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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# LDL (low-density lipoprotein)

LDL delivers cholesterol to the tissues; when there is too much in the blood it settles in the arteries, hence the name "bad" cholesterol.

Updated 2026-11-01

## Key facts

- It is the end product of VLDL; each particle has one ApoB-100 and a cholesteryl ester core.
- It carries most plasma cholesterol.
- The LDL receptor clears it, mainly in the liver; ApoB-100 is the ligand.
- High LDL causes atherosclerosis: lowering it reduces heart attacks and strokes.

## In detail

- LDL binds its receptor in clathrin-coated pits and enters by endocytosis.
- In the acidic endosome it detaches from the receptor, which returns to the membrane.
- In the lysosome ApoB is degraded and cholesteryl ester is hydrolysed to free cholesterol.
- Free cholesterol slows HMG-CoA reductase and receptor synthesis (SREBP-2) and is stored after esterification by ACAT (SOAT).
- LDL trapped in the artery wall is oxidised; macrophages take it up through unregulated scavenger receptors and become foam cells.

## Clinical notes

- LDL targets depend on each person's cardiovascular risk.
- An LDL of 190 mg/dL or more in an adult suggests familial hypercholesterolaemia.
- Lp(a) is LDL with apolipoprotein(a) attached; raised Lp(a) is inherited and increases cardiovascular risk.

## Related conditions

- [Atherosclerosis and dyslipidaemia](https://durgical.com/en/conditions/atherosclerosis-and-dyslipidaemia/)
- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)
- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)

## Related

- [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/)
- [LDL receptor](https://durgical.com/en/biochemistry/enzymes/ldl-receptor/)
- [Apolipoprotein B (ApoB-100 and ApoB-48)](https://durgical.com/en/biochemistry/enzymes/apolipoprotein-b/)
- [PCSK9](https://durgical.com/en/biochemistry/enzymes/pcsk9/)
- [VLDL (very-low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/vldl/)
- [Cholesterol](https://durgical.com/en/biochemistry/molecules/cholesterol/)
- [HMG-CoA reductase](https://durgical.com/en/biochemistry/enzymes/hmg-coa-reductase/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which LDL ligand does its receptor recognise?

ApoB-100.

## What does the cholesterol released from LDL do inside the cell?

It slows HMG-CoA reductase and LDL receptor synthesis, and the excess is esterified for storage.

## How does a foam cell form?

A macrophage takes up oxidised LDL through unregulated scavenger receptors and fills with cholesterol.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [LDL: The "Bad" Cholesterol: MedlinePlus](https://medlineplus.gov/ldlthebadcholesterol.html) (MedlinePlus, US National Library of Medicine, 2026); [LDL clearance (R-HSA-8964038)](https://reactome.org/PathwayBrowser/#/R-HSA-8964038) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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