Question

In one polynucleotide strand of a DNA molecule, the ratio of A+T/G+C is 0.3. what is the A +G/T +C ratio of the entire DNA molecule?
A. $$0.3$$
B. $$0.6$$
C. $$1.2$$
D. 1

Answer 1

Hint: In one polynucleotide strand of a DNA molecule ratio is given A +T/G +C which is $$0.3$$ and ratio of the entire DNA molecule will be 1 due the Chargaff’s rule. The A stand is for adenine, T is for thymine and G is for guanine and C is for cytosine which are joined through covalent bonds.

Step by step answer:The polynucleotides are the nucleotides which are the building blocks of the polymer, there are five nucleotides known as the Adenine, Thymine, Guanine, Cytosine and Uracil. These are joined together by the covalent bonds, pairing is always done as A-T and G-C. Given ratio of A+T/G+C is species-specific ratio and it is $$0.3$$, whereas, A +G/T +C is the ratio which is constant for all the double-stranded DNA where the value of it is 1, that is because in ds-DNA base adenine will always bind to the cytosine which is G = C and purines will always be equal to pyrimidines according to Chargaff's rule.
Hence, the correct option is ‘D’.

Note: In a DNA molecule ratio of A +T/G +C is different for different species but it is constant for particular species. The ratio A +T/G +C is always constant for all double stranded DNA and the value of it is 1 due to dsDNA, where A is always equal to T and is present in the same number, it is similar in the G and C where the number is also the same.