5.6.3 Krebs Cycle

Question 1

Where in the mitochondria does the Krebs cycle take place?

Answer 1

• Mitochondrial matrix.

Question 2

What reactions take place in the Krebs cycle?

Answer 2

• Oxidation and reduction.

Question 3

What are the products of the Krebs cycle and where are they used?

Answer 3

• Carbon dioxide - waste
• NADH - stage 4 oxidative phosphorylation
• FADH - stage 4 oxidative phosphorylation
• ATP - substrate level phosphorylation.

Question 4

What is the significance of the Krebs cycle?

Answer 4

• Produces hydrogen atoms that are carried by NADH and FADH to the ETC for oxidative phosphorylation.
• Regenerates 4C molecule that combines with acetyl coenzyme A.
• Other respiratory substrates include the breakdown products of lipids and amino acids which enter the Krebs cycle.

Question 5

Describe how reduced coenzymes and carbon dioxide are made in the Krebs cycle? (6)

Answer 5

Two acetyl molecules forms two citrate molecules. Two citrate molecules forms an intermediate 5C compound where two NADH molecules are formed from two NAD and carbon dioxide leaves the Krebs cycle. The 5C compound forms two oxaloacetate molecules where another carbon dioxide molecule leaves the Krebs cycle and ADP is converted into ATP. Four NAD molecules are converted to NADH and two FAD molecules are converted to two FADH molecules.