Reactions of Glycolysis

Question 1

Glycolysis: Step 1

Glucose is Phosphorylated

What enzyme is involved?

Answer 1

Glucose is phosphorylated by Hexokinase to produce Glucose-6-phosphate using

• ATP provides the phosphate and is converted to ADP
• Phosphorylation traps glucose inside the cell, allowing glucose to continue to move into the cell even against its concentration gradient.

Question 2

Glycolysis: Step 2

Glucose 6-phosphate to Fructose 6-phosphate

What enzyme is involved?

Answer 2

Phosphoglucose isomerase convers Glucose-6-phosphate→Fructose-6-phosphate

Question 3

Glycolysis: Step 3

Fructose 6-phosphate is Phosphorylated

What enzyme is involved?

Answer 3

•Product is a bisphosphate (2 separate phosphates)

Fructose-6-phosphate is phosphoylated →Fructose 1,6-bisphosphate by phosphofructo kinase

•ATP provides the phosphate and becomes ADP.

Question 4

Glycolysis: Step 4

Fructose 1,6-bisphosphate is Split in Two

What enzyme is involved?

Answer 4

Fructose bisphosphate aldose cleaves Fructose 1,6-bisphosphate to generate two 3C molecules→ Dihydroxyacetone phosphate (DHAP) + Glyceraldehyde-3-phosphate (GAP)

Question 5

Glycolysis: Step 5

Conversion of DHAP to GAP

What enzyme is involved?

Answer 5

Glyceraldehyde 3-phosphate dehydrogenase adds free inorganic phosphate in a redox reaction to produce 1,3-bisphosphoglycerate

•At equilibrium 96% is DHAP.

–The DHAP is converted into GAP by triose phosphate isomerase and using up GAP pulls across the equilibrium to generate more GAP.

Question 6

Glycolysis: Step 6

GAP to 1,3-BPG

What enzyme is involved?

Answer 6

Glyceraldehyde 3-phosphate dehydrogenase adds free inorganic phosphate (not from ATP) in a redox reaction to produce 1,3-bisphosphoglycerate GAP is oxidised and NAD+ is reduced to NADH

Question 7

Glycolysis: Step 7

Formation of 3-phosphoglycerate

What enzyme is involved?

Answer 7

Phosphoglycerate kinase phosphoylates ADP→ATP (thereby removing a phosphate from 1,3-bisphosphoglycerate to produce 3-Phosphoglycerate

Finally yields ATP!

This step generates 2 ATP as there ate two 3C units feeding into it

Question 8

Steps 8-10

Formation of 3-phosphoglycerate

What enzyme is involved?

Answer 8

• Phosphoglycerate mutase rearranges 3-Phosphoglycerate to produce 2-phosphoylcerate
• Enolase condenses 2-phosphoylcerate to produce Phosphoenolpyruvate (PEP) with the loss of H₂O
• Pyruvate kinase converts Phosphoenolpyruvate (PEP) to pyruvate by using the phosphate group from Phosphoenolpyruvate to convert ADP→ATP

Question 9

What is the Net reaction of glycolysis?

Answer 9

Glucose + 2 Pi + 2 ADP + 2 NAD⁺

→2 pyruvate + 2 ATP + 2 NADH + 2 H⁺ + 2 H₂O

Net gain in NADH which must be oxidised by metabolism of pyruvate.

Question 10

What are the 3 main fates of pyruvate?

Answer 10

• Fermentation to ethanol e.g. in yeast.
• Conversion by lactate dehydrogenase e.g. in muscle
• Conversion to acetyl CoA.