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Introductory Biochemistry > Glycogen Synthesis and Glycogenolysis > Flashcards

Glycogen Synthesis and Glycogenolysis Flashcards

1
Q

Why is it advantageous to store excess glucose as glycogen? 3 reasons

A
  • Less reactive than glucose, only the ends might start going through glycolysis
  • Compact energy storage
  • Keeps the solute concentration low to prevent osmotic stress
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2
Q

Why is the branching advantageous?

A

Lots of ends are rapid for rapid release or polymerization

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3
Q

How is the structure of muscle and liver glycogen different?

A

Same structure

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4
Q

Why do the muscles store glycogen?

A

For its own use during contraction

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5
Q

Why does the liver store glycogen?

A

To release into or remove glucose from the bloodstream to make sure the blood concentration is correct

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6
Q

What bond links together glucose in the linear portions of glycogen? The branches?

A

1,4 glycosidic linkages in the linear part, 1,6 glycosidic linkages in the branches

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7
Q

a) What is the first step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) Same as the first step of glycolysis
b) hexokinase
c) irreversible
d) coupled

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8
Q

a) What is the second step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) Isomerization
b) phosphoglucomutase
c) reversible
d) uncoupled

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9
Q

a) What is the third step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) nucleophilic attack of UTP by G1P
b) UDP-glucose pyrophosphatase
c) irreversible
d) coupled

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10
Q

Why is UDP-glucose a high energy intermediate?

A

UDP is a good leaving group

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11
Q

a) What is the fourth step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) addition of UDP-glucose to the chain
b) glycogen synthase
c) irreversible
d) uncoupled

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12
Q

How much energy investment is required for glycogen synthesis?

A

1 ATP and 1 UTP

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13
Q

What is the rate limiting step of glycogen synthesis?

A

The fourth step with glycogen synthase

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14
Q

a) What is the first step of glycogenolysis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) phosphorolysis
b) glycogen phosphorylase
c) Irreversible
d) Uncoupled

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15
Q

What is phosphorolysis?

A

Breaking a bond using a phosphate

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16
Q

a) What is the second step of glycogenolysis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled

A

a) isomerization
b) phosphoglucomutase
c) reversible
d) uncoupled
Shares this step with glycogen synthesis

17
Q

What happens to the G6P from glycogenolysis in the muscles?

A

It enters glycolysis and skips the first energy investment step

18
Q

What happens to the G6P from glycogenolysis in the liver?

A

It has the phosphate cleaved off by glucose-6-phosphatase and enters the bloodstream

19
Q

Why are muscle cells unable to produce glucose from glycogenolysis?

A

They don’t have the phosphatase, so any glycogen broken down is for their own use

20
Q

How does glycogen breakdown provide an immediate net advantage of ATP yield?

A

When glycogen is broken down, it enters glycolysis as G6P and skips the first energy investment step. It ends up producing 3 ATP instead of 2

21
Q

Why is glucose from glycogen technically a net disadvantage?

A

An ATP and a UTP are required to build up glycogen, which makes the net ATP yield 1

22
Q

What is the rate-limiting step of glycogenolysis?

A

The first step, glycogen phosphorylase

23
Q

How are glycogen synthesis and glycogenolysis reciprocally regulated?

A

The activity of the rate limiting steps is determined based on regulatory kinases and phosphatases. Interconversion between phosphorylated and unphosphorylated states is what changes their activity

24
Q

Is glycogen synthase active when phosphorylated or unphosphorylated?

A

Unphosphorylated

25
Q

Is glycogen phosphorylase active when phosphorylated or unphosphorylated?

A

Phosphorylated

26
Q

Does insulin activate the regulatory kinases or phosphatases? Why?

A

Phosphatases. Increasing the rate of glycogen synthesis will lower the levels of blood glucose

27
Q

Does glucagon activate the regulatory kinases or phosphatases? Why?

A

Kinases. Blood glucose levels are low, so activating glycogenolysis will increase that

28
Q

Does epinephrine activate the regulatory kinases or phosphatases? Why?

A

Kinases. We want to have lots of glucose in the blood for fight or flight

29
Q

Why isn’t hexokinase regulated in glycogen synthesis?

A

It is also present in glycolysis, so we can’t regulate one pathway without regulating the other too

Introductory Biochemistry (16 decks)

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