Centrifugation uses centrifugal force to separate particles and macromolecules based on density differences. A centrifuge spins liquid samples at high speeds, causing denser particles to sediment to the bottom while less dense materials remain above. There are two main types - laboratory centrifuges for small volumes, using rotors to spin tubes at 1,000-15,000 rpm, and preparative centrifuges for larger volumes in continuous processes at 500-2,000 rpm. Ultracentrifuges spin at extremely high speeds like 30,000 rpm for analytical and preparative applications.

1. Centrifugation A centrifuge is used to separate particles or even macromolecules: -Cells -Sub-cellular components -Proteins -Nucleic acids Basis of separation: -Size -Shape -Density Methodology: -Utilizes density difference between the particles/macromolecules and the medium in which these are dispersed -Dispersed systems are subjected to artificially induced gravitational fields

2. Densities of biological material Material Density (g/cm 3 ) Microbial cells 1.05 - 1.15 Mammalian cells 1.04 - 1.10 Organelles 1.10 - 1.60 Proteins 1.30 DNA 1.70 RNA 2.00

9. Preparative centrifugation (A)

10. Preparative centrifugation r a r t Q z (B)

11. Preparative centrifugation Dividing (A) by (B) and integrating: