Question

What are the three components that make up a nucleotide? Which of these are responsible for joining the nucleotides together in a chain and which are involved in the association of two nucleotide strands in a double helix?

Answer 1

A nucleotide is made up of three components, namely a nitogen base, a sugar and one or more phosphate groups.

Nitrogen base : A nucleotide should contain any of the four nitrogen bases. These bases include adenine, thymine, guanine and cytosine. In case of RNS, thymine is absent, instead uracil is present. The base are categorized into two-purine and pyrimidine. Purine bases have double ring stucture. Adenine and Guanine are the purines.Pyrimidines have a single ringed structure. Thymine, Cytosine and Uracil comes under this category.

Sugar : A nucleotide will contain a pentose sugar. In case of DNA, it is deoxyribose and in case of RNA it should be ribose.

One or phosphate groups are also be present.

Nucleotides are bound together by the hydrogen bonds formed by the nitrogen bases. Adenine is always bonded to thymine. They form a double bond i.e., A=T. In case of RNA, thymine is replaced by uracil i.e., in RNA it is U=T. Cytosine is always bonded to guanine. They form a triple bond. It is thus clear that a purine base always bonds with a pyramidine only.

The bonding between purines and pyrimidines result in the double helical structure.