Bio 29 Glycogen Metabolism

Question 1

What energy products result from converting glucose into pyruvate?

Answer 1

Glucose becomes two pyruvate, and in the process 2 net ATP and 2 NADH are produced.

Question 2

What energy products result from converting pyruvate into acetyl coA?

Answer 2

A total of 2 NADH are produced from 2 pyruvate becoming two Acetyl CoA.

Question 3

What energy products result from the TCA cycle?

Answer 3

For every glucose molecule, the TCA cycle will go twice for a total production of 6 NADH, 2 FADH2, and 2 ATP. This means that half those values are made per each turn of the cycle.

Question 4

What are the total energy products from glycolysis through the TCA cycle for one glucose molecule?

Answer 4

4 ATP, 10 NADH, 2FADH2

Question 5

What happens to the NADH produced in the cytosol?

Answer 5

It cannot cross the IMM, it uses two shuttles to get its electrons into the mitochondria for energy production.
Glycerol-3P shuttle: transfers e- from NADH to FADH2 in the matrix
Malate-Aspartate shuttle: transfers e- from NADH to NADH inside the matrix

In anaerobic conditions, it gets oxidized in the conversion of pyruvate to lactate for energy production.

Question 6

Why is glucose-6P the metabolic branch point?

Answer 6

Energy can go three different ways from here:

1) Energy production through glycolysis
2) Storage as glycogen
3) Storage as fatty acids/ TAGs

Question 7

What are the active pathways for energy in the short-term fasting state in the liver?

Answer 7

Glycogen–>glucose for export
Gluconeogenesis–>glucose for export
Beta-oxidation–>produces Acetyl CoA, NADH, FADH2
TCA–>uses the Acetyl CoA from fatty acids to produce products needed for ETC
A-CoA–>Ketones for export

Question 8

What energy processes are always running and where do their substrates come from to always be running?

Answer 8

TCA and ETC/OP always running

The difference is where they get their substrates during each state.
Fed: glycolysis produces pyruvate–>Acetyl CoA for the TCA cycle which provides substrate for ETC
Fasting: Beta-oxidation produces Acetyl CoA for the TCA and then products for the ETC

Question 9

What are the three main effects of liver glycogen in the body in fed and fasting states?

Answer 9

Fed: prevents hyperglycemia
Fast: prevents hypoglycemia and spares muscle that otherwise would have been used for gluconeogenesis

Question 10

What roles does glycogen play in muscle during fed and fast states?

Answer 10

Fed: prevents hyperglycemia
Fast: short periods of fasting have little effect on muscle glycogen stores, it is used for energy in early phase of exercise but later acts mostly as primer for the TCA cycle.

Question 11

What enzyme traps glucose in the liver?

Answer 11

Glucokinase

Question 12

In peripheral tissues, what enzyme traps glucose?

Answer 12

Hexokinase

Question 13

How does the body prevent hyperglycemia after a meal?

Answer 13

Liver: Glut-2, Glucokinase, Glycogen synthesis

Muscle: Glut-4, Hexokinase, Glycogenesis

Question 14

What is the first step of glycogenesis that makes activated glucose?

Answer 14

UDP-glucose pyrophosphorylase converts glucose 1-P into UDP-glucose which is the primary building block for glycogen.

Question 15

What is the rate limiting step and enzyme of glycogenesis?

Answer 15

Glycogen synthase takes the UDP-glucose molecules and adds them to the non-reducing ends of the growing glycogen chains. These are alpha-1,4 bonds.

Question 16

What does the branching enzyme do?

Answer 16

Transfers 5-8 residues from one chain to another to make a branch. It is attached with an alpha-1,6 linkage.

Question 17

How is glycogen broken down?

Answer 17

Glycogen phosphorylase cleaves the chain one glucose at a time until 4 glucosyl units remain on each chain before a branching point. Vitamin B6 is the coenzyme of this reaction. It also requires inorganic phosphate. Glucose 1-P is released. This is the rate limiting step.
Debranching enzyme moves 3 of the 4 onto the end of another chain, and it cleaves the last residue to make glucose. This is a transferase and glucosidase activity.

Question 18

What enzyme converts Glucose 1-P into Glucose 6-P?

Answer 18

Phosphoglucomutase

Question 19

What enzyme converts G6P into glucose for export into the blood and in what tissues does this occur?

Answer 19

G6Pase

Happens in the liver and renal cortex only

Question 20

What would be inhibited in relation to glycogen if one was deficient in Vit B6?

Answer 20

Breakdown of glycogen could not occur because B6 is a coenzyme for glycogen phosphorylase.

Question 21

Where do muscles get their energy during intense exercise?

Answer 21

Primary energy source is fatty acid oxidation which produces A-CoA for the TCA cycle. But OAA is needed, so the muscle glycogen is used to prime the cycle.

Question 22

How is glycogenesis and glycogen synthase influenced by insulin, glucagon, epinephrine in liver and muscle?

Answer 22

In liver and muscle, glycogenesis is activated by insulin and inhibited by epinephrine. Only the liver is affected by glucagon. Epinephrine overrides insulin if both are present.
Glycogen Synthase is in its active form when dephosphorylated, and inactive when phosphorylated.

Question 23

What signals control the breakdown of glycogen in muscle and liver cells?

Answer 23

In order to be active, glycogen phosphorylase must be phosphorylated.

Liver: Insulin inhibits the kinase that activate glycogen phosphorylase, and epinephrine/glucagon activate it.

Muscle: Insulin and epinephrine have similar effects as in the liver. Ca2+ can also activate glycogen phosphorylase kinase which activates glycogen phosphorylase and allows for glycogenolysis. In extreme anoxic conditions, AMP can activate glycogen phosphorylase all on its own.