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BioChem Exam 4 > Lecture 25: Glycogen Metabolism > Flashcards

Lecture 25: Glycogen Metabolism Flashcards

1
Q

What is glycogen a polymer of?

A

Glucose residues

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2
Q

How are glucose residues combined to form glycogen?

A

Linked by:
* a(1->4) glycosidic bonds [primary, linear]
* a(1->6) glycosidic bonds [branch points]

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3
Q

What does glycogen maintain?

A

Blood glucose levels

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4
Q

How does glycogen maintain blood sugar level?

A
  • When blood sugar is high, the body converts glucose into glycogen to reduce BSL
  • When blood sugar is low, glycogen breaks down to release glucose to raise the BSL
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5
Q

Where is gluclose predominately stored as glycogen?

A

Liver and muscle cells

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6
Q

Glycogen Degradation (catabolism)

What is the enam that removes glucose residues from glycogen?

A

Glycogen Phosphorylase

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7
Q

Glycogen Degradation (catabolism)

What end can glycogen phosphorylase work at?

reducing or non-reducing

A

Non-reducing end

can only go linear

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8
Q

Glycogen Degradation (catabolism)

What does glycogen phosphorylase catalyze and what does it release?

A
  • Catalizes: phosphorolytic cleavage of a(1->4)
  • Releases: glucose-1-phosphate

cannot cut a(1->6)

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9
Q

Glycogen Degradation (catabolism)

What does glucose-1-phosphate have to undergo to be used for metabolism? What does it become?

A

Isomerization to become glucose-6-phosphate

this is the active form for glycolosis and pentose phosphate pathway

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10
Q

Glycogen Degeneration (catabolism)

What enzyme is used to isomerize the glucose-1-phospahte?

A

phosphoglucomutase

is reverable

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11
Q

Glycogen Degradation (catabolism)

What must happen to glucose-6-phosphate so it be released into blood?

A

it must be dephosphorylated

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12
Q

Glycogen Degradation (catabolism)

What is the phosphate added to glucose and what is that addition called?

A

Phosphate: orthophosphate
This reaction is called: phosphorolysis

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13
Q

Glycogen Degradation (catabolism)

What is phosphorolysis similar to and how?

A

Hydrolysis

The main difference is that hydrolysis adds water while phosphorolysis adds a phosphate

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14
Q

Branching Points in Glycogen

Where does glycogen phosphorylase stop on glycogen when coming to branches?

A

4 residues away from the branch point

called the limit branch

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15
Q

Branching Points in Glycogen

What enzyme is used to cleave the branching points?

A

Debranching enzyme

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16
Q

Branching Points in Glycogen

What are the two active sites of the Debranching Enzyme?

A
  • Transferase
  • a(1->6) glucosidase
17
Q

Branching Points in Glycogen

What does the trasferase site do?

in debranching enzyme

A

transfers 3 glucose residues from the 4-residue limit to the end of another branch so the other branch is only a single residue

18
Q

Branching Points in Glycogen

What does the a(1->6) glucosidase site do?

in debranching enzyme

A

catalyzes hydrolysis of that linkage to free that glucose

19
Q

Regulation of Glycogen Degradation

What is glycogen phosphorylase regulated by?

A
  1. allosteric effectors that signal the energy state of the cell (if the cell has enough energy storage, ex: ATP, glucose, regulates how much is released based on what is already there)
  2. reversible phosphorylation
20
Q

Regulation of Glycogen Degradation

Glycogen phosphorylase exists in what 2 interconvertible forms?

A
  1. Phosphorylase a (usually in Relaxed state, R, active)
  2. Phosphorylase b (usually in Tense state, T, inactive)
21
Q

Regulation of Glycogen Degradation

Phosphorylase kinase does what for glycogen phosphorylase?

A

converts phosphorylase b to a by adding a phosphate (activates the glycogen phosphorylase)

22
Q

Regulation of Glycogen Degradation

What are critical hormones that signal for glycogen breakdown?

A
  • Glucagon
  • Epinephrine
23
Q

Regulation of Glycogen Degradation

What situlation would we need these hormones to be released?

A

When we need a sudden amount of energy released for use in something like running

24
Q

Regulation of Glycogen Degradation

What is the general pathway from the hormones to glycogen phosphorylase?

A
  1. Activate the adenylase cyclase to produce cAMP
  2. cAMP activates Protein kinase A
  3. Protein Kinase A activeates phosphorylase kinase
  4. phosphorylase kinase adds phosphate to phosphylase b to create phosphorylase a (in glycogen phosphorylase)
25
Q

Glycogen Synthesis

What is the basic definition of glycogen synthesis?

A

addition of glucose onto an existing glycogen

26
Q

Glycogen Synthesis

What is the active form of glucose that is the precursor for glycogen synthesis?

A

Uridine diphosphate glucose (UDP-glucose)

bonding of UTP to glucose-1-phosphate

27
Q

Glycogen Synthesis

What initiated glycogen synthesis?

A

Glycogenin (small protein/enam)

28
Q

Glycogen Synthesis

What does gycogenin also do?

A

Acts as the primer

builds a short linear glucose polymer behind it

29
Q

Glycogen Synthesis

What enam catalizes the elongation of the glycogen chains created by glycogenin?

A

Glycogen Synthase

30
Q

Glycogen Synthesis

Which enam controls the rate of glycogen synthesis?

glycogen synthase or glycogenin

A

Glycogen synthase

31
Q

Glycogen Synthesis

What enam controls the additions of branches onto glycogen chains?

A

Branching enam

a(1->6)

32
Q

Glycogen Synthesis

Why is branching in glycogen chains useful?

A

It increases both the rates of synthesis and the degredation by increasing potential sites of action

33
Q

Regulation of Glycogen Synthesis

What enam regulates glycogen synthesis?

A

Insulin

34
Q

Regulation of Glycogen Synthesis

What does insulin do?

A

Produced in response to High blood glucose, triggers the phosphorylation and inactivation of the glycogen synthase kinase. Prevents the phosphorylation of glycogen synthase

Phosphorylation of glycogen synthase stops it from creating glycogen

35
Q

Glycogen General

What does phosphorylation do to the enzymes for breakdown vs the enam for synthesis?

A

Breakdown: activates
Synthesis: Inactivates

BioChem Exam 4 (8 decks)

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