5.7.6 The Krebs cycle

Question 1

What is the Kreb’s cycle also referred to as?

Answer 1

The citric acid cycle

Question 2

What does the krebs cycle consist of?

Answer 2

A series of enzyme-controlled reactions

Question 3

Where does the Krebs cycle take place?

Answer 3

In the matrix of the mitochondria

Question 4

What enters the circular pathway from the link reaction?

Answer 4

Acetyl coA

Question 5

What accepts the 2C acetyl fragment from acetyl coA?

Answer 5

4C oxaloacetate to form the 6C citrate
Coenzyme A is released in this reaction

Question 6

How is citrate converted back to oxaloacetate?

Answer 6

Through a series of oxidation-reduction (redox) reactions

Question 7

State the steps of the Krebs cycle

Answer 7

1. Acetyl group is accepted by oxaloacetate (4C) to form citrate (6C).
2. Decarboxylation of citrate occurs, releasing CO2 as a waste gas
3. Oxidation (dehydrogenation) of citrate releases H atoms that reduce coenzymes NAD and FAD, producing an intermediate 5C compound.
4. This 5C compound is decarboxylated and dehydrogenated to regenerate oxaloacetate. During this, substrate level phosphorylation occurs which is when a phosphate is transferred from one of the intermediates to ADP, forming 1 ATP

Question 8

Why is the Krebs cycle referred to as cyclical?

Answer 8

As the acceptor molecule oxaloacetate is regenerated throughout the reaction so that it can start all over again by adding another acetyl coA.