CENTRIFUGE SPEED - (Jan/14/2010 )

Dear All,


I have this very basic question..... How do u know or how is the centrifugation speeds and time are set for different molecules ??? Why is it different for DNA n RNA n PROTEINS ?? Also comment on the significance of the centrifugation duration....

Thanks in advance !!!

First, you have the molecular weight. The heavier something is the less time it needs to pellet.
Second, you can substitute speed and duration. i.e. if your centrifuge can't get up to the right speed you can increase the duration in the same proportion.

Thanks 4 d reply !

Let me ask u 1 straight forward question....

Why do v pellet rna only at 10000 rpm for 15 mins after the iso propanol precipitation ??
what will happen if it is say, 15000 rpm for 25 mins or so... ????

I guess nothing happens more than the RNA getting pelleted!! I always use 14000 rpm and sometimes do the spin for 30 min when I have other stuff to look at...

molgen on Jan 14 2010, 05:59 AM said:

density is more important than molecular weight when it comes to pelleting.

Depending on your tube, you may end up with no sample, a cracked tube, and a wet centrifuge rotor.

Thank u all for takin time n clearin my doubts

All were helpful....

AGAIN !!!!!!!!!!!


The SI unit for centrifuge speed is Relative Centrifugal Force (RCF) or G.

RPM means nothing.......rotor diameter is different in every centrifuge.


G is constant and is always used in scientific papers.


Kindest regards.


Rhombus.

Normally, the DNA/ RNA should survive up to 20.000 g or 30.000 g - as already mentioned, it is much more important if the tube survives the g-force.
The higher the g-force, the more more material can be precipitated. For example, the supernatant of a 5.000g-run should result in a further (much smaller) pellet when centrifuged with 30.000 g.

Rhombus is totally right, the info "10.000 rpm" needs at least the exact rotor type with the radius - better to use the g-value!