Unit 2 - Abali - Lecture 7 - Glycogen Metabolism

Question 1

Why do we store glucose as glycogen?

Answer 1

When glycogen s stored as glucose, the osmotic pressure inside and outside the cell does not become super different.

Glycogen prevents the cell membrane from exploding

Question 2

Glycogen in the liver

Answer 2

Liver stores it the most

Start of glycogenesis and glycogenolysis

Question 3

The main enzyme in glycogen conversion in the muscles

Answer 3

glycogenin

Question 4

Glycogenesis (complex mechanism)

Answer 4

1. Glucokinase phosphorylates glucose to glucose 6 phosphate
2. Glucose 6 phosphate is transformed to glucose 1 phosphate using phosphoglucomutase
3. Glucose 1 phosphate binds to UTP to form UDP glucose using UDP Glucose Phosphorylase
4. UDP glucose is hooked to glycogen, forming a 1,4 link using glycogen synthase.

Question 5

Structural rules of glucose addition to glycogen

Answer 5

glycogenin is a crucial primer

3 glucose have to exist before glycogen synthase can add UDP glucose

Question 6

Glycogenolysis mechanism

Answer 6

1. Blood sugar is low
2. pancreas produces glucagon
3. Glycogen phosphorylase breaks 1,4 bonds on liver glycogen and makes glucose 1 phosphate
4. Terminal glucosyl (outermost glucose molecules) are slowly removed until only 4 glucose molecules remain at the 1,6 branch
5. 1,6 bond on glycogen is broken and additional glucoses are freed by 1,6 glycosidase
6. glycogen phosphorylase continues to work until all glucose is freed
7. Reversible, glucose 1 phosphate can be turned back to glucose 6 phosphate

Question 7

What is glycogen metabolism?

Answer 7

break down of glycogen when blood glucose is low

Question 8

Fasting and glycogen stores

Answer 8

12-18 hrs of fasting depletes all glycogen stores

Question 9

Glycogen in skeletal muscles

Answer 9

muscles have glycogen in them, which is broken down into glucose for ATP production. This is crucial for continous muscle contraction

Question 10

Does muscle glycogen have glucose 6 phosphate

Answer 10

No. This is why the muscles never directly convert glycogen to glucose. Muscles break down glycogen into G6P.

Question 11

Describe the steps of glycogenesis (simple preface)

Answer 11

1. You eat cake
2. Body detects high amounts of glucose
3. Pancreas pumps out insulin
4. Insulin increases glucose intake into the liver
5. Glycogen synthesis begins
6. Glucose is added to glycogen in the liver

Question 12

Glycogen phosphorylase is ….

Answer 12

rate limiting

requires the highest amount of energy

Question 13

Pyridoxal phosphate and glycogen phosphorylase

Answer 13

pyridoxal phosphate is a necessary coenzyme, vitamin b6, to glycogen phosphorylase

Question 14

3 allosteric regulators of glycogen metabolism

Answer 14

glucose 6 phosphate, ATP, Adenosine monophosphate (AMP)

Question 15

Glycogen metabolism (allosteric)

Answer 15

1. Increased AMP activates glycogen phosphorylase
2. Increased ATP deactivates glycogen phosphorylase
3. High GCP inhibits glycogen phosphorylase and activates glycogen synthase

Question 16

Which hormones control glycogen metabolism?

Answer 16

epinephrine, glucagon and insulin

Question 17

Epinephrine and glucagon in hormonal regulation

Answer 17

• Epinephrine and glucagon increase cyclic AMP.

Cyclic AMP activates protein kinase.

Protein kinase disables glycogen synthase and activates phosphorylase kinase

which then activates glycogen phosphorylase

Question 18

Insulin and hormonal glycogen regulation

Answer 18

Decreases cAMP

Protein kinase is disabled

protein kinase is unable to inhibit glycogen synthase

glycogen synthase increases and glycogen phosphorylase decreases

Question 19

Response to phosphorylation

Answer 19

Glycogen synthase is DEACTIVATED when phosphorylated.

Glycogen phosphorylase is ACTIVATED when phosphorylated

Question 20

Glycogen regulation in muscle

Answer 20

in myocytes (muscle cells) epinephrine binds and activates the cascade

ATP is a negative regulator and AMP is a positive one

Question 21

Is glycogen in the muscles responsible for regulating glucose?

Answer 21

No. Muscles do not have receptors for glucagon.