Question

Which of the following is a structural subunit of DNA?
a) Proteins
b) Carbohydrates
c) RNA
d) Nucleotides

Answer 1

Hint:-Deoxyribonucleic Acid, abbreviated as DNA, is composed of two strands oriented in the opposite direction. Each DNA chain is composed of repeating subunits comprising nitrogenous bases, a sugar and a phosphate group.

Complete Answer:-
Option (a) is incorrect. Proteins are one of the essential nutrients required by our body. They are composed of amino acids linked by peptide bonds. Proteins are known as building blocks of the body as well a source of energy. It is the most abundant molecule in the body after water and is present in each and every cell of the body. Chief sources of proteins are meat, milk, fish, eggs and legumes.
Option (b) is incorrect. Carbohydrates are compounds containing carbon, hydrogen and oxygen. The most common members of this group are cellulose, sugars and starch. Carbohydrates can be classified into monosaccharide, disaccharide, polysaccharide and oligosaccharide. They function as a storage of energy, in blood clotting, development and fertilization.
Option (c) is incorrect. RNA or Ribonucleic Acid is a nucleic acid comprising a ribose sugar, nitrogenous bases and a phosphate group. In contrast to DNA, RNA is a single stranded molecule. There are different types of RNA like mRNA that conveys genetic information and takes part in protein synthesis, tRNA responsible for transfer of amino acids to ribosomes, rRNA that links amino acids with peptide bonds.
Option (d) is correct. Nucleotides are composed of three parts: a nitrogenous base, a phosphate group and a sugar. The nitrogenous bases are of two types: purines and pyrimidines. The sugar is a ribose sugar or a deoxyribose sugar. Nucleotides are monomeric subunits that form DNA.
Thus, the right option is D.

Note:- Nucleotides are repeating monomers that constitute DNA. Nucleotides typically comprise a nitrogenous base, a phosphate group and a sugar. DNA is a biomolecule present in all cells. A DNA molecule contains two antiparallel strands. It stores biological information and influences all processes like reproduction, growth, metabolism, etc.