Glycogen Synthesis and Glycogenolysis Flashcards
Why is it advantageous to store excess glucose as glycogen? 3 reasons
- Less reactive than glucose, only the ends might start going through glycolysis
- Compact energy storage
- Keeps the solute concentration low to prevent osmotic stress
Why is the branching advantageous?
Lots of ends are rapid for rapid release or polymerization
How is the structure of muscle and liver glycogen different?
Same structure
Why do the muscles store glycogen?
For its own use during contraction
Why does the liver store glycogen?
To release into or remove glucose from the bloodstream to make sure the blood concentration is correct
What bond links together glucose in the linear portions of glycogen? The branches?
1,4 glycosidic linkages in the linear part, 1,6 glycosidic linkages in the branches
a) What is the first step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) Same as the first step of glycolysis
b) hexokinase
c) irreversible
d) coupled
a) What is the second step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) Isomerization
b) phosphoglucomutase
c) reversible
d) uncoupled
a) What is the third step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) nucleophilic attack of UTP by G1P
b) UDP-glucose pyrophosphatase
c) irreversible
d) coupled
Why is UDP-glucose a high energy intermediate?
UDP is a good leaving group
a) What is the fourth step of glycogen synthesis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) addition of UDP-glucose to the chain
b) glycogen synthase
c) irreversible
d) uncoupled
How much energy investment is required for glycogen synthesis?
1 ATP and 1 UTP
What is the rate limiting step of glycogen synthesis?
The fourth step with glycogen synthase
a) What is the first step of glycogenolysis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) phosphorolysis
b) glycogen phosphorylase
c) Irreversible
d) Uncoupled
What is phosphorolysis?
Breaking a bond using a phosphate
a) What is the second step of glycogenolysis?
b) enzyme
c) reversible or irreversible
d) coupled or uncoupled
a) isomerization
b) phosphoglucomutase
c) reversible
d) uncoupled
Shares this step with glycogen synthesis
What happens to the G6P from glycogenolysis in the muscles?
It enters glycolysis and skips the first energy investment step
What happens to the G6P from glycogenolysis in the liver?
It has the phosphate cleaved off by glucose-6-phosphatase and enters the bloodstream
Why are muscle cells unable to produce glucose from glycogenolysis?
They don’t have the phosphatase, so any glycogen broken down is for their own use
How does glycogen breakdown provide an immediate net advantage of ATP yield?
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
Why is glucose from glycogen technically a net disadvantage?
An ATP and a UTP are required to build up glycogen, which makes the net ATP yield 1
What is the rate-limiting step of glycogenolysis?
The first step, glycogen phosphorylase
How are glycogen synthesis and glycogenolysis reciprocally regulated?
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
Is glycogen synthase active when phosphorylated or unphosphorylated?
Unphosphorylated
