Question

If the base sequence of one strand of DNA is CATTAGTAGGAC, what will be the base sequence of complementary DNA strands?

Answer 1

Hint: Base pairing was given based on the observation of Erwin Chargaff which states that the ratio between Adenine and Thymine and Guanine and Cytosine is constant and equal to one. The bases are said to be complementary due to which the sequence of one is complementary to the other. One must infer the salient feature of double- helix structure of DNA.

Complete answer:
DNA is a polynucleotide. A nucleotide has three components- a nitrogenous base, a pentose sugar. There are two types of nitrogenous bases- Purine which includes Adenine and Guanine and Pyrimidines that includes Cytosine, Uracil and Thymine. Cytosine is present in both the DNA as well as in RNA but when we talk about Thymine it is only present in DNA. Uracil is generally present in RNA at the place of Thymine. A nitrogenous base is linked to the pentose sugar through N- glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine.

The purines and pyrimidine are complementary to each other. The base pairs are formed through the hydrogen bonds that are present on the two strands of the base. Adenine is joined with the thymine with the help of the hydrogen bond from the opposite strand and vice- versa. Similarly, when we talk about guanine, it is bonded with the cytosine with the three H- bonds. A is complementary to T amd G is complementary to C and vice versa.

Let us discuss the nucleotide sequence given in the question.
BASE STRAND - CATTAGTAGGAC

The complementary strand of the above sequence is GTAATCATGCTG.

Note: Base pairing confers a very unique property of the polynucleotide chain. In DNA, if each strand acts as a template for the synthesis of a new strand, the two double stranded DNA is formed. The double strand thus formed is generally identical to the parental DNA molecules. It is due to this that the genetic implications of the structure of the DNA are clear.