Monday, August 17, 2009

Dancing with the molecules

Here are some things I learnt from chapter 3, of Biological Physics by Nelson.

Biological question: Why is the nanoworld so different from the macroworld?
Physical idea: Everything is (thermally) dancing.

Activation barriers control reaction rates.
i.e., the rate of a typical chemical reaction depends on temperature largely via a factor of exp(-Eb/k_B T) where the activation energy Eb is independent of temperature, characteristic of the reaction and usually of the order of an eV (10^{-19} J) . Note this energy scale is two orders of magnitude larger than k_B T. Knowing this helps understand why genetic information must be coded at the molecular level. (Schrodinger emphasized this in What is life? which heavily influenced James Watson).

Early in the twentieth century, T.H. Morgan performed a series of experiments on genetic linkage that led him to deduce that genetic factors (alleles) must be encoded in a linear sequence. By the 1940's there were partial maps of the fruit fly genome:

In the 1930's Miller and Timofeeff found that the frequency with which a specific mutation (of fruit flies) occurred varied linearly with the total X-ray exposure of the system. Max Delbruck was able to deduce from this that genes are single molecules.

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