Question

DNA differs from RNA in

A. Nature of sugar alone
B. Nature of purines alone
C. Nature of sugar and pyrimidines
D. None of the above

Answer 1

Hint: Full form of DNA is deoxyribonucleic acid and RNA is ribonucleic acid. The naming is based on type of sugar. RNA has uracil and no Thymine and vice versa for DNA. Uracil, Cytosine and Thymine are pyrimidine bases.

Complete answer:
1.Nucleic acids are building blocks of our hereditary material. There are two types of nucleic acids, DNA and RNA.
2.Nucleic acids are polymers made of nucleotides. Nucleotides are monomeric units each comprising a sugar (deoxyribose for DNA, ribose for RNA), attached to a phosphate group and a nitrogen base.
3.The ribose sugar has a hydroxyl group (-OH) in the 2’position of the ring and deoxyribose is devoid of the extra oxygen at this position and has only an hydrogen atom.
4.Nitrogen bases of nucleotides are of two types depending on the type of aromatic rings. These are purines or pyrimidines.
5.Purines have heterocyclic rings. There are two purine bases: Adenosine and Guanosine. 6.Both Adenosine and Guanosine are present in DNA as well as RNA. When conjugated with respective sugar residues these are known as Adenine and Guanine nucleotides.
7.Three different types of pyrimidines are found in nucleic acids : Thymine, Uracil, and Cytosine. Cytosine is common to both DNA and RNA, but Uracil is found in RNA alone and Thymine is restricted to DNA only.

Hence the correct answer is OPTION(C)

Note: Of the three possible pyrimidines only, cytosine is common to both. Cytosine always complements Guanosine.
Thymine complements Adenine in DNA and Uracil complements adenine in RNA.