Question

Explain the basis of complementary base paring. Given the nucleotide sequence of a single strand of DNA (below), write the sequence of the complementary strand indicating the appropriate 5' and 3 " ends.

Answer 1

DNA double helix structure consists of the polynucleotide chain. This chain has phosphate ion, deoxyribose sugar, and a nitrogenous base. The nitrogenous base sequence forms the genetic language and it is of 2 types in case of DNA i.e. purines and pyrimidines. Purines further consist of adenine(A) and guanine(G) and pyrimidines consist of cytosine(C) and thymine(T) (In RNA, thymine is replaced by uracil, U).

Purines have two rings i.e. pyrimidine ring and imidazole ring. pyrimidines have one ring i.e., pyrimidine ring. Thus, to maintain a uniform distance between the two strands of the DNA (to provide the structural stability), pyrimidines bases pair with purines and vice-versa in case of DNA and in case of double-stranded RNA too.

A binds to Tor U with two hydrogen bonds.

While G binds to C with three hydrogen bonds.

The allowed base pairing are:

Adenine to thymine and vice -versa

cytosine to guanine and vice- versa

In the case of RNA, adenine and uracil and vice-versa pairing is also found.

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