Question

DNA consists of two complementary nucleotide chains. If the sequence of nucleotide in one of the chains is AGCTTCGA, then the nucleotide sequence in the other chain shall be
A. TAGCATAT
B. GATCCTAG
C. TCGAAGCT
D. GCTAAGCT

Answer 1

Hint: DNA is a long chain of deoxyribonucleotides. A nucleotide has a nitrogenous base, a pentose sugar and a phosphate group. The pentose sugar can either be DNA or RNA.

Complete Answer:
DNA (deoxyribo nucleic acid) is made up of two polynucleotide chains. The chains possess antiparallel polarity. There are two kinds of nitrogenous base
1. Purines: Adenine and Guanine
2. Pyrimidines: Cytosine, Uracil and Thymine

The ratio between Adenine and Thymine and Guanine and Cytosine are constant and equal. The base pairs in each nucleotide chain are formed through hydrogen bonds. Adenine forms two hydrogen bonds with Thymine from opposite strands and vice-versa. Guanine forms three hydrogen bonds with Cytosine

 Now, the sequence given in the question is: AGCTTCGA . if we read this sequence from left and from right it appears to be the same. Such a sequence is called palindrome sequence.
As stated above, A forms bond with T and C with G. Thus, the sequence of the other chain should be :

A ⟶ T	G ⟶ C	C ⟶ G	T ⟶ A
T ⟶ A	C ⟶ G	G ⟶ C	A ⟶ T

Hence, the option ‘C’ TCGAAGCT is the correct answer to this question.

Note: A Purine always comes opposite to Pyrimidine. Base pairs are complementary to each other. The two polynucleotide chains are coiled in a right-handed fashion.