Lecture 5 - Citric Acid Cycle

What is the citric acid cycle (CAC)?

pathway that oxidises acetyl coa to produce co2, fadh2, nadh and gtp or atp

Where does the CAC occur in eukaryotic cells?

mitochondrial matrix

Where does the CAC occur in bacteria?

cytosol

What is the role of NADH and FADH2?

carries electrons to oxidative phosphorylation

What happens to pyruvate during pyruvate oxidation?

loses a carbon to co2, oxidized and produces nadh

What happens to the remaining 2-carbon acetyl group?

joins coenzyme a to form acetyl coa

What does pyruvate dehydrogenase (PDH) do?

catalyses pyruvate into acetyl coa

What are the products of pyruvate oxidation per pyruvate?

acetyl coa, nadh, co2

What is the role of thiamine (vitamin B1) in pyruvate oxidation?

forms tpp, helps remove co2 from pyruvate

What happens in step 1 of the CAC?

acetyl coa combines with oxaloacetate to form citrate

Which enzyme catalyses step 1?

citrate synthase

What happens in step 2 of the CAC?

citrate rearranged by removing and re adding water to form isocitrate

Which enzyme catalyses step 2?

aconitase

What happens in step 3 of the CAC?

isocitrate oxidised, produces co2 and nadh, forms a ketoglutarate

Which enzyme catalyses step 3?

isocitrate dehydrogenase

What happens in step 4 of the CAC?

a ketogluturate oxidized, producing co2, nadh, succinyl coa

Which enzyme catalyses step 4?

a ketogluturate dehydrogenase

What happens in step 5 of the CAC?

succinyl coa converted into succinate, producing gtp or atp

Which enzyme catalyses step 5?

succinyl CoA synthetase

What happens in step 6 of the CAC?

succinate oxidized to fumarate, fad reduced to fadh2

Which enzyme catalyses step 6?

succintae dehydrogenase

What happens in step 7 of the CAC?

water added to fumarate to form malate

Which enzyme catalyses step 7?

fumurase

What happens in step 8 of the CAC?

malate oxidized into oxaloacetate, producing nadh

Which enzyme catalyses step 8?

malate dehydrogenase

Why is oxaloacetate important?

starts the cycle and regenerated at the end

What is substrate-level phosphorylation in the CAC?

direct production of gtp or atp during conversion of succinyl coa to succinate

What are the products of one turn of the CAC per acetyl-CoA?

2 co2, 3 nadh, 1 fadh2, 1 gtp or atp

What are the combined products of pyruvate oxidation and the CAC per glucose?

6 co2, 8 nadh, 2 fadh2, 2 gtp or atp

What does amphibolic mean?

pathway functions in catabolism and anabolism

How do high ATP and high NADH affect the CAC?

slow the cycle because enough energy

What is product inhibition of PDH?

acetyl coa inhibits pdh, reducing furthur conversion of pyruvate

How does calcium affect the CAC?

stimulates isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, increasing cycle activity