Biochemistry Podcast - Glycogen

Question 1

what is glycogenesis?

Answer 1

The synthesis of glycogen from glucose

Question 2

What is glycogenolysis?

Answer 2

The breakdown of glycogen to form glucose

Question 3

What is glycogen?

Answer 3

The main storage form of glucose in liver and muscle cells

Question 4

Describe liver glycogen?

Answer 4

It can be broken down in between meals to maintain the blood glucose levels and provide glucose for red blood cells and the brain

Question 5

Describe muscle glycogen?

Answer 5

It is not available to be broken down for maintenance of blood glucose levels.
It can be used only in muscle cells, and can provide energy via glycolysis and the TCA during bursts of physical activity.

Question 6

How does muscle use glycogen to provide energy during physical activity?

Answer 6

It can provide energy via glycolysis and the TCA cycle during physical activity

Question 7

Describe how blood sugar levels are kept fairly constant between meals?

Answer 7

Dietary carbs provide 100% sours of blood sugar however is rapidly depleted from the blood stream after a meal
The liver then provides a source of blood sugar between the meals via GLYCOGENOLYSIS
At night when the glycogen stores are depleted GLUCONEOGENSIS takes place which is when the liver makes new glucose from non carb products

Question 8

What is the structure of glycogen

Answer 8

glycogen is a polymer.
Single glucose molecules linked together by alpha 1-4 glycosidic links
Glycogen is branched, branches introduced every so often, formed by alpha 1-6, glycosidic links

Question 9

what is at the centre of glycogen

Answer 9

Glycogenic protein - has catalytic activity, can add small numbers of glucose molecules to itself (up to 4)

Question 10

What enzyme synthesis glycogen?

Answer 10

Glycogen synthase - can only add glucose to existing glycogen, thus it is important that something acts as a primer

Question 11

What does glycogen synthesis start with?

Answer 11

The phosphorylation of glucose to glucose-6-phosphate

Question 12

Roughly describe glycogen synthesis?

Answer 12

Glucose must be phosphorylated to glucose-6-phosphate, it must then be made into glucose-1-phosphate, the glucose-1-phosphate is activated to UDP glucose (using UTP), this UDP glucose can then be added onto an existing glycogen chain using glycogen synthase (leaving behind a UDP)

Question 13

How many ATPs does glycogen synthesis require?

Answer 13

1 ATP per molecule of glucose added

Question 14

What is UDP glucose?

Answer 14

A uridine diphosphate with a glucose molecule attached to it.
It is a nucleotide

Question 15

What is the activated form of glucose?

Answer 15

UDP glucose

Question 16

What does the phosphate ester linkage in a nucleotide sugar release?

Answer 16

Free energy on hydrolysis

Question 17

Can glycogen synthase introduce branches?

Answer 17

NO

Question 18

What is the rate limiting enzyme of glycogenesis?

Answer 18

Glycogen synthase

Question 19

What enzyme is able to introduce alpha 1-6,glycosidic branches into glycogen?

Answer 19

Transglycosylase

Adds a branch approx every 10 glucose residues

Question 20

What is the product of glycogenolysis?

Answer 20

Glucose-1-phosphate

Question 21

What catalyses glycogenolysis?

Answer 21

Glycogen phosphorylase

Question 22

What then happens to the glucose-1-phosphate in glycogenolysis?

Answer 22

It is converted into glucose-6-phosphate

Question 23

What happens to glucose-6-phosphate in the liver in glycogenolysis?

Answer 23

It can be de-phosphorlyated and the resulting glucose is released into the bloodstream

Question 24

What happens to glucose-6-phosphate in the skeletal muscle in glycogenolysis?

Answer 24

IT CANNOT de-phosphorylate it but it can use it to provide energy via glycolysis and the TCA cycle - can only feed that muscle cell

Question 25

Is the only enzyme needed to breakdown glycogen glycogen phosphorylase?

Answer 25

No you need an enzyme to breakdown the branches in the glycogen chains

Question 26

What is the rate limiting step in glycogen breakdown?

Answer 26

Glycogen phosphorylase turning glycogen into glucose-1-phosphate

Question 27

What catalyses the conversion of glucose-6-phosphate into glucose?

Answer 27

Glucose-6-phosphatase

HAPPENS ONLY IN THE LIVER

Question 28

Via what transporter does glucose made from glucose-6-phosphate enter the blood?

Answer 28

GLUT2 transporter

HAPPENS ONLY IN THE LIVER

Question 29

When does regulation of the pathways glycogenolysis and glycogenesis occur?

Answer 29

Glycogen synthase

Glycogen phosphorylase

Question 30

What does insulin do?

Answer 30

Insulin - in the fed state, stimulates synthesis of glycogen, stimulates glycogen synthase and inhibits glycogen phosphorylase

Question 31

What does glucagon do?

Answer 31

-starving state, lack of glucose in blood stream
Stimulate glycogen phosphorylase, stimulate breakdown og glycogen
Inhibit glycogen synthase

Question 32

What does adrenaline and cortisol do?

Answer 32

They stimulate glycogen phosphorylase - these hormones stimulate a need for energy

Question 33

What are the group of diseases in which there are problems with increased glycogen deposits in liver or muscle or both?

Answer 33

Glycogen storage diseases - defects in different enzymes related to glycogen synthesis and breakdown