Q21 of 30 Page 1

The base sequence in one of the strands of DNA is TAGCATGAT.

(i) Give the base sequence of its complementary strand.


(ii) How are these base pairs held together in a DNA molecule?


(iii) Explain the base complementarity rules. Name the scientist who framed this rule.


i) The base sequence for its complementary strand is ‘ATCGTACTA’.

ii) These base pairs are held together by hydrogen bonds. Between A and T 2 hydrogen bonds are present and between G and C 3 hydrogen bonds are present.


iii) Base complementary Rules were proposed by Chargaff. It states that bond pairs are always formed between A (Adenine) , T (Thymine) and between C (Cytosine) , G (Guanine) i.e. a purine always pairs with a pyrimidine and vice versa.


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