Energy Storage

Question 1

Write the four steps in glycogenesis

Answer 1

Glucose + ATP —> G6P + ADP (hexokinase/glucokinase) G6P G1P (phosphoglucomutase) G1P + UTP +H2O —> UDP-glucose + 2Pi Glycogen(n residues) + UDP-glucose —> glycogen(n residues + 1) + UDP (glycogen synthase and branching enzymes)

Question 2

Write the overall equation for glycogenolysis

Answer 2

Glycogen(n residues) + nPi —> 0.9n G6P + 0.1n glucose

Question 3

Write the three steps in gycogenolysis

Answer 3

Glycogen(n) + Pi —> G1P + glycogen(n+1) (glycogen phosphorylase/branching enzymes) G1P G6P (phosphoglucomutase) G6P + H2O —> glucose + Pi

Question 4

Which bonds do glycogen phosphorylase and de-branching enzymes affect?

Answer 4

Glycogen phosphorylase - glycosidic 1,4 bonds - phosphorolysis therefore produces G1P De-branching enzyme - glycosidic 1,6 bonds - produces free glucose

Question 5

What is the difference between liver and muscle glycogen?

Answer 5

Liver - glucose store for all tissues of the body. Muscle - G6P store, only for muscles

Question 6

Which two main enzymes are used in glycogen metabolism?

Answer 6

Glycogen synthase and glycogen phosphorylase

Question 7

What inhibits glycogen synthase?

Answer 7

Phosphorylation (de phosphorylation activates glycogen synthase)

Question 8

Which three enzyme defects can lead to abnormal glycogen metabolism?

Answer 8

Glycogen phosphorylase, phosphoglucomutase and glucose-6-phosphatase (liver)

Question 9

What is the main site of gluconeogenesis?

Answer 9

Liver

Question 10

What are possible substrates for gluconeogenesis?

Answer 10

Pyruvate, lactate and glycerol can be converted to glucose. Essential and non-essential amino acids whose metabolism involves pyruvate.

Question 11

What is the overall equation for gluconeogenesis?

Answer 11

2 pyruvate + 4 ATP + 2 GTP + 2 NADH –> glucose + 2 NAD+ + 4 ADP + 2 GDP + 6Pi + 2H+

Question 12

What stimulates glycogen phosphorylase?

Answer 12

De-phosphorylation (inhibited by phosphorylation)

Question 13

How are the irreversible steps of glycolysis by-passed in gluconeogenesis?

Answer 13

1 & 3 - thermodynamically spontaneous reactions (glucose 6-phosphatase and fructose 1,6-bisphosphatase) 10 - ATP and GTP-driven hydrolysis (pyrivate carboxylase and PEPCK)

Question 14

What are the major control sites for gluconeogenesis?

Answer 14

PEPCK and fructose 1,6-phosphatase

Question 15

What stimulates PEPCK and fructose 1,6-phosphatase?

Answer 15

High glucagon, low insulin therefore insulin:anti-insulin ratio is important

Question 16

How are TAGs usually stored?

Answer 16

In an anhydrous form in adipose.

Question 17

What is the function of TAGs?

Answer 17

Store of fuel molecules for prolonged aerobic exercise.

Question 18

How is storage of TAGs controlled?

Answer 18

Hormonally: promoted by insulin, depletion activated by glucagon, cortisol, adrenaline, growth hormone and thyroxine

Question 19

How are TAGs transported to adipose tissue?

Answer 19

In chylomicrons

Question 20

Describe how fatty acid synthesis differs from fatty acid degradation (beta oxidation)

Answer 20

Question 21

Which enzyme(s) are necessary for lipogenesis?

Answer 21

Fatty acid synthase complexes

Question 22

What role does acetyl co A carboxylase play in fatty acid synthesis?

Answer 22

Controls the rate of fatty acid synthesis. Can be regulated by: allosteric regulation, regulation by covalent modification of protein structure. Insulin activates by promoting dephosphorylation and glucagon/adrenaline inhibit the enzyme by promoting phosphorylation