Metabolism: Gylcolysis

Question 1

Draw the structure of D-glucose.

Answer 1

[Answer]

Question 2

Draw the structure of D-fructose.

Answer 2

[Answer]

Question 3

Draw the structure of pyruvate.

Answer 3

[Answer]

Question 4

Where does glycolysis occur?

Answer 4

cytoplasm of the cell

Question 5

What happens during the energy investment phase of glycolysis?

Answer 5

During the energy investment phase, two ATP molecules are used to phosphorylate glucose, converting it into two molecules of glyceraldehyde-3-phosphate.

Question 6

What happens during the energy payoff phase of glycolysis?

Answer 6

During the energy payoff phase, the two molecules of G3P are converted into pyruvate, producing four ATP molecules and two NADH molecules.

Question 7

What happens in the first step of glycolysis?

Answer 7

The first step is the phosphorylation of glucose by hexokinase, using one ATP to form glucose-6-phosphate.
[Diagram 1] [Diagram 2]

Question 8

What happens in the second step of glycolysis?

Answer 8

Glucose-6-phosphate is converted into fructose-6-phosphate by the enzyme phosphoglucose isomerase.
[Diagram 1] [Diagram 2]

Question 9

What is the third step of glycolysis?

Answer 9

Fructose-6-phosphate is phosphorylated by phosphofructokinase-1 (PFK-1), using one ATP to form fructose-1,6-bisphosphate.
[Diagram 1] [Diagram 2]

Question 10

What happens in the fourth step of glycolysis?

Answer 10

Fructose-1,6-bisphosphate is split into two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P) by the enzyme aldolase.
[Diagram 1] [Diagram 2]

Question 11

What is the fifth step of glycolysis?

Answer 11

Dihydroxyacetone phosphate (DHAP) is converted into glyceraldehyde-3-phosphate (G3P) by triose phosphate isomerase.
[Diagram 1] [Diagram 2]

Question 12

What happens in the sixth step of glycolysis?

Answer 12

Glyceraldehyde-3-phosphate (G3P) is oxidized and phosphorylated by glyceraldehyde-3-phosphate dehydrogenase, producing 1,3-bisphosphoglycerate and NADH.
[Diagram 1] [Diagram 2]

Question 13

What is the seventh step of glycolysis?

Answer 13

1,3-bisphosphoglycerate donates a phosphate group to ADP, forming ATP and 3-phosphoglycerate, catalyzed by phosphoglycerate kinase.
[Diagram 1] [Diagram 2]

Question 14

What happens in the eighth step of glycolysis?

Answer 14

3-phosphoglycerate is converted into 2-phosphoglycerate by the enzyme phosphoglycerate mutase.
[Diagram 1] [Diagram 2]

Question 15

What is the ninth step of glycolysis?

Answer 15

2-phosphoglycerate is dehydrated by enolase to form phosphoenolpyruvate (PEP).
[Diagram 1] [Diagram 2]

Question 16

What happens in the tenth step of glycolysis?

Answer 16

Phosphoenolpyruvate (PEP) donates a phosphate group to ADP, forming ATP and pyruvate, catalyzed by pyruvate kinase.
[Diagram 1] [Diagram 2]

Question 17

What is the net yield of ATP and NADH from glycolysis?

Answer 17

The net yield from glycolysis is 2 ATP molecules and 2 NADH molecules per molecule of glucose.

Question 18

List differences between hexokinase and glucokinase.

Answer 18

(1) Hexokinase is found in all tissues, whereas glucokinase is primarily found in the liver.

(2) Hexokinase has a high affinity (low Km) for glucose, meaning it can efficiently phosphorylate glucose even at low concentrations. Glucokinase on the other hand, has a low affinity for glucose (high Km), meaning it is active only when glucose levels are high, such as after a meal.

(3) Hexokinase can phosphorylate a variety of hexoses, including glucose, fructose and galactose, whereas glucokinase is specific to glucose.

(4) Hexokinase is inhibited by its product, glucose-6-phosphate, which helps regulate its activity based on the cell’s energy needs, Glucokinase is not inhibited by G6P; instead it is regulated by insulin and glucose levels, allowing it to ploay a key role in blood glucose regulation.