L6 glycolysis and gluconeogenesis

Question 1

how is NAD+ regenerated to allow glycolysis to continue?

Answer 1

• aerobically: in mitochondria
• pyruvate to lactate releases 1 NAD+

NB - NAD/NADH+ can not cross mitochondrial membrane so shuttled in aerobic conditions.

Question 2

fates of lactate?

Answer 2

• converts back into pyruvate to enter TCA (if O2 present)

- converts back to glucose via gluconeogenesis (in the muscle)

Question 3

what can be a substrate for gluconeogenesis?

Answer 3

Amino acids

• “glucogenic” (18-20AA)
• “Nonglucogenic” leucine and lysine
• pyruvate (glycolysis)
• lactate (glycolysis)
• glycerol (from stored fats)
• oxaloacetate (from TCA)

Question 4

can fat enter gluconeogenesis?

Answer 4

No

• Straight chains with even number of carbon
• even numbered fatty acid oxidation cannot be converted to oxaloacetate or any other mediate of gluconeogenesis

(exception: if fatty acid has odd number of carbon)
GLYCEROL CAN ENTER

Question 5

where does glycerol enter gluconeogenesis?

Answer 5

glycerol converted to G-3-P, dehydrogenised to Dihydroxyacetone phosphate

Question 6

how is glycolysis and gluconeogenesis regulated by ATP levels?

Answer 6

Low ATP (high AMP):

• AMP stimulates glycolysis to produce ATP
• AMP inhibits gluconeogenesis (to conserve energy and stop futile cycles)

High ATP (low AMP):

• ATP inhibits glycolysis
• citrate and ACoA stimulate gluconeogenesis

Question 7

how does fructose-2-6-bisphosphate regulate glycolysis/gluconeogrenesis?

Answer 7

• synthesised by PFK2 from F-6-P
• broken down by FBPase2
• Stimulates glycolysis
• inhibits gluconeogenesis

Question 8

how does insulin regulate glycolysis/gluconeogrenesis?

Answer 8

• inhibits FBPase2 (increase in F-2,6-BP)
• glycolysis stimulated
• gluconeogenesis inhibited

Question 9

how does glucagon regulate glycolysis/gluconeogrenesis?

Answer 9

• inhibits PFK2 (less F-2,6-BP)
• activates FBPase2 (less F-2,6-BP)
• less glycolysis
• more gluconeogenesis