Energy Storage

Question 0

What happens once glycogen stores have been depleted? (After 8-12 hours)

Answer 0

Gluconeogenesis

Question 1

What are the main energy stores in a 70kg man?

Answer 1

Triacylglycerols - 15kg
Glycogen - 0.4kg
Muscle proteins - 6kg

Question 2

Which two types of glycosidic bonds are present in glycogen?

Answer 2

Alpha 1-4 and a1-6

Question 3

Which bonds are the branch points in glycogen?

Answer 3

Alpha 1-6

Question 4

What does the highly branched structure of glycogen allow?

Answer 4

Many sites to which glucose residues can be added/removed, allowing rapid synthesis/degradation of glycogen

Question 5

Where is glycogen stored?

Answer 5

Granules in liver and skeletal muscle

Question 6

Why is there a limit to how much glycogen can be stored?

Answer 6

A highly polar molecule so attracts lots of water

No specialised storage tissue so has to be stored in tissues with other important functions

Question 7

What is glycogenesis?

Answer 7

Synthesis of glycogen

Question 8

Name the six enzymes needed for glycogenesis

Answer 8

Hexokinase / glucokinase in liver
Phosphoglucomutase
Glycogen synthase
Branching enzyme

Question 9

When is glycogen degraded?

Answer 9

In skeletal muscle - exercise

In liver - during fasting, stress response

Question 10

Glycogen degradation is not a reversal of the synthetic pathway. What does this allow for?

Answer 10

Greater metabolic flexibility

Independent control

Question 11

What does glycogen phosphorylase do?

Answer 11

Involved in glycogen degradation
Attacks alpha 1-4 bonds by phosphorolysis
This releases glucose residues as glucose 1P

Question 12

What does debranching enzyme do in glycogen degradation?

Answer 12

Breaks down alpha 1-6 bonds and releases free glucose.

Question 13

What does glucose 6-phosphatase do?

Answer 13

Converts glucose 6-P releases from glycogen degradation into glucose in the liver.

Question 14

Which two enzymes are regulated in glycogen synthesis/degradation?

Answer 14

Glycogen synthase

Glycogen phosphorylase

Question 15

How are the enzymes activated/inhibited in glycogen regulation?

Answer 15

Synthase - inhibited by phosphorylation and activated by dephosphorylation

Phosphorylase - inhibited by dephosphorylation and activated by phosphorylation

Regulated by glucagon and insulin

Question 16

How does insulin and glucagon regulate the enzymes of glucagon synthesis/degradation?

Answer 16

Insulin promotes dephosphorylation

Glucagon promotes phosphorylation

Question 17

What are consequences of glycogen storage diseases?

Answer 17

Too much/little glycogen can cause

• tissue damage if excessive
• fasting hypoglycaemia
• poor exercise tolerance

Question 20

What can be used in gluconeogenesis?

Answer 20

Lactate, pyruvate, amino acids and glycerol

Question 21

Which reactions is gluconeogenesis from pyruvate similar to?

Answer 21

Glycolysis

Question 22

Which enzymes are involved in gluconeogenesis from pyruvate?

Answer 22

Glucose 6-phosphatase
Fructose 1,6-bisphosphatase
Pyruvate carboxylase
PEPCK

Question 23

Which two enzymes are controlled in gluconeogenesis and how?

Answer 23

PEPCK and fructose 1,6-bisphosphatase

Activity is increased by glucagon and cortisol and decreased by insulin

Question 33

When does gluconeogenesis occur?

Answer 33

When all of the glycogen has been used up after 8-10hrs of fasting

Question 34

What is the overall equation of gluconeogenesis?

Answer 34

2 pyruvate + 4ATP + 2GTP + 2NADH

——-> glucose + 2NAD+ + 4ADP + 2GDP + 6Pi + 2H+

Question 35

List the enzymes which reduce storage of triacylglycerols.

Answer 35

Glucagon Cortisol Thyroxine Growth hormone

Question 36

What is lipogenesis?

Answer 36

Fatty acid synthesis

Question 37

What are fatty acids synthesised from and where does it occur?

Answer 37

Acetyl CoA | Cytoplasm

Question 38

What does fatty acid synthesis require and where do they come from?

Answer 38

NADPH - from the pentose phosphate pathway Acetyl CoA - comes from the mitochondria as citrate Citrate -> oxaloacetate + acetyl CoA ATP

Question 39

Where does FA synthesis occur?

Answer 39

Cytoplasm

Question 40

Describe the process of FA synthesis

Answer 40

Carried out by FA synthase complex C2 added as malonyl CoA (a C3 molecule) in each turn of the cycle to the growing FA chain with a subsequent loss of carbon dioxide

Question 41

How is malonyl CoA produced?

Answer 41

From acetyl CoA | Done by the enzyme acetyl CoA carboxylase.

Question 42

How is acetyl CoA carboxylase regulated?

Answer 42

Allosteric regulation - citrate activates and AMP inhibits Covalent modification - insulin activates by promoting its dephosphorylation and glucagon inhibits by phosphorylation

Question 43

Why are TAGs an efficient way of storing energy

Answer 43

Can be stored in bulk in an anhydrous form