Question

In DNA the complementary bases are 

(a) adenine and thymine, guanine and cytosine 

(b) uracil and adenine, cytosine and gaunine 

(c) adenine and guanine, thymine and cytosine 

(d) adenine and thymine, guanine and uracil

Answer 1

(a) adenine and thymine, guanine and cytosine 

In DNA, the complementary bases are adenine and guanine ; thymine and cytosine. Each nucleotide in DNA is composed of a nitrogen containing base, either guanine (G), adenine (A), thymine (T), or cytosine (C) as well as a monosaccharide sugar called deoxyribose and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules (A with T and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA.