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Estimating the charge on DNA

Page history last edited by Joe Redish 9 years, 8 months ago

4.2.4.P8a

 

When a DNA molecule is in water, each base pair releases a pair of hydrogen ions. As a result, the DNA molecule has a net charge. Since there are a lot of base pairs in a string of DNA, this can be a lot of charge!

 

On the web, find a reliable site (and say why you think it is reliable) that tells you the number of base pairs in a typical human chromosome. (Not the Y chromosome!) To get a sense of the total amount of charge involved, imagine that you had two coiled up chromosomes, each with a charge of 2 extra electrons per base pair. Suppose you held them fixed in a vacuum one micrometer apart. For simplicity, model the chromosomes as point charges.

 

Estimate the electric force that the two chromosomes exert on each other in this situation. Explain why this kind of electrostatic repulsion is not a problem when DNA is in its natural environment.

 

You may take the Coulomb constant to be kC  ~ 9 x 109 N-m2/C2.

 

 

Redish 3/17/14

 

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