Biochemistry CAC

Does pyruvate enter the citric acid cycle directly?

No. Pyruvate is first converted to acetyl-CoA by the pyruvate dehydrogenase complex.

What does pyruvate become before entering the cycle?

Acetyl-CoA

What comes out when pyruvate becomes acetyl-CoA?

NADH and CO2

What molecule combines with acetyl-CoA to start the cycle?

Oxaloacetate

What is the first product formed when acetyl-CoA enters the cycle?

Citrate

What is the order of the citric acid cycle?

Citrate → Isocitrate → alpha-ketoglutarate → Succinyl-CoA → Succinate → Fumarate → Malate → Oxaloacetate

What comes after citrate?

Isocitrate

What comes after isocitrate?

alpha-ketoglutarate

What comes after alpha-ketoglutarate?

Succinyl-CoA

What comes after succinyl-CoA?

Succinate

What comes after succinate?

Fumarate

What comes after fumarate?

Malate

What comes after malate?

Oxaloacetate

How many carbons are in oxaloacetate?

4

How many carbons are in acetyl-CoA?

2

How many carbons are in citrate?

6

How many carbons are in isocitrate?

6

How many carbons are in alpha-ketoglutarate?

5

How many carbons are in succinyl-CoA?

4

How many carbons are in succinate, fumarate, malate, and oxaloacetate?

4

What is the carbon pattern of the cycle?

4 + 2 = 6 → 6 → 5 → 4 → 4 → 4 → 4 → 4

What enzyme converts oxaloacetate + acetyl-CoA to citrate?

Citrate synthase

What enzyme converts citrate to isocitrate?

Aconitase

What enzyme converts isocitrate to alpha-ketoglutarate?

Isocitrate dehydrogenase

What enzyme converts alpha-ketoglutarate to succinyl-CoA?

alpha-ketoglutarate dehydrogenase

What enzyme converts succinyl-CoA to succinate?

Succinyl-CoA synthetase

What enzyme converts succinate to fumarate?

Succinate dehydrogenase

What enzyme converts fumarate to malate?

Fumarase

What enzyme converts malate to oxaloacetate?

Malate dehydrogenase

What comes out at the isocitrate dehydrogenase step?

NADH and CO2

What comes out at the alpha-ketoglutarate dehydrogenase step?

NADH and CO2

What comes out at the succinyl-CoA synthetase step?

GTP

What comes out at the succinate dehydrogenase step?

FADH2

What comes out at the malate dehydrogenase step?

NADH

At which steps is CO2 released in the cycle?

Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase

At which steps is NADH produced in the cycle?

Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase

At which step is FADH2 produced?

Succinate dehydrogenase

At which step is GTP produced?

Succinyl-CoA synthetase

What is the output order in the cycle?

NADH, NADH, GTP, FADH2, NADH

Which citric acid cycle steps are irreversible?

Citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase

Is the citrate synthase step reversible or irreversible?

Irreversible

Is the aconitase step reversible or irreversible?

Reversible

Is the isocitrate dehydrogenase step reversible or irreversible?

Irreversible

Is the alpha-ketoglutarate dehydrogenase step reversible or irreversible?

Irreversible

Is the succinyl-CoA synthetase step reversible or irreversible?

Reversible

Is the succinate dehydrogenase step reversible or irreversible?

Reversible

Is the fumarase step reversible or irreversible?

Reversible

Is the malate dehydrogenase step reversible or irreversible?

Reversible

What is the overall purpose of the citric acid cycle?

To oxidize acetyl-CoA, release CO2, make NADH, FADH2, and GTP, and regenerate oxaloacetate

What are the net products of one turn of the citric acid cycle?

3 NADH, 1 FADH2, 1 GTP, 2 CO2

What are the total products if you include pyruvate dehydrogenase before the cycle?

4 NADH, 1 FADH2, 1 GTP, 3 CO2 per pyruvate

What molecule is regenerated at the end of the cycle?

Oxaloacetate

Which step adds water?

Fumarate → Malate by fumarase

Which step uses CoA again after citrate is formed?

alpha-ketoglutarate → succinyl-CoA