Can anyone please tell about slope function

Jayakumar, R via methods%40net.bio.net (by R.Jayakumar from roswellpark.org)
Mon Mar 21 10:42:25 EST 2011


Hmmmm!! the protein concentrations are on the X-axis and OD on the Yaxis.  Always dependent variables on the Y-axis. 
Jay


________________________________________
From: methods-bounces from oat.bio.indiana.edu [methods-bounces from oat.bio.indiana.edu] On Behalf Of WS [novalidaddress from nurfuerspam.de]
Sent: Monday, March 21, 2011 8:19 AM
To: methods from magpie.bio.indiana.edu
Subject: Re: Can anyone please tell about slope function

Dear Sudheer,

the slope is the "m" in your equation. In real life, colorimetric
protein measurement standard curves sometimes get a bit far from
linear, so in times of computerized curve fits by eg excel,
sigma{plot, stat} or openoffice.org, you might be better off with a
2nd order fit (y=ax2 + bx + c); simply plot the OD readings on the x-
axis and the protein standard concentrations on the y-axis, then
you'll get directly the formula to calculate actual concentrations
from the OD values when performing a regression analysis.

By having a look at the R value you may compare various regression
methods (like linear vs 2nd order) and determine which one fits the
situation better.

BTW, the linear approximation is just an approximation which fits most
needs and is easily done when you have just a ruler and a sheet of
paper (when one wouldn't want to apply for mainframe computing time
just for a protein determination :). The chemistry that converts
protein into color is not really linear in respect of dose/response.

Have fun!

Wo
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