Lecture 6 - Glycogen Structure, Regulation of Glucogen Metabolism Flashcards Preview

Fuel Metabolism - 2016 > Lecture 6 - Glycogen Structure, Regulation of Glucogen Metabolism > Flashcards

Flashcards in Lecture 6 - Glycogen Structure, Regulation of Glucogen Metabolism Deck (50)
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1

A desirable characteristic of a storage form of glucose is that glucose can be easily deposited in the well-fed state and easily mobilized during fasting. Why is the highly branched structure of glycogen responsible for this property?

Both synthesis and degradation occur at the end of branch points, also known as the non-reducing ends

2

During what "state" does the liver store glycogen?

Fed state

3

During what "state" does the liver degrade glycogen to provide glucose?

Fasted state

4

When is glycogen degraded in the muscles?

during exercise (muscle glycogen does NOT contribute to blood glucose in the fasted state)

5

The net energy cost of incorporating each free glucose molecule into glycogen is:

2 high-energy phosphate bonds

6

What is the frequency of branching in glycogen?

every 8-10 glucose units

7

The glucose monomers within a chain are held together by ______________ bonds.

a-1,4 glycosidic bonds

8

The branch points in glycogen are created by ______________ bonds.

a-1,6 glycosidic bonds

9

"Trapping the glucose" inside the cell is the initial step in converting blood glucose to glycogen. a) How is this achieved, and b) what enzymes are used?

a) Phosphate group transferred from ATP to the C6 hydroxyl group of glucose
b) Catalyzed by tissue-specific isozymes, hexokinase, and glucokinase

10

How does insulin aid in trapping the blood glucose in the plasma membrane?

GLUT-4 transporter is recruited to plasma membrane by insulin, making more intracellular glucose available

11

How does insulin impact glucose uptake in the liver?

Insulin induces the synthesis of glucokinase, ensuring continued uptake of glucose in the liver

12

What enzyme catalyzes the conversion of Glucose-6-P to Glucose-1-P?

phosphoglucomutase

13

In order for Glucose-6-P to be stored as glycogen, it must first be converted to:

glucose-1-P

14

An essential intermediate in the conversion of glucose-6-P to glucose-1-P is:

Glucose-1,6-bisphosphate

15

What are mutases?

Enzymes that move a group from one position to another within the same molecule

16

Substrates in the formation of UDP-Glucose are Glu-1-P and UTP. What enzyme catalyzes this reaction?

UDP-glucose pyrophosphorylase

17

Glycogen synthase catalyzes the transfer of glucose from UDP-glu to _________.

A non-reducing end of the glycogen fragment

18

The transfer of glucose from UDP-glu to a non-reducing end of the glycogen fragment results in the formation of:

an a-1,4-glycoside bond

19

In the absence of a glycogen primer, what acts as an acceptor of the initial glucose residue in the transfer of glucose from UDP-glu to the glycogen fragment?

the protein glycogenin

20

What are 3 consequences of branching?

1. increased solubility
2. increased number of non-reducing ends
3. increased potential for rapid mobilization and deposition of glucose

21

How does insulin promote fuel storage?

Insulin promotes the dephosphorylation of key enzymes involved in glycogen metabolism.

22

What two molecules are antagonists of the effects of insulin?

1. Glucagon
2. Epinephrine

23

Promotion of fuel storage by insulin is medicated by what two mechanisms?

1. Insulin activates protein phosphastase
2. Insulin results in decreased levels of cAMP

24

Both glucagon and epinephrine _______ levels of cAMP in the cell

increase

25

In the fed state, what happens to the insulin/glucagon ratio?

It increases - meaning levels of insulin activate protein phosphastase 1 and glycogen synthase is active.

26

In the fasted state, what happens to the insulin/glucagon ratio?

It decreases, meaning cAMP levels are increased, and glucagon/cAMP activate Protein Kinase A.

27

What effect does phosphorylation have on glycogen synthase activity?

Phosphorylation inactivates glycogen synthase

28

A low insulin/glucagon ratio promotes:

phosphorylation of glycogen synthase

29

_________ is activated by a high insulin/glucagon ratio.

protein phosphastase 1

30

What effect does glucose-6-P have on glycogen synthase?

High concentrates of G-6-P will allosterically activate the normally inactive phospho-form of glycogen synthase.