A

UDP-glucose

17
Q

What does Glucose 1-phosphate uridylyltransferase add to G-1-P to form the product = UDP-glucose??

A
  • It actually adds a Uridine MONOPhospate
  • There is already a phosphate on the glucose so it only had to add one to get the UDP…
18
Q

What enzyme catalyzes the addition of a glucose from UDP-glucose to a glycogen molecule?

Can this enzyme function to create a new storage site for glycogen?

A
  • Glycogen synthase
  • NO
    • this reaction cannot produce branches and it can only make existing glycogen bigger
19
Q

What enzyme catalyzes the addition of alpha-1,6 linked groups to a linear chain?

How man glucosyl residues does this move to a new branch?

A
  • Branching enzyme
    • 1,4-alpha-glucan branching enzyme
  • It moves 7 resides to a new branch point
20
Q

What amino acid acts as the starting molecule for glycogen?

A

Tyrosine

21
Q

How does Tyr become a “primed” starting molecule for glycogen?

What other molecule is required?

A
  1. Glycogenin
  2. This is a “self-glcosylating” molecule that adds 8 resudes of UDP-glucose to Tyrosine
  3. This forms the primed glycogenin molecule for more linear and branched UDP additions - through their respective means
22
Q

What are the 2 targets for glycogen regulation?

What type of regulation do these experience?

A
  • Glycogen Phosphorylase
  • Glycogen Synthase
  • Allosteric and Covalent Modification
23
Q

Glycogen Phosphorylase Regulation

  1. Phosphorylation by phosphorylase kinase activates the [] []
  2. Phosphorylase a is the [] form of the enzyme
  3. Phosphorylase b is the [] form of the enzyme
  4. Which “enzyme” a or b is phosphorylated?
A
  1. glycogen Phosphorylase
  2. active
  3. inactive
  4. A is phosphorylated
24
Q

Glycogen Phosphorylase Regulation

  • What are the 3 effector molecules?
  • What will glucagon signal to this enzyme (generically)
  • What will insulin signal to this enzyme (generically)
A
  • AMP (+) Phosphorylase b
  • Glucose and ATP (-) on phosphorylase a
  • Glucagon signals low blood sugar - causes glycogen phosphorylase to be more active and create glucose from glycogen
  • Insulin will signal high blood sugar - it will work to repress glycogen phosphorylase activity
25
Q

Glycogen Phosphorylase Regulation

  • How does Calcium regulate glycogen phosphorylase?
A
  • Technically it doesn’t regulate it directly.
  • However, it regulates the phosphorylase kinase a and b…..and this enzyme phosphorylates the glycogen phosphorylase
  • Calcium positively effects phosphorylase kinase a AND b
26
Q

Glycogen Synthase Regulation

  1. When Phosphorylated this enzyme is []
  2. Is this the same or opposite of the regulation for Glycogen phosphorylase?
A
  1. inactive
  2. This is opposite
    1. when phosphorylated, glycogen phosphorylase is active.
27
Q

Glucose 6-P is a [] effector on Glycogen Synthase b?

A
  • Psyche
  • Glucose 6-P does not effect glycogen synthase b
  • It is a positive effector on glycogen synthase a!
28
Q

What subunits does glycogen’s phosphoprotein phosphatase need to make it an active phosphatase?

A
  • Regulatory protiein - G
  • Catalytic subunit - C
29
Q

How does the catalytic subunit of the phosphatase become inactve?

A
  1. the catalytic subunit will be completely inactived by phosphorylation of the regulatory subunit
    1. this is done by protein kinase A
  2. Once inactive, the C subunit will then bind with an inhibitor protein - making it completely inactive.
30
Q

High levels of [] interact with the glycogen synthase to keep it in the inactive form b…

How does this mechanism work?

A
  • Glycogen
  • We dont know!

Bio 540 - Biochem (14 decks)

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