Biochemistry · Topic
Centrifugation and ultracentrifugation !
Spinning a sample very fast pushes heavier or denser particles to the bottom first. It separates blood cells, organelles and lipoproteins.
Updated 2026-11-01
Key facts
- Centrifugal force (relative centrifugal force, ×g) makes particles sediment according to their size, shape and density.
- Routine lab: separating serum or plasma from cells, and the haematocrit (packed cell volume) in a spun capillary tube.
- Differential centrifugation of a cell homogenate, at rising speeds: nuclei → mitochondria (and lysosomes, peroxisomes) → microsomes (ER fragments) → ribosomes; the supernatant is the cytosol.
- Ultracentrifugation (The Svedberg, Nobel Prize 1926) separates macromolecules; the sedimentation coefficient is measured in Svedberg units (S): ribosomes 70S/80S, subunits 30S+50S and 40S+60S.
- Lipoproteins are classified by density in the ultracentrifuge: chylomicrons (lightest, float) < VLDL < IDL < LDL < HDL (densest, most protein).
In detail
- 1. Sedimentation rate depends on particle mass, shape and density relative to the medium; S values are not additive (30S + 50S = 70S).
- 2. Density-gradient centrifugation (sucrose or caesium chloride) separates particles that differ little in density; the Meselson–Stahl experiment used it to show semiconservative DNA replication.
- 3. Isopycnic (equilibrium) centrifugation: each particle stops where the gradient density equals its own.
- 4. Lipoprotein density rises with protein content and falls with triglyceride content; chylomicrons and VLDL float, giving the creamy layer of lipaemic serum.
- 5. The refrigerator test: plasma left overnight at 4 °C shows a creamy top layer with chylomicrons and a turbid lower layer with VLDL.
- 6. Clinical centrifuges spin at a few thousand g; ultracentrifuges reach several hundred thousand g under vacuum and refrigeration.
- Also called
- Svedberg unit (S), Differential centrifugation, Density gradient
Clinical notes
- A low haematocrit on a spun tube shows anaemia; a high one shows polycythaemia or dehydration.
- Lipaemic samples (very high triglycerides) can interfere with many tests; high-speed centrifugation clears them.
- Platelet-rich plasma and blood components (red cells, plasma, platelets) for transfusion are prepared by centrifugation.
Related conditions
Related
- Lipoprotein metabolism
- Chylomicron
- VLDL (very-low-density lipoprotein)
- LDL (low-density lipoprotein)
- HDL (high-density lipoprotein)
- Chromatography
- Cell organelles and their metabolism
- Ribosome (and the antibiotics that target it)
Test yourself
Think of the answer, then tap the question to see it.
In differential centrifugation of liver cells, which fraction sediments first?
The nuclei (with unbroken cells), at the lowest speed; mitochondria, then microsomes and ribosomes need higher speeds.
Why do the 40S and 60S subunits make an 80S ribosome rather than 100S?
Svedberg units measure sedimentation rate, which depends on shape and mass, so they are not additive.
What is the order of the lipoproteins from lowest to highest density?
Chylomicrons < VLDL < IDL < LDL < HDL; density rises as the protein share increases.
What does the haematocrit measure?
The fraction of blood volume made of packed red cells after the sample is centrifuged.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: The Svedberg – Facts - NobelPrize.org (NobelPrize.org (Nobel Prize Outreach), 2026); Hematocrit: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 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.