18.3 Krebs cycle

Question 1

Where does the Krebs cycle occur?

Answer 1

Mitochondrial matrix

Question 2

Similarly to the previous stages, what 3 reactions does the Krebs cycle include?

Answer 2

Oxidative decarboxylation, dehydrogenation and substrate level phosphorylation

Question 3

What happens to the H atoms released during the Krebs cycle?

Answer 3

They’re accepted by NAD coenzymes and FAD

Question 4

What is the by-product of the Krebs cycle?

Answer 4

CO2

Question 5

What are the produced reduced NAD + FAD used for?

Answer 5

Final step of aerobic respiration, oxidative phosphorylation, to produce large quantities of ATP by chemiosmosis

Question 6

What are the 3 stages of the Krebs cycle?

Answer 6

1. Acetyl CoA delivers an acetyl group. The 2-C acetyl combines w/ 4-C oxaloacetate to form 6-C citrate (citric acid)
2. Citric acid undergoes dexarboxylation + dehydrogenation to form 5-C compound. One reduced NAD and CO2 is produced
3. The 5-C compound undergoes more decarboxylation and dehydrogenation. 1 Co2, 2 Reduced NAD 1 reduced FAD are produced, and 1 ATP is produced by substrate-level phosphorylation. Oxaloacetate is eventually regenerated.

Question 7

What is the function of coenzymes in respiration?

Answer 7

To transfer protons and electrons between the reactions

Question 8

What are the 4 differences between coenzymes NAD and FAD?

Answer 8

1. NAD takes part in all stages of respiration, FAD only takes part in hydrogen acceptance in Krebs cycle
2. NAD only accepts 1 H whereas FAD accepts 2 H
3. NAD is oxidised at the start of the electron transport chain, FAD is oxidised further along the electron transport chain
4. Reduced NAD results in synthesis of 3 ATP whereas Reduced FAD results in synthesis of 2 ATP