Glycogen (Deevska)

Question 1

What is the preferred energy source for the brain and RBC’s, and essential for exercising muscles?

Answer 1

Glucose

Question 2

Glucose is obtained from what 3 things?

Answer 2

Diet, GNG, Glycogen stores

Question 3

True false: Dietary intake is sporadic, depends on the diet, and is always a reliable source of blood glucose.

Answer 3

False, not always a reliable source

Question 4

True/False: GNG can sustain synthesis of glucose.

Answer 4

true, but it is slow in response to low blood glucose levels

Question 5

What does glycogen do?

Answer 5

Mechanism for storing glucose in a rapidly mobilizable form, to maintain blood glucose levels…

Question 6

2 main stores of glycogen

Answer 6

Skeletal muscle- own use as energy

Liver- maintain blood glucose during early fasting

Question 7

True/False. Virtually any cell in the human body can store glycogen.

Answer 7

True

Question 8

Is more glycogen stored in liver or muscle tissue?

Answer 8

Muscle tissue= 400g

Liver= 100g

Question 9

What also comes along when you store glycogen?

Answer 9

Water makes up of about 5 times the amount of glycogen.

Question 10

What happens when there is absence of dietary glucose?

Answer 10

Glycogen is broken down to glucose and rapidly released from liver and kidney.
In muscle the same thing happens, but the muscles immediately use it as energy.

Question 11

Large molecules of glycogen exist as discrete __________ granules (Beta particles).

Answer 11

cytoplasmic

Question 12

4 steps of glycogen synthesis… a lot here…

Answer 12

1. Synthesis of Uridine diphosphate glucose.
   -Highly exergonic, traps glucose in the cell, and ensures UDP glucose is sunthesized
2. Synthesis of a primer to initiate glycogen synthesis.
3. Elongation of glycogen chains.
   -Glycogen synthase can only elongate primers
   -no primers present, protein glycogenin serves as primer and attaches UDP-glucose via alpha (1,4) glycosidic bonds.
4. Formation of branches
   Enzyme: Branching Enzyme

Question 13

Why are branches on glycogen important?

Answer 13

more branches= more soluble.

Higher surface area= very fast degradation to maintain blood glucose levels. (increase non-reducing ends)

Question 14

Glycogenolysis 4 steps.

Answer 14

Seperate set of enzymes… not just reversal of Glycogen synthesis.

1. Shortening of chains
2. Removal of branches
3. Conversion of glucose-1-P to glucose-6-P
4. Conversion of glucose-6-P to glucose (liver only)

Question 15

What is the rate limiting step in glycogen degradation?

Answer 15

(step 1) Glycogen to Glucose 1-P via Enzyme: Glycogen phosphorylase

Question 16

What does Glycogen phosphorylase need as a coenzyme?

Answer 16

Pyridoxal phosphate (PLP) (derived from vitamin B6)

Question 17

What is the enzyme involved with the removal of branches?

Answer 17

(step 2) Debranching enzyme, which is a single protein with 2 activities.

1. 4:4 transferase- breaks alpha1,4 bond and transfers to end of another chain.
2. 1:6 glucosidase

Question 18

What enzyme is involved with conversion of glucose-1-P to glucose-6-P.

Answer 18

(step3) Phosphoglucomutase. Forms Glucose1,6 bisP

Question 19

What enzyme is involved with dephosphorylation of Glucose-6-P to glucose?

Answer 19

(step4) Glucose 6-phosphatase. (Primarily in the liver)

Question 20

What does it mean to be reciprocally activated?

Answer 20

Glycogenesis is on then glycogenesis is off… vice versa

Question 21

What is activated in muscles during exercise?

Answer 21

Glycogenolysis

Question 22

What is activated immediately after eating in the liver?

Answer 22

Glycogenesis

Question 23

What begins at rest in the muscle?

Answer 23

Glycogenesis

Question 24

What happens during fasting in the liver?

Answer 24

Glycogenolysis

Question 25

What are the two main enzymes of glycogen?

Answer 25

Glycogen synthase

Glycogen phosphorylase

Question 26

How are Glycogen synthase and glycogen phosphorylase regulated?

Answer 26

Hormonal regulation

Allosteric regulation

Question 27

Can glycogen synthase and glycogen phosphorylase be active at the same time?

Answer 27

No, reciprocally activated

Question 28

True/False: Glycogen synthase is active when it is phosphorylated.

Answer 28

True

Question 29

Explain hormonal regulation.

Answer 29

Glucagon and epinephrine bind leads to cAMP (2nd messenger) activating PKA which activates phosphoylase kinase.

Question 30

How does glucagon, glucose, and glycogen react to each other?

Answer 30

Glucagon is secreted by low levels of glucose. Glycogen must be broken down to maintain blood glucose levels.

Question 31

When insulin is secreted insulin binds in ____ and _____ cells.

Answer 31

Liver and muscle

Question 32

Glucose6-P activates ___________ in liver and muscle.

Answer 32

Glycogen synthase

Question 33

In muscle, AMP, Ca2+ activates __________.

Answer 33

Glycogen