Gluconeogenesis

Question 1

state what it is meant by the key term - gluconeogenesis

Answer 1

gluconeogenesis is a metabolic pathway in which glucose is synthesised from non-carbohydrate precursors

Question 2

where does gluconeogenesis occur ?

Answer 2

occurs mainly in the liver, and to a lesser extent, in the kidney

Question 3

where are gluconeogenic enzymes located ?

Answer 3

gluconeogenic enzymes are located in the cytosol, mitochondria, and the ER

Question 4

state 2 facts about the following statement:

‘non-carbohydrate precursors are converted to pyruvate or other precursors’

Answer 4

1. lactate and alanine are converted to pyruvate

2. glycerol is converted to dihydroxyacetone phosphate (DHAP)

Question 5

state the reaction of how lactate is converted to pyruvate

Answer 5

lactate + NAD+ ——–lactate dehydrogenase——> pyruvate + NADH + H+

Question 6

state the reaction of how alanine is converted to pyruvate

Answer 6

alanine + alpha-ketoglutarate—–aminotransferase——> pyruvate + glutamine

Question 7

state the 2 reactions of how glycerol is converted to DHAP

Answer 7

1. glycerol + ATP ——glycerol kinase——–> glycerol-3-phosphate + ADP
2. glycerol-3-phosphate + ATP + NAD+ ——–glycerol phosphate dehydrogenase——-> dihydroxyacetone phosphate + NADH + H+

Question 8

explain ‘pyruvate shuttling in and out of the mitochondria’ in gluconeogenesis (5 points)

Answer 8

1. pyruvate enters mitochondrion
2. pyruvate carboxylase catalyses the formation of oxaloacetate
3. oxaloacetate can’t exit as no transporter
4. converted to malate and transported into cytosol by malate transporter
5. converted back to oxaloacetate by malate dehydrogenase

Question 9

when is ATP not re-synthesised in gluconeogenesis

Answer 9

ATP is not re-synthesised during steps 3 and 1 (reverse to glycolysis) as is thermodynamically unfeasible

Question 10

explain ‘glucose-6-phosphate shuttling in and out of the ER’ in gluconeogenesis

Answer 10

1. T1 transports glucose-6-phosphate into ER lumen
2. SP (stabilising protein) binds Ca2+ which is required by G6Pase
3. G6Pase catalyses G6P —> glucose
4. T2 transports Pi into the cytosol
5. T3 transports glucose into the cytosol

Question 11

what is the first step in gluconeogenesis ?

Answer 11

pyruvate —–pyruvate carboxylase—–> oxaloacetate

oxaloacetate ——phosphoenolpyruvate carboxylase—– phosphoenolpyruvate

Question 12

what is the second step in gluconeogenesis ?

Answer 12

phosphoenolpyruvate ——-enolase——-> 2, phosphoglycerate

Question 13

what is the third step in gluconeogenesis ?

Answer 13

2, phosphoglycerate —–phosphoglycerate mutase——> 3, phosphoglycerate

Question 14

what is the fourth step in gluconeogenesis ?

Answer 14

3, phosphoglycerate —–phosphoglycerate kinase——> 1,3 diphosphoglycerate

Question 15

what is the fifth step in gluconeogenesis ?

Answer 15

1,3 diphosphoglycerate ——glyceraldehyde phosphate dehydrogenase——> glyceraldehyde-3-phosphate

Question 16

what is the sixth and seventh step in gluconeogenesis ?

Answer 16

glyceraldehyde-3-phosphate —— triose phosphate isomerase —-> dihydroxyacetone phosphate

glyceraldehyde-3-phosphate—–aldolase——> fructose 1,3 bisphosphate

Question 17

what is the eighth step in gluconeogenesis ?

Answer 17

fructose 1,6 bisphosphate —–fructose 1,6 bisphosphatase——> fructose-6-phosphate

Question 18

what is the ninth step in gluconeogenesis ?

Answer 18

fructose-6-phosphate ——–phosphohexase isomerase——-> glucose-6-phosphate

Question 19

what is the tenth step in gluconeogenesis ?

Answer 19

glucose-6-phosphate ———-glucose-6-phosphatase——-> glucose