LECTURE 5 - GLUCONEOGENESIS + CORI CYCLE

Question 1

a dysregulation of which enzymes would cause a fructose intolerance?

Answer 1

fructokinase
fructose-1-phosphate aldolase

Question 2

what are all the options that G6P can become?

Answer 2

• can be converted back to glucose
• can be made into glycogen
• can be made into Ribose-5-phosphate through the PPP
• can be made into pyruvate to then into glycolysis

Question 3

why is glutathione reductase important and what does it rely on?

Answer 3

is the enzyme in the salvaging reaction which converts GSSH to GSH
this enzyme depends on NADPH, which is why NADPH is needed by every cell to prevent damage by oxidation

Question 4

what is gluconeogenesis?

Answer 4

biosynthesis of new glucose from non carbohydrate sources

Question 5

when is gluconeogenesis needed?

Answer 5

dietary glucose is not available
exhaustion of intracellular glucose
glycogen pool in liver is depleted
blood glucose levels are about to below normal

Question 6

where does gluconeogenesis occur?

Answer 6

in the liver (major) and in the kidney (minor)

Question 7

what are the substrates of gluconeogenesis?

Answer 7

lactate
pyruvate
intermediates from the CAC
amino acids (muscle)
NOT from fatty acids (but their breakdown generates ATP)

Question 8

what is the starting point of gluconeogenesis?

Answer 8

oxaloacetate (an intermediate of CAC)

Question 9

what steps does gluconeogenesis share with glycolysis?

Answer 9

the two processes share their reversible steps

Question 10

what enzymes are required by the irreversible steps of gluconeogenesis?

Answer 10

pyruvate carboxylase
PEPCK
FBPase
glucose-6-phosphatase

Question 11

where is glucose-6-phophatase found?

Answer 11

in the liver only

Question 12

what does gluconeogenesis consume/require?

Answer 12

requires NADH and requires ATP/GTP

(makes sense, its the reverse of glycolysis)

Question 13

what does PEPCK stand for?

Answer 13

phosphoenolpyruvate carboxykinase

Question 14

what are the pyruvate carboxylase and PEPCK reactions?

Answer 14

make phosphoenolpyruvate (PEP)
pyruvate carboxylase: carboxylation
PEPCK: decarboxylation

Question 15

what do pyruvate carboxylase and PEPCK require?

Answer 15

pyruvate (from amino acid catabolism)
energy, ATP (from catabolism of fatty acids)
acetyl-CoA (from catabolism of fatty acids), which is an allosteric activator!!

Question 16

how are the enzyme reactions of pyruvate carboxylase and PEPCK coupled?

Answer 16

pyruvate carboxylase uses ATP to make a high energy intermediate from pyruvate: oxaloacetate
the exergonic decarboxylation of oxaloacetate provides the energy for making PEP

Question 17

when does the cori cycle happen?

Answer 17

happens in absence of O2 and abundance of lactate, because in anaerobic conditions glucose becomes lactate

Question 18

what does the cori cycle regenerate?

Answer 18

regenerates NAD+ which is needed for glycolysis

Question 19

where does the cori cycle happen

Answer 19

muscle, liver (and most cells)

Question 20

what happens to pyruvate and NADH in no oxygen conditions?

Answer 20

pyruvate and NADH in the muscle become L-Lactate and NAD+

Question 21

what then happens to the L-lactate and the NAD+?

Answer 21

transporters efflux L-lactate into the bloodstream, and NAD+ replenishes the NAD+ pool to continue glycolysis

Question 22

so what is the cori cycle

Answer 22

lactate goes from the muscle to the liver, through the bloodstream
in the liver lactate is converted back into glucose, and glycolysis can continue

Question 23

pathways of glucose

Answer 23

Question 24

how would these pathways be different in the presence of oxygen?

Answer 24

Question 25

how would these pathways be different in the absence of oxygen?

Answer 25

Question 26

how would these pathways be different in cell division?

Answer 26

Question 27

how would these pathways be different in low blood sugar conditions?

Answer 27

Question 28

what is the enzyme responsible for the reversible reaction of pyruvate to lactate or vice versa?

Answer 28

lactate dehydrogenase