L21- Glycogen

Question 1

How is glycogen stored?

Answer 1

In cytosolic granules in muscle and liver cells of vertebrates

Question 2

What is glycogenolysis?

Answer 2

Degradation of glycogen

Question 3

What does glycogen breakdown yield?

Answer 3

Glucose 1-phosphate (G1P)
Which can be converted to glucose 6-phosphate (G6p)
for metabolism via glycolysis

Question 4

What does glycogen phosphorylase (GP) do?

Answer 4

catalyzes the sequential removal of glucose residues.
Breaking down glycogen. It stops 4 residues away from the branch point and cuts it off.
Results in a “limit dextrin” (like a y shape)which is degraded by a glycogen-debranching enzyme.
Then GP can break it down again to glucose molecules.

Question 5

How is cellular glucose converted to G6P?

Answer 5

By glucokinase in the liver cells

Question 6

What is required to incorporate one G6p into glycogen?

Answer 6

Three seperate steps

Glycogen synthase is the major regulatory step

Question 7

Where is insulin produced and what does it stimulate?

Answer 7

Produced by beta cells of the pancreas
Increase rate of glucose transport into muscle, adipose tissue
stimulates glycogen synthesis in the liver

Question 8

Where is glucagon made and what does it stimulate?

Answer 8

Produced by the alpha cells of the pancreas in response to low blood glucose
Stimulates glycogen degradation

Question 9

What does adrenaline do?

Answer 9

Released by adrenal medulla when energy is requires

stimulates breakdown of glycogen to G1p

Question 10

What is gluconeogenesis?

Answer 10

Liver and kidney make glucose from monocarbohydrate precursors such as lactate and alanine

Question 11

Which steps in glycolysis require seperate enzymes for gluconeogenesis?

Answer 11

Only the 3 irreversible steps of glycolysis

Question 12

What is the overall equation for gluconeogenisis

Answer 12

2 pyruvate + 2nadh+4atp+2gtp+6H20+2H+

goes to

glucose + 2nad+ + 4adp + 2gdp + 6Pi

Question 13

Compare the energy used in gluconeogenesis to the energy generates in glycolysis?

Answer 13

Costs more to generate glucose than energy generated in glycolysis. because neither process is 100% efficient.

Question 14

What does pyruvate carboxylase do?

Answer 14

pyruvate—> phosphoenolpyruvate

1st step of gluconeogenesis

Question 15

What is pyruvate carboxylase (PK) activated by?

Answer 15

allosterically by acetyl coA

accumulation of acetylcoA from fatty acid oxidation signals abundant energy supply so starts gluconeogenesis

Question 16

What are the precursors for gluconeogenesis?

Answer 16

Any metabolite that can be converted to pyruvate or oxolacetate. Major precursors:

1. lactate
2. most amino acids (especially alanine)
3. glycerol (from triglycerol hydrolysis)

Question 17

What is the Cori cycle?

Answer 17

Interaction of glycolysis and gluconeogenesis.
Glucose makes lactate when muscle is anaerobic. liver uses lactate for gluconeogenesis. can regenrate glucose from this. Principal supply of energy for gluconeogenesis= fatty acid breakdown

Question 18

What does glutamate dehydrogenase do in plants?

Answer 18

Incorporates ammonia into glutamate.

alpha-ketoglutarate +NH4—> glutamate +H20

Question 19

How else is ammonia assimilated (not by glutamate dehydrogenase)?

Answer 19

Via glutamine synthetase.
Glutamate +NH3–> Glutamine

uses ATP

Question 20

What is the transamination reaction in amino acid biosynthesis?

Answer 20

The amino group of glutamate is transferred to alpha keto acids generating alpha amino acids.

Question 21

In amino acid catabolism what does transamination generate?

Answer 21

Glutamate or aspartate

Question 22

What does the urea cycle do?

Answer 22

Converts ammonia into urea.
Waste nitorgen removed as it’s toxic
(birds, reptiles - uric acid instead)