Citric acid cycle

Where does the citric acid cycle occur?

Eukaryotes - mitochondrial matrix. Prokaryotes - cytoplasm

What molecule enters the citric acid cycle?

2 Acetyl-CoA’s

How many times does the citric acid cycle happen per glucose molecule?

Twice

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

3 NADH, 1 FADH₂, 2 CO2, and 1 ATP (or GTP)

How is ATP (or GTP) produced in the citric acid cycle?

By substrate-level phosphorylation.

What is the main purpose of the citric acid cycle?

To harvest high-energy electrons in NADH and FADH₂ for the electron transport chain.

How many NADH, FADH₂, and ATP/GTP molecules are produced per glucose molecule?

6 NADH, 2 FADH₂, and 2 ATP (or GTP).

Step 1

Oxaloacetate combines with acetyl-CoA to form citrate

Step 2

Citrate is oxidized and rearranged to eventually form α-ketoglutarate, producing 1 NADH and releasing 1 CO₂.

Step 3

α-ketoglutarate is oxidized to succinyl-CoA, producing 1 NADH and releasing 1 CO₂.

Step 4

Succinyl-CoA is converted to succinate, producing 1 ATP (or GTP) by substrate-level phosphorylation.

Step 5

Succinate is oxidized to fumarate, producing 1 FADH₂.

Step 6

Fumarate converted to malate

Step 7

Malate is oxidized to oxaloacetate, producing 1 NADH

How is the citric acid cycle regulated?

Feedback inhibition

When is NADH produced?

Citrate → α-Ketoglutarate, α-Ketoglutarate → Succinyl-CoA, Malate → Oxaloacetate

When is CO2 released?

Citrate → α-Ketoglutarate, α-Ketoglutarate → Succinyl-CoA

When is ATP produced?

Succinyl-CoA → Succinate

When is FADH2 produced?

Succinate → Fumarate