Krebs Cycle

Question 1

Other name for Krebs cycle:

Answer 1

Citric acid cycle

Question 2

Where is the Krebs cycle situated in aerobic respiration?

Answer 2

• After glycolysis and link reaction

Question 3

When does Krebs cycle take place?

Answer 3

• Mitochondrial matrix

Question 4

What is the role of the Krebs cycle?

Answer 4

• Processes acetyl CoA to prepare for oxidative phosphorylation

Question 5

For each acetyl CoA molecule, the Krebs cycle produces?

Answer 5

• 2 CO2 molecules as by-product
• Electron carriers, including 3 molecules of reduced NAD and one molecule of reduced FAD -> for oxidative phosphorylation
• One molecule of ATP through substrate-level phosphorylation

Question 6

Sequence of enzymatic reactions in the Krebs cycle?

Answer 6

1. Acetyl CoA (2C acetate) merges with a 4C molecule, OAA, to create a 6C molecule, citrate.
2. Citrate is decarboxylated, releasing 2 molecules of CO2.
3. Citrate is also dehydrogenated (oxidised), releasing hydrogens that reduce three molecules of NAD and one molecule of FAD.
4. For each acetyl CoA that enters the cycle, one ATP (or GTP in some organisms) is synthesised directly via substrate-level phosphorylation
5. Oxaloacetate is regenerated for the next turn of the cycle.

Question 7

Coenzymes in Krebs cycle:

Answer 7

• NAD
• FAD
• Coenzyme A

Question 8

Role of coenzymes in Krebs cycle?

Answer 8

• Oxidising agents -> accept electrons and protons and become reduced themselves
• Reduced coenzymes later donate these gained electrons to the electron transport chain

Question 9

Differences between NAD and FAD:

Answer 9

• NAD accepts one electron and one proton when it is reduced, FAD accepts 2 protons and 2 electrons when reduced
• NAD participates in all stages of respiration, while FAD only accepts protons and electrons in Krebs cycle
• NAD results in synthesis of 3 ATP molecules, FAD results in synthesis of 2 ATP molecules

Question 10

Importance of Krebs cycle:

Answer 10

• It oxidises and breaks down large nutrients into smaller ones, like carbon dioxide, which can be removed as a waste product
• It generates reduced NAD and reduced FAD, which carry protons and electrons into oxidative phosphorylation
• It continually regenerates the 4C molecule to combine with acetyl CoA molecules
• Provides a variety of immediate compounds required for the biosynthesis of essential cellular components such as fatty acids, amino acids and chlorophyll