Fatty Acid Synthesis vs Beta-Oxidation

Fatty Acid Synthesis vs Beta-Oxidation: Key Differences

By StudyStore · Published 2026-11-05 · 1 min read · 218 words

Fatty acid synthesis builds palmitate from acetyl-CoA in the fed state. Beta-oxidation breaks fatty acids down to acetyl-CoA in the fasting state. They are not simple reverses of each other.

Comparison

	Synthesis	Beta-oxidation
Location	Cytosol	Mitochondrial matrix
Carrier	Acyl carrier protein (ACP)	CoA
Redox cofactor	Uses NADPH	Makes NADH and FADH₂
Carbon unit	Malonyl-CoA adds 2 carbons	Removes 2 carbons as acetyl-CoA
Key enzyme	Acetyl-CoA carboxylase (ACC), then fatty acid synthase	Carnitine acyltransferase I
Hormone	Insulin activates	Glucagon and epinephrine activate
End product	Palmitate (16C)	Acetyl-CoA

Regulation link

Malonyl-CoA, made by ACC, inhibits carnitine acyltransferase I. When synthesis is on, newly made fatty acids are not shuttled into the matrix to be burned. ACC is activated by citrate and insulin, and inhibited by AMPK and glucagon.

Getting acetyl-CoA out

Acetyl-CoA cannot cross the inner mitochondrial membrane. It leaves as citrate, which is cleaved in the cytosol by ATP-citrate lyase.

Common traps

Placing both in the mitochondria. Synthesis is cytosolic.
Giving synthesis NADH. It uses NADPH.
Forgetting malonyl-CoA. It is the switch between the two pathways.

One-minute recap

Synthesis: cytosol, NADPH, ACP, insulin.
Oxidation: matrix, NADH and FADH₂, CoA, glucagon.
Malonyl-CoA blocks fatty acid entry to the matrix.

Check yourself: 5-question mini-quiz

Try each question first, then click it to reveal the answer.

1. Where does fatty acid synthesis occur?

The cytosol.

2. Which cofactor does synthesis use as reductant?

NADPH.

3. What does malonyl-CoA inhibit?

Carnitine acyltransferase I.

4. How does acetyl-CoA reach the cytosol?

As citrate, cleaved by ATP-citrate lyase.

5. Which hormone favors synthesis?

Insulin.

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Written by StudyStore from standard scientific facts. Study aid only. Always check values against the reference your exam provides.