Regulation of glycogen synthesis

Question 1

Glucose storage in animals and plants

Answer 1

Glycogen-animals

Starch- plants

Question 2

Where is the primarily place where glucose is stored

Answer 2

In liver ( 10% of weight) and muscle (1-2%)

Question 3

How the glycogen is stored

Answer 3

• alpha- rosettes containing 20-40 beta-particles

- Beta-partciles contains 55k glycogen with 2k non-reducing

Question 4

When glycogen is depleted

Answer 4

After 12-24 hours fasting in liver and 1h of strenuous exercise

Question 5

Why we store more fat than glycogen

Answer 5

Because glycogen carry a lot of water with it ( not compact)

Question 6

What are other cell types where glycogen can be stored

Answer 6

Astrocytes ( central nervous system)
Heart
Adipose tissue

Question 7

Where is UDP-glucose made

Answer 7

In any cells, but predominant in liver

Question 8

What should happen for glucogenesis to start

Answer 8

Charging the sugar molecule that will be attached

Question 9

How glucose is charged

Answer 9

By adding a nucleotide

Question 10

When can NDP-sugar pyrophosphorylase can work

Answer 10

Only when glucose has already a phosphate group and UTP ( uracil tri phosphate)

Question 11

Explain the reaction that happens with UDP-glucose

Answer 11

NDP-sugar pyrophosphorylase takes off two groups from the nucleotide and attaches the sugar with a phosphate group to it. resulting in two phosphate and a sugar nucleotide, connected with two phosphate

Question 12

First enzyme to grow the glycogen chain

Answer 12

Glycogenin

Question 13

How does glycogenin performs its functions

Answer 13

It has tyrosine in its sequence. It performs glucosyltransferase activity by attacking charged glucose first carbon and attaching to its own tyrosine or tot he tyrosine of the growing chain. UDP is removed and glucose is part of glycogenin.

Then glycogenin has another activity. Chain-extending activity. It connects the first carbon of the incoming glucose with the glucose that connected to glycogenin.

Question 14

What is the limitation of glycogenin

Answer 14

It can extend the length of the chain only for 6-8 residues

Question 15

What is the enzyme that can make long chains of glycogen

Answer 15

Glycogen synthase

Question 16

For glycogen synthase requires

Answer 16

Short chains that were premade by glycogenin

Question 17

What is the function of glycogen synthase

Answer 17

Creation of 1-4 bond.

In the non-reducing end ( 4 carbon) an new coming glucose is attached

Question 18

How does branching of glucose occur

Answer 18

The bond between carbon 4 and 5 is broken and the short chain is attached to first glucose with the 1-6 alpha glycosidic bonds

Question 19

Who does the branching of glycogen

Answer 19

Glycogen-branching enzyme

Question 20

Why is branching important?

Answer 20

Increases water solubility
And increases the number of non-reducing ends.
The more non-reducing ends-> more quickly glycogenolysing enzymes can attack glycogen

Question 21

4 step of glycogenesis with enzymes

Answer 21

• Formation of UDP-glucose (NDP-sugar-pyrophosphorylase)
• Initial short chain synthesis (glycogenin)
• Elongation (Glycogen synthase)
• Branching (Glycogen-branching enzyme)

Question 22

Three enzymes of glycogenolysis

Answer 22

• Glycogen phosphorylase
• Glycogen debranching enzyme
• Phosphoglucomutase

Question 23

What does glycogen phosphorylase do

Answer 23

Breaks 1-4 glycosidic bond and requires inorganic phosphote to be attached to the first carbon

Question 24

glycogen phosphorylase depends on

Answer 24

Pyridoxal phosphate cofactor

Question 25

What is the limitation of glycogen phosphorylase

Answer 25

It can remove glucose units only until 4 glucose are left in the branch

Question 26

What does debranching enzyme do

Answer 26

• Transferase activity of debranching enzyme. It detaches three carbon from the remaining branch.
• (1-6 alpha)Glucosidase activity of debranching enzyme. It detaches the glucose that it is left from the branch, by lysing 1-6 bond

Question 27

Debranching enzyme is not ___, that is the one glucose molecule that is detached comes without ____

Answer 27

Phosphorylase

Phosphate

Question 28

Why glucose-1-phosphate is not good and what is done to it

Answer 28

Because only glucose 6-phosphate can be used and phosphoglucomutase converts 1 to 6 , the function is reversible

Question 29

What happens to glucose-6-phoshate in the liver

Answer 29

It is dephosphorylated with glucose 6-phosphotase and then glucose is transported from ER lumen to cytosol via glucose transporter and then through GLUT 2 to the bloodstream

Question 30

Why muscles do not contribute to glucose blood concentration

Answer 30

Muscle does not contribute to blood glucose concentration, because they do not express glucose-6-phosphatase , thus it cannot leave the cell, it can be only used by glycolysis

Question 31

As soon as glucose is released into the bloodstream

Answer 31

Hexokinase I and II have high affinity for glucose, glycolysis is starte

Question 32

GLUT 4 is ___ dependent. There are a lot of GLUT 4 in ___

Answer 32

Insulin

Muscles

Question 33

Explain how glycogen phosphirylase is regulated

Answer 33

When glycogen phosphorylase is not phosphorylated it is less active ( in resting muscles). The removal of the phosphate is performed by protein phosphatases.

-When glucagon(liver) and epinephrine and increased Ca concentration or increased AMP ( in muscles), stimulate phosphrylase b kinase (pkb) , adding phosphate and thus stimulating

Question 34

Epinephrine and glucagon receptors are both ___

Answer 34

GPCRs. PKA activates PKB

Question 35

Explain how glycogenolysis is regulated with insulin

Answer 35

Insulin->PIP3->activated PKB
If PKB is active it adds phosphate to GSK3, inactivating it, allowing glycogen synthase to function.
If GSK 3 is not phosphorylated it is active and it adds phosphates on Serine resudues of glycogen synthase and it becomes inactive

Question 36

What can stimulate of protein phosphatases in glycogenolysis

Answer 36

Insulin

Glucose/G-6-P