18.3 The Krebs Cycle Flashcards
Where does the Krebs cycle take place? (1 mark)
Mitochondrial matrix
What does each cycle of the Krebs cycle result in? (1 mark)
The breakdown of an acetyl group.
Describe the Krebs cycle. (6 mark)
- AcetylcoenzymeA delivers an acetyl group to the Krebs cycle (from the link reaction).
- The acetyl group combines with oxaloacetate to form citric acid.
- The citric acid goes through decarboxylation and dehydration, forming a 5C compound.
- The 5C compound undergoes further decarboxylation and dehydration reactions, eventually forming oxaloacetate.
- The cycle begins again
What delivers the acetyl group to the Krebs cycle? (1 mark)
AcetlycoenzymeA (from the link reaction)
What does the acetyl group combine with and produce? (2 marks)
The acetyl group combines with oxaloacetate to produce citric acid.
Name three things released (and what they produce) between the 5C compound and forming oxaloacetate. (4 marks)
Energy, which allows substrate level phosphorylation to happen.
H2, which reduces FAD to FADH2.
H which reduces NAD to NADH.
What is substrate level phosphorylation? (2 marks).
The formation of ATP without the involvement of an electron transport chain/ involving the transfer of a phosphate group from a short-lived, highly reactive intermediate.
Why are coenzymes important in respiration? (1 mark)
They transfer protons, electrons, and functional groups between the reactions.
Compare NAD and FAD. (4 marks)
N: In all stages of cellular respiration
F: Only in the Krebs cycle
N: Accepts one hydrogen
F: Accepts two hydrogens
N: Is oxidised at the start of the electron transport chain
F: Is oxidised further along the electron transport chain.
N: Results in the synthesis of 3 ATP moleucles
F: Results in the synthesis of 2 ATP molecules
What are NAD and FADH2 later used for? (1 mark)
In oxidative phosphorylation.
