calculating the cell density

D.K. dk at no.email.thankstospam.net
Sat Oct 6 20:46:33 EST 2001


mukherji at tifr.res.in (Sulakshana Mukherjee) wrote:
>Dear all,
>I am following a protocol for making competent cells. In this protocol I
>am unable to understand the following step:
> " Determine the OD at 550 by diluting a small portion (e.g.,1%) of the
>cell suspension 300x. Then adjust the volume of the concentrated cell
>slurry with cold EWB(10% glycerol in ultrapure water) to produce a final
>OD at 550 of 200-250 units/ml." 

It asks you to measure cell density in your stock (determined as optical
units of absorbance), and dilute it to give ~250 optical units/ml final. 
Thus, if N times dilution of your suspension gives you reading A at 550 nm
(as long as A < 2), you will need to dilute it (N*A/250) times to get
desired final concentration. 

DK




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