Assertion: A nucleotide has two components – a nitrogenous base and a pentose sugar.
Reason: A nitrogenous base is linked to the OH of 1' C pentose sugar through a N-glycosidic linkage to form a nucleoside.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Assertion is false but Reason is true.
A nucleoside is a nitrogenous base joined to a pentose sugar. A nucleotide is a nucleoside with a phosphate group added. Nucleotides join to form the polynucleotide chains of DNA and RNA.
Assertion: A nucleotide has two components – a nitrogenous base and a pentose sugar. — False. A nucleotide has three components: a nitrogenous base, a pentose sugar and a phosphate group. A base with a sugar only is a nucleoside.
Reason: A nitrogenous base is linked to the OH of 1' C pentose sugar through a N-glycosidic linkage to form a nucleoside. — True. The base joins carbon 1′ of the sugar by an N-glycosidic linkage, and the product is a nucleoside such as adenosine.
NCERT Extract:
Structure of Polynucleotide Chain – “… Let us recapitulate the chemical structure of a polynucleotide chain (DNA or RNA). A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. … A nitrogenous base is linked to the OH of 1′ C pentose sugar through a N-glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine. When a phosphate group is linked to OH of 5′ C of a nucleoside through phosphoester linkage, a corresponding nucleotide (or deoxynucleotide depending upon the type of sugar present) is formed.”