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# 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)
- 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

- [Familial chylomicronemia syndrome (lipoprotein lipase deficiency)](https://durgical.com/en/conditions/familial-chylomicronemia-syndrome/)
- [Iron deficiency anaemia](https://durgical.com/en/conditions/iron-deficiency-anaemia/)

## Related

- [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/)
- [Chylomicron](https://durgical.com/en/biochemistry/topics/chylomicron/)
- [VLDL (very-low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/vldl/)
- [LDL (low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/ldl/)
- [HDL (high-density lipoprotein)](https://durgical.com/en/biochemistry/topics/hdl/)
- [Chromatography](https://durgical.com/en/biochemistry/topics/chromatography/)
- [Cell organelles and their metabolism](https://durgical.com/en/biochemistry/topics/cell-organelles-and-their-metabolism/)
- [Ribosome (and the antibiotics that target it)](https://durgical.com/en/biochemistry/enzymes/ribosome/)

## 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

## What does the haematocrit measure?

The fraction of blood volume made of packed red cells after the sample is centrifuged.

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

Sources: [The Svedberg – Facts - NobelPrize.org](https://www.nobelprize.org/prizes/chemistry/1926/svedberg/facts/) (NobelPrize.org (Nobel Prize Outreach), 2026); [Hematocrit: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003646.htm) (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.

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