Question

If one strand of DNA has the sequence ATGCTTGA, the sequence in the complementary strand would be:
A. TCCGAACT
B. TACGTAGT
C. TACGAATC
D. TACGAACT

Answer 1

Strands of DNA are complementary or we can say that they are anti-parallel to each other. The complementary of T is A and G is C and vice versa.

Complete step-by-step answer: In living cells, certain organic compounds are found such as carbohydrate, lipids, proteins and nucleic acids. The nucleic acids are the polymer of nucleotides. A nucleotide is made up of a pentose sugar molecule, nitrogenous base and phosphate group. In DNA or deoxyribonucleic acid, sugar present is deoxyribose sugar and in RNA or ribonucleic acid, sugar present is ribose sugar. There are 2 types of nitrogenous bases namely purine (adenine, guanine) and pyrimidine (cytosine, uracil & thymine). Adenine, guanine, cytosine are common in both DNA & RNA, thymine is found only in DNA and uracil is found only in RNA. Phosphodiester bond links two nucleosides in the chain of nucleic acid. According to the double helix model given by Watson & Crick to explain DNA structure, DNA is composed of two polynucleotide chains. Both these chains are complementary with each other which mean nitrogenous bases of one polynucleotide chain forms a bond (hydrogen bond) with complementary nitrogenous bases of another chain. Adenine binds with thymine by making two hydrogen bonds and cytosine binds with guanine by making three hydrogen bonds. So if a sequence of one chain of DNA is procured, we can easily suggest the sequence of another chain due to complementary base pairing. Both the chains are also anti-parallel to each other. On the other hand RNA is single stranded or has only one polynucleotide chain.
According to our question, if a sequence of DNA in one strand is ATGCTTGA, then we can suggest a sequence of other strands because of complementary base pairing. The sequence of other strands will be TACGAACT.

Thus the correct option is D.

Note: In double stranded DNA the amount of purine nucleotides is equal to amount of pyrimidine nucleotides. If a normal DNA is placed at high temperature then both strands will separate from each other known as denaturation of DNA. Denaturation sometimes makes the protein more active.