Citric Acid Cycle

What are the 8 steps of the citric acid cycle with the enzymes and details

1. oxaloacetete → citrate

   1. enzyme: citrate synthase

   2. irreversible/committed step

   3. cleavage of thioester bond powers reaction

2. citrate → isocitrate

   1. enzyme: aconitase

   2. isomerization reaction

3. isocitrate → alpha ketoglutarate

   1. enzyme: isocitrate dehydrogenase

   2. first oxidative decarboxylation

   3. yields: NADH + 1CO2

4. alpha ketoglutarate → succinyl CoA

   1. enzyme: alpha ketoglutarate dehydrogenase complex

   2. second oxidative decarboxylation

   3. yields: 1NADH + 1CO2

5. succinyl coA → succinate + ATP

   1. succinyl coA synthetase

   2. substrate-level phosphorylation

   3. yield: 1 ATP or GTP

6. succinate → fumarate

   1. succinate dehydrogenase

   2. yield: 1 FADH2

7. fumarate → malate

   1. enzyme: fumarase

   2. H2O added (hydration)

8. malate → oxaloacetate

   1. enzyme: malate dehydrogenase

   2. yield: 1 NADH

What is the total energy yield per 1 molecule of Acetyl CoA?

3 NADH, 1 FADH2, and 1 ATP (via substrate-level phosphorylation).

What are the two primary control points (enzymes) within the CAC?

Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase.

What are the common inhibitors of the Citric Acid Cycle?

ATP and NADH (high energy signals).

What are the common activators of the Citric Acid Cycle?

ADP (low energy signal) and Pyruvate.

Which reaction replenishes the cycle if its components are used for biosynthesis?

The Pyruvate Carboxylase reaction, which converts Pyruvate + CO2 + ATP into Oxaloacetate. This is activated by Acetyl CoA.

Which biosynthetic pathways use CAC intermediates as precursors?

* Citrate: Fatty acids and sterols. alpha-Ketoglutarate: Glutamate and other amino acids/purines.Succinyl Co

What do both stages of the citric acid cycle generate

high-energy electrons that are used to power the synthesis of ATP in oxidative phosphorylation

What are the two key control points in the citric acid cycle

• isocitrate dehydrogenase

• alpha ketoglutarate dehydrogenase complex

What are the negative and positive effectors of pyruvate going to acetyl coA

• negative: ATP, acetyl coA, and NADH

• positive: ADP and pyruvate

what are the negative and positive effectors for isocitrate dehydrogenase complex

• negaitve: ATP and NADH

• positive: ADP

What are the negative effectors of the alpha ketoglutarate dehydrogenase complex

ATP, succinyl coA, and NADH