Cell fractionation and Ultracentrifugation.

Pg 41/42 in AQA Bio textbook. (They're the ones we use at QE, so if you're from there, that bit of info is for you.)

Obj- To describe the process and the resultant separation of cell components.

Cell fractionation is where cells are broken up and the organelles they contain are separated out.

1. HOMOGENATION: The cell is broken up by a homogeniser (big spinny thing, bit like a food liquidiser, only a little bit more high-tech. xP) The resultant fluid is called homogenate.
2. ULTRACENTRIFUGATION: Fragments of the homogenate are separated. rganelles get sedimented and seperated in order of density. (Not heaviness. Exam board people don't like heaviness. :D)

The three conditions of the whole thing are:

1. Temperature: Really low to prevent bacterial growth, but the main reason is to slow down any enzymes that may damage the organelles.
2. Isotonic Solution: Makes sure it has the same water protentail as the tissue to preven organelles from bursting or shrinking.
3. Buffered: Maintains a constant pH (Why???? )

The solid pellet at the bottom are centrifugation is called a supernatant.

It goes down a density gradient, For example: Nucleus, Mitochondria, Lysosomes, Membrane, Ribosomes.

The faster it is spun in centrifugation, the lighter the organelles that get separated/isolated, so it is spun with gradually increasing speed to get the denser ones first.

This is useful for finiding out the function, but not 100% perfect.

And remeber, correct me where I'm wrong. It helps. (:

-Nin.