Question

A sample of DNA is found to have the base composition (mole ratio) of A = Forty, T = Twenty two, G = Twenty one and C = Seventeen. This suggests
A) DNA is circular duplex
B) DNA is linear duplex
C) DNA is single stranded
D) DNA has high melting point

Answer 1

Hint:A base pair is two chemical bases bonded to one another forming the rung of the DNA ladder. The DNA molecule consists of two strands that wind around each other like the twisted ladder.They are attached to each sugar that is one of the four bases adenine, cytosine, guanine, or thymine.

Complete answer:
According to Chargaff's rule, DNA from any cell of all the organisms has pyramiding and purine.
Hence, the amount of the guanine is equal to the cytosine and the amount of adenine is equal to the thymine. This is because, in DNA, the adenine pairs with the thymine and the guanine pairs with the cytosine. But in the given sample of DNA, the mole ratio of the purines and the pyrimidines does not satisfy this rule. Therefore, the given DNA is single stranded.

Additional information:
The circular DNA is the DNA that forms a closed loop and has no ends.For examples this include: Plasmids, mobile genetic elements.The duplex DNA is the other name for double-stranded DNA.
This means that the nucleotides of the two DNA sequences have bonded together and then coiled to form the double helix. The cytosine and the guanine are held together by three hydrogen bonds, where the adenine and the thymine are held together by only two.Increased hydrogen bonding within a strand of DNA will increase the melting point.

Hence the correct answer is option ‘C’.
Note:The Chargaff’s rules state that the DNA from any cell of any organism should have a stoichiometric ratio of the pyrimidine and the purine bases and, more specifically, that the amount of the guanine should be equal to the cytosine and the amount of the adenine should be equal to the thymine.