5.7.5 The Link Reaction

Question 1

What is the link reaction?

Answer 1

The end product of glycolysis is pyruvate

Pyruvate contains a substantial amount of chemical energy that can be further utilised in respiration to produce more ATP

When oxygen is available pyruvate will enter the mitochondrial matrix and aerobic respiration will continue

Pyruvate moves across the double membrane of the mitochondria via active transport
It requires a transport protein and a small amount of ATP

It is referred to as the link reaction because it links glycolysis to the Krebs cycle

Question 2

What are the steps of the link reaction?

Answer 2

The steps are:
Pyruvate is oxidised by enzymes to produce acetate, CH3CO(O)- and carbon dioxide, requiring the reduction of NAD to NADH
Combination with coenzyme A to form acetyl coenzyme A (acetyl CoA)

It produces:
Acetyl coA
Carbon dioxide (CO2)
Reduced NAD (NADH)

pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD

Question 3

What is the role of coenzyme A?

Answer 3

A coenzyme is a molecule that helps an enzyme carry out its function but is not used in the reaction itself

Coenzyme A consists of a nucleoside (ribose and adenine) and a vitamin

In the link reaction, CoA binds to the remainder of the pyruvate molecule (acetyl group 2C) to form acetyl CoA

It then supplies the acetyl group to the Krebs cycle where it is used to continue aerobic respiration

This is the stage that brings part of the carbohydrate (or lipid/amino acid) into the further stages of respiration and links the initial stage of respiration in the cytoplasm to the later stages in the mitochondria