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
- Familial hypercholesterolemia
- Myocardial Infarction (Heart Attack)
- Ischaemic stroke
Related
- Lipoprotein metabolism
- LDL receptor
- Apolipoprotein B (ApoB-100 and ApoB-48)
- PCSK9
- VLDL (very-low-density lipoprotein)
- Cholesterol
- 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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: LDL: The "Bad" Cholesterol: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); LDL clearance (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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Representative model, for educational purposes only.