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A structural unit of nucleotide is called nucleotide in a biological system. A nucleotide has three components - a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present RNA at the place of Thymine. A nitrogenous base is linked to the OH of 1'C pentose sugar through a N-glycosidic linkage to form a nucleoside.
(i) What is the key difference between nucleoside and nucleotide ? (a) Nitrogen (b) Phosphate group (c) Pentose sugar (d) Hydrogen bond(ii) Which of the following group is of pyrimidine ? (a) Adenine and Guanine (b) Guanine and Cytosine (c) Cytosine, Thymine and Uracil (d) Adenine and Thymine(iii) Which nitrogen base is present in RNA, instead of thymine ? (a) Guanine (b) Uracil (c) Adenine (d) Cytosine(iv) Where does N-glycosidic bond formed in following ? (a) Between two nitrogen base (b) Between Sugar and phosphate (c) Between nitrogen base and pentose sugar (d) Between amino acid and sugar

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