Glycolysis

Question 1

Step 1

Answer 1

Conversion of glucose to glucose-6-phosphate

Hexokinase in the tissues or glucokinase in the liver catalyses this reaction.
The kinase enzyme catalyses the transfer of a phosphoryl group from ATP to glucose and ADP as well as glucose-6-phosphate are produced. This is in the presence of Mg2+.

This is the first irreversible step of glycolysis.

Question 2

Step 2

Answer 2

Isomerisation of glucose-6-phosphate to fructose-6-phosphate

Phosphohexose isomerase catalyses this reaction. This is in the presence of Mg2+.

Question 3

Step 3

Answer 3

Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate

Phosphofructokinase (PFK-1) catalyses this reaction. Seeing as another phosphoryl group is being added, ATP is required and ADP is produced. The product is fructose-1,6-bisphosphate. Mg2+ is needed as a cofactor.

This is the second irreversible step of glycolysis and it is the rate limiting step.

Question 4

Step 4

Answer 4

Cleavage of fructose-1,6-bisphosphate

The enzyme catalyses this is aldolase. This cuts the molecule in half and dihydroxyacetone phosphate and glyceraldehyde-3-phosphate are produced (DHAP and GA-3-P).

Question 5

Step 5

Answer 5

Conversion of DHAP to GA-3-P

Triose phosphate isomerase catalysis this reaction.

Question 6

Step 6

Answer 6

Oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate

Glyceraldehyde-3-phosphate dehydrogenase is used to catalyse this reaction. NAD is reduced to NADH + H+. Inorganic phosphate is added to GA-3-P so ATP is not used.

Question 7

Step 7

Answer 7

Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate

Phosphoglycerate kinase is used to catalyse this reaction. The phosphoryl group from 1,3-bisphosphoglycerate is transferred to ADP and ATP is produced. 3-phosphoglycerate is the outcome. Mg2+ is a cofactor.

Question 8

Step 8

Answer 8

Mutase reaction converting 3-phosphoglycerate to 2-phosphoglycerate

Phosphoglycerate mutase catalyses this reaction. The enzyme catalyses the transfer of a phosphoryl group within the same molecule. Mg2+ is a cofactor.

Question 9

Step 9

Answer 9

Dehydrate 2-phosphglycerate to phosphoenolpyruvate (PEP)

Enolase is the enzyme that catalyses this (water is removed).

Question 10

Step 10

Answer 10

Conversion of PEP to Pyruvate

Pyruvate kinase is the enzyme catalyses this. PEP transfers a phosphoryl group to ADP to produce ATP and pyruvate. Mg2+ and K+ are used as cofactors.

This the third irreversible step of glycolysis.

Question 11

What can you say about the energies of each step?

Answer 11

It is important to note that all the steps that involve ATP in glycolysis have a negative deltaG’ and that all the other steps are positive.