Metabolism 9

Question 1

Where does gluconeogenesis take place?

Answer 1

Liver

Question 2

How does the body avoid hypoglycaemia in the short term?

Answer 2

• Glycogenolysis (10-12 hours store)
• Lipolysis and beta-oxidation (mitochondrial matrix)
• Gluconeogenesis

Question 3

What is gluconeogenesis?

Answer 3

Formation of glucose form non-carbohydrate forms such as lactate, amino acids and glycerol.

Question 4

What is the effect of adrenaline on gluconeogenesis?

Answer 4

Increases the rate of gluconeogenesis and release of fatty acids from adipocytes. Also increases rate of glycolysis.

Question 5

What is the difference between glycogenic and ketogenic substances?

Answer 5

Glycogenic amino acids can enter gluconeogenesis and give rise to glucose however ketogenic amino acids can’t. Instead they are used for fatty acid and ketogenesis.

Question 6

What are examples of ketogenic substances?

Answer 6

• Acetyl-CoA

- Acetoacetyl-CoA

Question 7

What are examples of glycogenic substances?

Answer 7

• Pyruvate
• Fumarate
• Succinyl-CoA
• Oxaloacetate
• Ketoglutarate

Question 8

How are metabolic pathways controlled?

Answer 8

By introducing irreversible steps early on in the pathway.

Question 9

How does hexokinase control blood glucose level?

Answer 9

There are two isoforms of hexokinase, present in the liver and muscle tissue. They both catalyse the same reactions (first step of glycolysis - virtually irreversible) but are maximally active at different glucose concentrations.

Question 10

Which isoform is active in the liver?

Answer 10

Hexokinase II

Question 11

Which isoform is active in the skeletal muscle tissue?

Answer 11

Hexokinase I

Question 12

When is hexokinase I maximally active?

Answer 12

0.1mM - highly sensitive to inhibition.

Question 13

When is hexokinase II maximally active?

Answer 13

4.0mM as it is much less sensitive to inhibition than hexokinase I.

Question 14

How is skeletal muscle contraction maintained?

Answer 14

• Light contraction ATP consumption can be met by oxidative phosphorylation but vigorous contraction consumes ATP faster than it is made so it requires the breakdown of glycogen stores or the conversion of pyruvate to lactate.
• High concentration of glucose transporters in muscle tissue

Question 15

What energy sources can be used by the brain?

Answer 15

Ketone bodies and glucose. Fatty acids cannot be used.

Question 16

What does hyperglycaemia do to the brain?

Answer 16

Can cause permanent tissue damage.

Question 17

What does hypoglycaemia do to the brain?

Answer 17

Cause faintness and coma.

Question 18

What energy sources can cardiac muscle use?

Answer 18

Fatty acids, ketone bodies and glucose.