pellets in centrifugation--densities of different cell parts

[thebillsfan]

ive looked around the internet for a listing of relative densities of the different parts of a cell and couldnt find any. i've had a few passages about centrifugation and a question or two along the lines of ... "the first pellet will contain what?" i dont really think there's an intuitive way to understand the relative densities of cell parts--its just something you have to know. could anyone shed light on this?

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[RogueUnicorn]

just think big=dense. e.g. nucleus, mitochondria etc will pellet out before ribosomes, which is before proteins, followed by plasmids.. etc etc

the question "first pellet contains what" would really depend on your centrifuge conditions, you can pellet out EVERYTHING in a single spin if you wanted to... i'd imagine the answer to such questions is strongly implied in the passage

 

[thebillsfan]

hmm...i have in my notes from the EK books that:

Centrifugations: high density ribosomes are at the bottom, low density mito/lysosomes remain at the top.

I'd agree that organelles would be more dense, so I'm not sure why i have ribosomes as more dense. Could be an EK error?

 

[RogueUnicorn]

no i could see how ribosomes are more dense. i was essentially guessing with that one. however, my understanding of centrifugation is that the separation is based on size & mass