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joebob joebob
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9 years ago
The double-stranded DNA molecule of a newly discovered virus was found by electron microscopy to have a length of 102 micrometers (102 x 10^4 A).

(a) How many nucleotide pairs are present in one of these molecules?

(b) In the duplex DNA of the virus, how many complete turns of the double helix are present?
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wrote...
9 years ago
68 micrometers = 680,000 angstroms

Number of base pairs = (680,000/3.4) = 200,000 number of base pairs

As there are 10 base pairs per turn, there should be 2 million complete turns in such a molecule.
wrote...
9 years ago
The DNA double helix contains exactly 10 nucleotide pairs per turn and each nucleotide pair occupies 3.4 angstroms. So one unit will be:

3.4*10= 34 Angstroms long

Now your answers:

a.

Since 34 Angstroms of 1 unit has 10 nucleotide pairs

for 680000 Angstroms, there will be 680000/34=20000 units available

and therefore Number of nucleotide= 20000*10= 200000 nucleotide pairs.



b.

each unit represents one turn, so there will be 20000 complete turns.
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