Metabolism 2 (Gluconeogenesis)

Question 1

Which steps aren’t in equilibrium in glycolysis?

Answer 1

1 = glucose into G-6-P

3 = F-6-P into Fructose 1,6-bisphosphate

10 = phosphoenolpyruvate into pyruvate

Question 2

What happens when there is no glucose around

(starvation/fasting)?

Answer 2

Gluconeogenesis

Question 3

What is gluconeogenesis?

Answer 3

A process via which glucose is synthesised from non-carbohydrate precursors:
>lactate
>alanine
>glycerol

Question 4

What are the non-carbohydrate precursors converted into?

Answer 4

Lactate –> pyruvate

Alanine –> pyruvate

Glycerol –> dihydroxyacetone phosphate (DHAP)

Question 5

Where does gluconeogenesis take placE?

Answer 5

Major extent = liver

Lesser extent = kidney

Question 6

Why isn’t gluconeogenesis the complete reversal of glycolysis?

Answer 6

The equilibrium of glycolysis lies far on the side of pyruvate formation
(favours conversion of glucose into pyruvate)

Question 7

What is the equation for converting glucose into G-6-P?

Answer 7

Glucose + ATP
—(via Hexokinase)–>
G-6-P + ADP

Question 8

What is the equation for converting F-6-P into Fructose-1,6-bisphosphate?

Answer 8

F-6-P + ATP

-(Phosphofructokinase)–>

Fructose-1,6-bisphosphate + ADP

Question 9

What is the equation for converting phosphoenolpyruvate into pyruvate?

Answer 9

Phosphoenolpyruvate + ADP

—(pyruvate kinase)–>

Pyruvate + ATP

Question 10

Describe the 1st of the 2 steps involved in converting pyruvate into phosphoenolpyruvate (PEP).

Answer 10

1. Pyruvate —> oxaolacetate

Catalysed by pyruvate carboxylase
- requires biotin + Mg2+

Uses ATP + CO2

Question 11

Describe the 2nd of the 2 steps involved in converting pyruvate into phosphoenolpyruvate(PEP).

Answer 11

2. Oxaloacetate —>
   PEP

Catalysed by PEP carboxykinase (PEPCK)
- uses GTP or ITP

(simultaneous decarboxylation & phosphorylation)

Question 12

What does GTP stand for?

What about ITP?

Answer 12

Guanosine triphosphate

Inosine triphosphate

Question 13

What are the 3 glycolysis enzymes replaced with in gluconeogenesis?

Answer 13

1. hexokinase replaced by G-6-Pase
2. Phosphofructokinase replaced by Fructose-1,6-bisphosphatase
3. Pyruvate kinase replaced by:
   >pyruvate carboxylase
   > phosphoenolpyruvate carboxykinase

Question 14

What is the equation for the conversion of Fructose-1,6-bisphosphate into F-6-P?

Answer 14

Fructose-1,6-bisphosphate

–(H2O + fructose-1,6-bisphosphatase)–>

F-6-P + Pi

Question 15

What is the equation for converting G-6-P into glucose?

Answer 15

G-6-P

–(G-6-Pase)–>

Glucose

(Carbon 6 removed)

Question 16

Which gluconeogenic enzymes aren’t found in the cytosol?

Where are they found?

Answer 16

Pyruvate carboxylase
= mitochondria

G-6-Pase
= endoplasmic reticulum

Question 17

Why must oxaloacetate be converted into another substance to be transported out the mitochondria?

What is this substance?

Answer 17

Neither liver nor kidney cells possess a protein for transporting oxaloacetate out mitochondria

Malate
via malate dehydrogenase

Question 18

Which transporter proteins enable movement of G-6-P?

What about glucose?

What about Pi?

What about malate?

Answer 18

T1

T3

T2

Malate-aspartate shuttle