Metabolism 3

Question 1

When and where does glycolysis take place?

Answer 1

Anaerobic process that occurs in the cytoplasm of the cell.

Question 2

What is the first step of glycolysis?

Answer 2

Glucose is phosphorylated by hexokinase to glucose-6-phosphate. Virtually irreversible reaction that traps the glucose inside the cell.
- 1 ATP molecule is used

Question 3

What is the second step of glycolysis?

Answer 3

Glucose-6-phosphate undergoes isomerisation to fructose-6-phosphate by phosphoglucose isomerase.

Question 4

Why is glucose-6-phosphate isomerised to fructose-6-phosphate?

Answer 4

Allows efficient splitting of molecules later on.

Question 5

What is the third step of glycolysis?

Answer 5

Fructose-6-phosphate is phosphorylated by phosphofructokinase to form fructose-1,6-bisphosphate.
- 1 ATP molecule is used

Question 6

What is the fourth step of glycolysis?

Answer 6

The fructose-1,6-bisphosphate ring is opened up by aldolase to form glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

Question 7

What is the fifth step of glycolysis?

Answer 7

Dihydroxyacetone phosphate is then isomerised to glyceraldehyde-3-phosphate by triose phosphate isomerase.

Question 8

What is the sixth step of glycolysis?

Answer 8

The two molecules of glyceraldehyde-3-phosphate are combined together to form 1,3-bisphosphoglycerate by using glyceraldehyde-3-phosphate dehydrogenase.

Question 9

What is the seventh step of glycolysis?

Answer 9

1,3-biphosphoglycerate is dephosphorylated and one phosphate group is transferred to ADP to form ATP using phosphoglycerate kinase.
- 1 ATP molecule is produced.

Question 10

What is the eighth step in glycolysis?

Answer 10

Phosphate group is shuffled from 3-position to 2-position using phosphoglycerate mutase.

Question 11

What is the ninth step of glycolysis?

Answer 11

2-phosphoglycerate is dehydrated using enolase to form phosphoenolpyruvate.
- 1 H2O is removed.

Question 12

What is the final step of glycolysis?

Answer 12

Phosphoenolpyruvate is dephosphorylated to pyruvate using pyruvate kinase.
- 1 ATP molecule is produced.

Question 13

What are the end products of glycolysis?

Answer 13

• 2 NADH molecules (used in oxidative phosphorylation)
• 2 ATP
• 2 pyruvate

Question 14

What does lactate dehydrogenase do?

Answer 14

Catalyses the interconversion of pyruvate and lactate, with elevated levels of LDH suggesting a stroke, heart attack, muscle injury or liver disease.

Question 15

Where is LDH found?

Answer 15

Liver, heart, skeletal muscle, brain, blood and lung.

Question 16

What are the three possible fates for pyruvate?

Answer 16

• Alcohol fermentation
• Lactate production (LDH) which occurs in anaerobic conditions and can be used to regenerate NADH
• Generation of acetyl-CoA through link reaction

Question 17

What is the pyruvate dehydrogenase complex and what happens?

Answer 17

A step that commits the pyruvate from glycolysis into the citric acid cycle.

• Pyruvate is decarboxylated (to a 2C species)
• CoA added
• NAD regenerated

Question 18

Where does the link reaction take place?

Answer 18

Mitochondrial matrix

Question 19

What are the three enzymes involved in the link reaction?

Answer 19

• Lipoamide reductase-transacetylase
• Dihydrolipoyl dehydrogenase
• Pyruvate decarboxylase

Question 20

What are the five co-factors involved in the link reaction?

Answer 20

• Thiamine pyrophosphate
• Lipoamide
• FAD
• Coenzyme A
• NAD+