Anaerobic Metabolism

Question 1

What is the only way of producing energy without oxygen and mitochondria?

Answer 1

Glycolysis

Question 2

Where does glycolysis take place in the cell?

Answer 2

In the cytosol

Question 3

What is the net production of glycolysis?

Answer 3

From 1 molecule of glucose (6C):

• Loss of 2 x ATP
• Gain of 2 x Pyruvate (3C)
• Reduction of 2 x NAD to NADH

Question 4

Describe the 1st step of Glycolysis

Answer 4

Hexokinase uses ATP to phosphorylate Glucose into Glucose-6-P.

This reaction is irreversible and traps Glucose inside the cell.

Hexokinase is regulated through inhibition when the concentration of Glucose-6-P increases.

Question 5

Describe the 2nd step of Glycolysis

Answer 5

Phosphohexoisomerase converts Glucose-6-P to Fructose-6-P

Question 6

Describe the 3rd step of Glycolysis

Answer 6

Phosphofructokinase *uses* *ATP* to phosphorylate Fructose-6-P into Fructose 1,6-biphosphate.

This reaction is irreversible.

Phosphofructokinase is inhibited by high levels of intracellular ATP

Question 7

Describe the 4th step of Glycolysis

Answer 7

Aldolase splits Fructose 1,6-biphosphate into Glyceraldehyde 3-P (3C) and Dihydroxyacetone phosphate (3C)

Question 8

Describe the 5th step of Glycolysis

Answer 8

Dihydroxyacetone phosphate can be converted to glyceraldehyde 3-P by Triose Phosphate Isomerase.

Question 9

Describe the 6th step of Glycolysis

Answer 9

2 x Glyceraldehyde 3-P is oxidised to 2 x 1,3-bisphosphoglycerate by Glyceraldehyde 3-P Dehydrogenase.

2 x NAD+ is reduced to 2 x NADH

Question 10

Describe the 7th step of Glycolysis

Answer 10

2 x 1,3-bisphosphoglycerate is dephosphorylated by Phosphoglycerate Kinase to form 2 x 3-Phosphoglycerate and 2 x ATP (substrate-level phosphorylation)

Question 11

Describe the 8th step of Glycolysis

Answer 11

2 x 3-phosphoglycerate is converted to

2 x 2-phosphoglycerate by Phosphoglycerate mutase

Question 12

Describe the 9th step of Glycolysis

Answer 12

2 x 2-phosphoglycerate is converted into 2 x Phosphoenolpyruvate by Enolase

Question 13

Describe the 10th step of Glycolysis

Answer 13

2 x Phosphoenolpyruvate is dephosphorylated by Pyruvate Kinase to form 2 x Enolpyruvate and 2 x ATP

The 2 x Enolpyruvate is rapidly and non-enzymatically converted to form 2 x Pyruvate

This causes the former reaction to be irreversible.

Question 14

Give an overview of the process of Glycolysis and the net products per molecule of Glucose.

Answer 14

2 x Pyruvate

2 x ATP (2 ATP loss, 4 ATP gained)

2 x NADH

Question 15

Name the 3 enzymes in glycolysis that are regulated.

Answer 15

1. Hexokinase
2. Phosphofructokinase
3. Pyruvate Kinase

Question 16

What is the problem in anaerobic conditions and how it rectified in the short term?

Answer 16

In anaerobic conditions such as ischaemia, prolonged exercise and the lack of mitochondria, there is insufficient oxygen to re-oxidise NADH to NAD+, which is required in the early stages of glycolysis.

This is rectified by the reduction of pyruvate to lactate with the simultaneous oxidation of cytosolic NADH to NAD+ by Lactate Dehydrogenase, allowing glycolysis to continue.

The lactate is transported to the liver and used to synthesize glucose - ‘Gluconeogenesis’.

This requires ATP and thus oxygen is required once aerobic conditions are restored - ‘Oxygen Debt’