Question

DNA and RNA differ by

• A. Sugar and phosphate groups
• B. Number of C-atoms in sugars
• C. Nitrogen bases and phosphate groups
• D. Nitrogen bases and sugars

Answer 1

The correct option is (D) Nitrogen bases and sugars

Introduction to the Basic Structure of DNA and RNA

• DNA and RNA are polynucleotide chains, i.e., polymers made up of repeating units of nucleotides.
• The nucleotides are composed of a pentose sugar, a nitrogenous base attached to the 1’ carbon of the sugar and a phosphate group attached to the 5’ carbon of the sugar.
• Adjacent nucleotides are connected with the help of phosphodiester bonds.

Nitrogen Bases in DNA and RNA

• The nitrogenous bases are of 2 types - purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil).
• Both DNA and RNA consist of adenine and guanine.
• DNA and RNA differ in terms of the pyrimidines that they possess. Both consist of cytosine, but while RNA possesses uracil, DNA possesses thymine (5-methyl uracil) in its place.
• Thus, DNA and RNA differ in terms of their nitrogenous bases.

Sugar in DNA and RNA

• Nucleotides in both DNA and RNA consist of pentose sugar having 5 carbon atoms. However, the pentose sugar present in DNA is deoxyribose, and that in RNA is ribose.
• Therefore, we can say that DNA and RNA differ in terms of the sugars that they possess.

Phosphate

The nucleotides in both DNA and RNA possess a phosphate attached to the 5’ carbon of the pentose sugar. In DNA and RNA, this phosphate group participates in phosphodiester bond formation to attach adjacent nucleotides of the polynucleotide chain. Thus, DNA andRNA do not differ in terms of the phosphate groups present in them.

Final answer: (D) Nitrogen bases and sugars

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