R 4 KREBS

Question 1

Overview of KREBS

Answer 1

The Krebs cycle (sometimes called the citric acid cycle) consists of a series of enzyme-controlled reactions

2 carbon (2C) Acetyl CoA enters the circular pathway from the link reaction in glucose metabolism

Acetyl CoA formed from fatty acids (after the breakdown of lipids) and amino acids enters directly into the Krebs Cycle from other metabolic pathways

4 carbon (4C) oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form the 6 carbon (6C) citrate

Coenzyme A is released in this reaction
Citrate is then converted back to oxaloacetate through a series of oxidation-reduction (redox) reactions

Question 2

what does krebs regenerate

Answer 2

Regeneration of Oxaloacetate

Question 3

How is Oxaloacetats regenerated

Answer 3

Oxaloacetate is regenerated in the Krebs cycle through a series of redox reactions

Question 4

FIRST STEP OF KREBS

Answer 4

Decarboxylation of citrate
Releasing 2 CO2 as waste gas

Question 5

STEP 2 of KREBS

Answer 5

Oxidation (dehydrogenation) of citrate
Releasing H atoms that reduce coenzymes NAD and FAD
3 NAD and 1 FAD → 3NADH + H+ and 1 FADH2

Question 6

STEP 3 OF KREBS

Answer 6

Substrate-linked phosphorylation
A phosphate is transferred from one of the intermediates to ADP, forming 1 ATP

Question 7

Exam tip

Answer 7

The Krebs cycle is often referred to as cyclical or circular. This is because the acceptor molecule oxaloacetate is regenerated throughout the reaction so that it can start all over again by adding another acetyl CoA. You may be asked to name the important molecules in the Krebs cycle like oxaloacetate. It is also worth noting how the number of carbon atoms in the substrate molecule changes as the cycle progresses.