# Explain how acetyl-CoA links the products of glycolysis to the Krebs cycle, including the fate of carbon atoms and the significance of the coenzyme involved.

> IB DP Biology Higher Level (2023 syllabus) — C1.2 Cell respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. Pyruvate (from glycolysis) is converted to acetyl-CoA during pyruvate oxidation / the link reaction, which occurs in the mitochondrial matrix.
2. One carbon atom is removed as CO₂ (decarboxylation), so the two-carbon acetyl group is transferred to CoA to form acetyl-CoA.
3. The acetyl group is donated to oxaloacetate (a four-carbon compound) to form citrate (a six-carbon compound), entering the Krebs cycle.
4. CoA is regenerated / released and is significant because it acts as a carrier molecule that can accept another acetyl group, allowing continuous entry of acetyl groups into the Krebs cycle; also, NAD⁺ is reduced to NADH during pyruvate oxidation, providing reducing power for the electron transport chain.

## Key terms

- [acetyl-CoA](https://www.gradenine.co.uk/glossary/acetyl-coa)
- [Krebs cycle](https://www.gradenine.co.uk/glossary/krebs-cycle)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-acetyl-coa-links-the-products-9c403075) · Published by Druglandscape Ltd.