Double-stranded DNA is a cylinder that is 20A wide and 3.4A long per base pair.

Question

Double-stranded DNA is a cylinder that is 20A wide and 3.4A long per base pair. E. coli
chromosome is a single double-stranded molecule that is 4.6 million bp long. An average E. coli cell is a cylinder that is 2 µm long and 1 µm in diameter (1 µm = 10,000 A). Given that the volume of a cylinder is p r2 h, where r = radius of the cylinder and h = height of the cylinder. Calculate how much of the volume of an average E. coli cell is taken up by its chromosome.

( i need step by step explanation, thanks)

Explanation / Answer

Given that

E.coli celll has

height = 2 um = 2 x 10^4 A

diameter = 1 um = 1 x 10^4 A

radius = 0.5 x 10^4 A

Therefore volume = p x r2 x h

                           = 3.14 x 0.5 x 10^4 x 0.5 x 10^4 x 2 x 10^4

                           = 1.57 x 10^12 A

                           = 15000 x 10^8 A

For chromosome,

length is 4.6 x 10^6 base pairs X 3.4 A

diameter = 20 A

radius = 10A

Volume = p x r2 x h

            = 3.14 x 10 x 10 x 4.6 x 10^6 x 3.4

           = 47.6 x 10^8 A

Therefore the 47.6 x 10^8 A is the volume taken up by the chromosome in the E.coli cell of 15000 x 10^8 A.

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