gluconeogenesis

Question 1

what is gluconeogenesis?

Answer 1

when glucose is formed from non carbohydrate substances such as lactate/glycerol/amino acids

Question 2

when do we use gluconeogenesis?

Answer 2

when we are fasting and the body has low blood sugar and the liver has already dispensed its glycogen

Question 3

where does gluconeogenesis occur?

Answer 3

in the liver mostly and a little in the kidneys, cytosol

Question 4

what is the starting substance of gluconeogenesis?

Answer 4

oxaloacetate

Question 5

name the enzymes that change pyruvate into PEP

Answer 5

pyruvate carboxylase and PEP carboxykinase

Question 6

what does pyruvate carboxylase do?

Answer 6

turns pyruvate and HCO-3 to oxaloacetate (needs ATP)

Question 7

what does PEP carboxykinase do?

Answer 7

converts oxaloacetate into PEP (using GTP)

Question 8

describe pyruvate carboxylase

Answer 8

is a tetramer and each subunit has a biotin molecule

Question 9

describe biotin

Answer 9

it acts as a CO2 carrier, by acquiring a carboxyl substitute as its ureido group.

Question 10

how is biocytin formed?

Answer 10

when a carboxyl group is bound to a ureido group by an amide link between its valeryl carboxyl group and the E-amino group of a lys side chain

Question 11

describe the 2 steps involved in the binding of a carboxyl group to biotin

Answer 11

1- biotin is carboxylated by a bicarbonate ion to dehydrate the bicarbonate. This releases CO2 which attaches to biotin.
2- the active carboxyl group is transferred from carboxybiotin to pyruvate to oxaloacetate

Question 12

can PEP leave the mitochondria?

Answer 12

yes through specific transfer membrane proteins

Question 13

how does oxaloacetate leave the mitochondria?

Answer 13

it must be converted to malate or aspartate

Question 14

how is oxaloacetate converted to malate?

Answer 14

by the enzyme Malate Dehydrogenase (uses NADH)

Question 15

how is oxaloacetate converted to aspartate?

Answer 15

by Aspartate Aminotransferase, (doesn’t use NADH) note that Aspartate can be converted to fumarate, which is hydrated to malate and then dehydrogenated to oxaloacetate

Question 16

what are the 3 irreversible reactions of glycolysis that gluconeogenesis reverses?

Answer 16

turning pyruvate back to PEP (using pyruvate kinase), turning fructose-1,6-biphosphate back to fructose-6-phosphate (using PFK) , turning glucose-6-phosphate back to glucose (using glucokinase)

Question 17

where is glucose-6-phosphatase present?

Answer 17

only in the liver and kidney

Question 18

what is the purpose of Fructose-2,6-biphosphate?

Answer 18

it is an allosteric effector, it activates PFK, and deactivates FBPase, it is synthesized by PFK-2

Question 19

glycogen breakdown is stimulated by?

Answer 19

phosphorylation

Question 20

when gluconeogenesis is activated what happens to glycolysis?

Answer 20

glycolysis is inhibited at the pyruvate kinase level by alanine and phosphorylation

Question 21

describe the cori cycle?

Answer 21

slow twitch muscle fibers produce lactate when ATP demand is unachievable. Lactate goes through blood stream to liver where it is turned into pyruvate by the enzyme lactate dehydrogenase. Then pyruvate turns into glucose using gluconeogenesis