Advanced Topic 1009 of 1102 Biochemistry, Environment & Industry

Krebs Cycle

A cycle oxidizing acetyl-CoA to CO2 producing NADH, FADH2 and ATP.

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In-depth explanation of Krebs Cycle

The Krebs cycle, also called the citric acid cycle, takes place in the mitochondrial matrix and completely oxidises acetyl-CoA to carbon dioxide. Acetyl-CoA combines with oxaloacetate to form citrate, and a series of eight enzyme-catalysed steps releases two CO2 per turn while regenerating oxaloacetate. Each turn produces three NADH, one FADH2 and one GTP, which is readily converted to ATP. The reduced carriers feed electrons into the electron transport chain, so the cycle is the central hub of aerobic energy extraction. Intermediates such as alpha-ketoglutarate and succinyl-CoA also serve as starting points for amino acid and heme synthesis.

Going deeper: Krebs Cycle

Key ideas: Acetyl-CoA (2C) combines with oxaloacetate (4C) to give citrate (6C). Per acetyl-CoA, one turn releases 2 CO2 and makes 3 NADH, 1 FADH2 and 1 GTP or ATP. Per glucose it turns twice. Occurs in the mitochondrial matrix, and pyruvate is first converted to acetyl-CoA with release of CO2 and NADH.

Common mistakes and connections: Students say oxygen is used directly in the cycle; it is only needed to reoxidize NADH and FADH2 later, so the cycle stops without oxygen. Count per glucose: double all per-turn numbers. Links to oxidative phosphorylation and to biosynthesis, since intermediates feed amino acid synthesis.

Visualization of Krebs Cycle

Products of one turn of the Krebs cycle. The reduced carriers NADH and FADH2 carry electrons onward to the electron transport chain. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Each turn of the cycle releases two CO2 molecules while producing three NADH, one FADH2 and one GTP.

Frequently asked questions about Krebs Cycle

What is Krebs Cycle?

A cycle oxidizing acetyl-CoA to CO2 producing NADH, FADH2 and ATP.

Is Krebs Cycle a beginner, intermediate or advanced topic?

Krebs Cycle is a advanced topic in Biochemistry, Environment & Industry. It builds on beginner and intermediate topics, so review those first if needed.

What should I learn before Krebs Cycle?

Study these earlier topics in Biochemistry, Environment & Industry first: Metabolism, ATP, Glycolysis.

What comes after Krebs Cycle?

The next topics in Biochemistry, Environment & Industry are Oxidative Phosphorylation and Photosynthesis.

Can I practise Krebs Cycle with quizzes?

Yes. The interactive lesson includes a self-check question on Krebs Cycle, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.

Where Krebs Cycle fits in Biochemistry, Environment & Industry

Krebs Cycle is topic 34 of 127 in Biochemistry, Environment & Industry.