Citric Acid Cycle

Question 1

Where is Acetyl CoA formed and what from

Answer 1

Pyruvate / Fatty Acids oxidised into Acetyl CoA in mitochondrial matrix

Question 2

How is Acetyl CoA made?

Answer 2

Pyruvate with Pyruvate Dehydrogenase

-> Decarboxylation of Pyruvate, oxidation, transfer of CoA complex
produces CO2 and NADH

Question 3

Process of Acetyl CoA production

Answer 3

• Pyruvate decarboxylation attaching to TPP, creating CO2 & hydroxyethyl TPP
• Hydroxyethyl transferred to oxidised lipoyllysine forming acetyl lipoyllysine
• CoA-SH attaches to acetyl group, reducing lipoyllysine and making Acetyl CoA
• FAD uptakes hydrogens + electrons, forming FADH2
• NAD+ recycles FADH2 forming NADH + H+ & FADH2 -> FAD

Question 4

Citric Acid Cycle steps, products, enzymes (8)

Answer 4

• Oxaloacetate (C4) accepts Acetyl residue (C2) forming Citrate (C6) [Condensation] {Citrate Synthase}
• Citrate -> Isocitrate [Hydration + Dehydration] {Aconitase}
• Isocitrate -> alpha-Ketoglutarate [Oxidative decarboxylation] {Isocitrate dehydrogenase}
• alpha-Ketoglutarate -> Succinyl CoA [Oxidative decarboxylation] {alpha-Ketoglutarate dehydrogenase complex}
• Succinyl CoA -> Succinate [Substrate-level Phosphorylation] {Succinyl-CoA synthetase}
• Succinate -> Fumarate [Dehydrogenation] {Succinate dehydrogenase}
• Fumarate -> Malate [Hydration] {Fumarase}
• Malate -> Oxaloacetate [Dehydrogenation] {Malate dehydrogenase}

Question 5

Enzymes that can control entry of Citric Acid Cycle

Answer 5

• Pyruvate Dehydrogenase
• Isocitrate Dehydrogenase
• alpha-Ketoglutarate Dehydrogenase

Question 6

Pyruvate Dehydrogenase is regulated by

Answer 6

Negative Regulators: Increase Acetyl CoA, NADH, ATP, reduced NAD+
Positive Regulators: Increase Pyruvate, ADP

Question 6

Pyruvate Dehydrogenase is regulated by

Answer 6

Negative Regulators: Increase Acetyl CoA, NADH, ATP, reduced NAD+
Positive Regulators: Increase Pyruvate, ADP

Question 7

Isocitrate Dehydrogenase is regulated by

Answer 7

Negative Regulators: Increase ATP, NADH

Positive Regulators: Increase ADP