Q.Which of the following base is not present in DNA ?

DNA contains adenine, guanine, cytosine and thymine as its four bases; uracil is found in RNA (in place of thymine) and does not occur in DNA.

Nucleic acids use two purine bases (adenine, guanine) common to both DNA and RNA, and one pyrimidine base each that differs between the two: DNA uses thymine (5-methyluracil) as its second pyrimidine base (along with cytosine), while RNA uses uracil (lacking the methyl group thymine has) instead of thymine. This structural distinction (thymine in DNA vs. uracil in RNA) is one of the defining chemical differences between the two nucleic aci …