Glycogenesis

Question 1

Glucose-1-phosphate is one of its substrates

Answer 1

UDP-glucose pyrophosphorylase

Question 2

Activated substrate for glycogen synthesis

Answer 2

UDP- glucose

Question 3

Synthesizes alpha-1,4-linkage between glucose molecules

Answer 3

Branching enzyme

Question 4

Synthesizes the oligosaccharide glucose primer for glycogen synthase.

Answer 4

Glycogenin

Question 5

What is the overall structure of glycogen?

Answer 5

Strongly branched polymer with glucose residues
Reducing and non-reducing end
Branches at the alpha-1,6-glucose

Question 6

What is the benefit for glycogen to have such as a structure?

Answer 6

It has multiple reducing ends because of the branches so it produces more glucose = energy

Question 7

How is glycogen synthesized?

Answer 7

1) UDP-glucose pyrophosphorylase: activated glucose synthesis
-glucose 1-P + UTP <—-> UDP-glucose + PPi (reversible)
PPi+H2O——>2Pi (Irreversible)
——————————————————————————
Glucose 1-phosphate + UDP—> UDP-glucose +2Pi
2)glycogen synthase: adding glucose via the non-reducing end via alpha-1,4.linkage. Adds glucose only to polysaccharide chain already containing four residues.
3)glycogenin: initiating glycogen synthesis, it functions as a dimer. Through self-glucosylation, it adds a glucose on their tyrosine residue. This is repeated until 5-9 residues to the typ to the hydroxyl group (O-linked glycan)
4) branching enzyme : increases solubility and increases the synthesis and degradation. They transfer alpha-1,4 and create alpha-1,6 linkage.

Question 8

How is glycogen regulated?

Answer 8

Insulin (produced after eating a meal, high energy signal), glucose and glucose-6-phosphate activate glycogen synthase
Epinephrine and glycan inhibit glycogen synthase
High energy signals —-> glycogenesis
Low energy signals —-|glycogensis

Question 9

How is glycogenolysis regulated?

Answer 9

High energy signals will activate it and low energy signals will inhibit it
Its regulated by insulin and glucagon

Question 10

What are the similarities and differences between liver vs muscle glycogenolysis ?

Answer 10

The liver makes glycogen-6-phosphate
The muscles use the glucose they make

Question 11

How does glycogen metabolism mantain glucose homeostasis?

Answer 11

During fasting, glucagon signals the liver to break down glycogen stores into glucose (glycogenolysis)
If the processes where happening at the same time at the same tissue it would be a futile cycle, nothing productive would happen

Question 12

How does insulin affect type 1 and type 2 diabetes?

Answer 12

Type 1 diabetes is an autoimmune disease that leads to the destruction of beta cells—-> no insulin is produced
Type 2 diabetes: there’s an insulin resistance (too much insulin)

Question 13

How does glucagon affect diabetes?

Answer 13

Body is experiencing biochemical starvation due to glucose not being able to be uptaken because there no insulin functional so glucagon is secreted which activated glycogenolysis and inhibits glycogenesis which increases blood glucose levels thus worsening the diabetes.
The medical intervention takes place inhibiting glucagon signaling

Question 14

Which of the following is a substrate for glycogen synthase?
A) UTP-glucose
B) Glucose 1-phosphate
C)Glucose
D) UDP-glucose

Answer 14

D) UDP-glucose

Question 15

What reactants are required for UDP-glucose synthesis?
A) glucose 6-phosphate and UTP
B)Glucose 1-phosphate and UDP
C) glucose 1-phosphate and UTP
D) glucose 1-phosphate and UDP

Answer 15

C) glucose 1-phosphate and UTP

Question 16

Synthesis of UDP- glucose is driven by ….
A) hydrolysis of UTP
B) hydrolysis of pyrophosphate
C) hydrolysis of glucose 1-phosphate
D) hydrolysis of glucose 6-phospate

Answer 16

B) hydrolysis of pyrophosphate

Question 17

Select the correctly match pair:
A) UDP-glucose-potent activator for glycogen synthase
B) glucose 6-phosphate- activated substrate for glycogen synthesis
C)branching enzyme- synthesis a 1,4- linkages between glucose molecules
D)glycogenin- synthesizes a- 1,4 linked glucose primer

Answer 17

D)glycogenin- synthesizes a- 1,4 linked glucose primer