lecture 26 - integration of metabolism

Question 1

How is fuel used in sprinting?

Answer 1

Fuel use in a sprint:

(i) ATP stores
(ii) creatine phosphate
(iii) anaerobic glycolysis

Question 2

What is the Cori cycle?

Answer 2

Glucose converted to lactate in anaeraobic muscle is carried in the blood to the liver, where it is converted back to glucose and released back into the bloodstream. The muscle gains 2 ATP/glucose, while the liver uses 6 ATP/glucose in gluconeogenesis

Highlights the different isoforms of lactate dehydrogenase (LDH) in the body:
skeletal muscle: M4 – pyruvate -» lactate
heart: H4 – lactate -» pyruvate

H: low Km for it and inhibited by pyruvate
M: higher Km for pyruvate

Question 3

How is fuel used in a marathon?

Answer 3

Fuel use in a marathon:

(i) muscle glycogen
(ii) glucose from liver
(iii) fatty acids from fat

Question 4

Describe how Metabolic demand determines lipid fate

Answer 4

HIGH

breakdown of fatty acids to acetyl-CoA and then ketone bodies
(NOTE: FAs cannot yield glucose – TCA cycle is not biosynthetic)

LOW

FA synthesis
triacylglycerol synthesis
formation and secretion of lipoproteins

Question 5

How does starvation take place?

Answer 5

TIME

0 last meal

6 h-1 day -liver glycogen is exhausted and runs on FA breakdown
-glucose comes from:
glycerol from TAG breakdown
amino acid catabolism from muscle protein @ 75g/day
-muscle uses FA for fuel and exports pyruvate/lactate/alanine

3 days -ketone bodies produced by the liver make up 30% of brain fuel
(this reduces muscle loss, now @ 20g/day)
-heart also runs on ketone bodies

40 days -brain fuel is now ~75% ketone bodies

- fat reserves determine survival time
- after fat is exhausted, protein degradation accelerates
- death by liver/kidney/heart failure

Question 6

Describe how Gluconeogenesis is up-regulated in starvation to feed the brain with glucose

Answer 6

lactate and some amino acids converted to pyruvate
pyruvate/some amino acids converted to oxaloacetate
oxaloacetate converted to phosphoenolpyruvate
which along with glycerol is converted to DHAP and GA3P
which is then converted to glucose

Question 7

What happens when glucose levels are too low?

Answer 7

ketone bodies take over
Production of ketone bodies from acetyl-CoA to
counteract low blood [glucose]