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CENTRIFUGE SPEED


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8 replies to this topic

#1 josh_student

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Posted 14 January 2010 - 02:25 AM

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 !!!

#2 molgen

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Posted 14 January 2010 - 02:59 AM

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.

#3 josh_student

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Posted 14 January 2010 - 03:42 AM

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... ????

#4 gogreen

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Posted 14 January 2010 - 05:24 AM

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...

#5 mdfenko

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Posted 14 January 2010 - 12:03 PM

First, you have the molecular weight. The heavier something is the less time it needs to pellet.


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

talent does what it can
genius does what it must
i used to do what i got paid to do


#6 phage434

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Posted 14 January 2010 - 06:37 PM

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

#7 josh_student

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Posted 14 January 2010 - 08:58 PM

Thank u all for takin time n clearin my doubts

All were helpful....

#8 rhombus

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Posted 16 January 2010 - 09:26 AM

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.

#9 array75

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Posted 18 January 2010 - 07:52 AM

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!




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