Lecture 26: Glycolysis

Question 1

Why is the conversion of pyruvate to lactate necessary?

Answer 1

The reduction to pyruvate to lactate allows for the recycling of NADH to NAD+ under anaerobic conditions, and thus for glycolysis and ATP production to continue

• NAD+ is required for glycolysis
• during vigorous exercise, the demand for ATP for muscle contraction exceeds the ability of the blood supply to provide oxygen and the conversion of glucose to lactate provides the only way to get ATP

Question 2

In the absence of oxygen what is pyruvate converted to ?

Answer 2

In the presence of oxygen each pyruvate is further oxidised (via acetyl-CoA) to produce 3CO2 in the CAC
In the absence of oxygen, pyruvate acts as an electron acceptor and is reduced to lactate, a reaction catalysed by the enzyme lactate dehydrogenase. This reaction results in the deoxidation NADH to NAD+

Question 3

Describe the reaction from pyruvate to acetyl-CoA

Answer 3

The conversion of pyruvate to acetyl-CoA is catalysed by a complex enzyme, pyruvate dehydrogenase.
- involves the loss of one of the three carbons of pyruvate as CO2 and the transfer of hydrogen to NAD+
pyruvate + NAD+ + CoA-SH ——> acetyl-CoA + NADH + H+ CO2

Question 4

What is substrate level phosphorylation?

Answer 4

1,3 bis-phosphorlycerate to generate at least two molecules of ATP. This occurs in two separate reactions, separated by a rearrangement reaction. Each is coupled is coupled to the synthesis of ATP

Question 5

Describe the phases of the glycolytic pathway?

Answer 5

Energy investment phase: phosphorylation of glucose and conversion to 2 molecules of glycerladehyde-3-phosphate
= requires 2 ATP
Energy payoff phase: conversion of glyceraldyde-3-phosphate to pyruvate and coupled formation of 4 molecules of ATP

Question 6

What is glycolysis ?

Answer 6

• splitting of glucose
• conversion of glucose 6C molecule to pyruvate 3C molecule
• energy is conserved in ATP and NADH
• pyruvate may be further metabolised aerobically or anaerobically

Question 7

What are the main steps of glycolysis ?

Answer 7

1. glucose 6C —-> pyruvate 3C. The split occurs at fructose-1,6-bisphosphate
2. 2ATP is required to initiate glucose molecule.
   3 2.NAD+ is converted to 2NADH
3. 4 ATP’s are produced so the net gain is 2 ATP’s per glucose