A short length of DNA molecule has 80 thymine and 80 guanine bases. The total number of nucleotids in the DNA fragment is
A
160
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B
40
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C
80
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D
320
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E
640
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Solution
The correct option is C 320
According to Chargaff’s rule, in all cellular DNAs, regardless of the species, number of adenosine residues is equal to number of thymidine residues which means that A=T; and the number of guanosine residues is equal to the number of cytidine residues (G= C). Hence, that the sum of the purine residues equals the sum of the pyrimidine residues, i.e., A + G = T + C.
Hence, a DNA strand with 80 thymine and 80 guanine bases will have 80 adenine and 80 cytosine bases. This makes total 80+80+80+80 = 320 bases and therefore, 320 nucleotides in that DNA molecule.