Question

Purines of DNA are represented by
a) Uracil and thymine
b) Guanine and adenine
c) Uracil and cytosine
d) Thymine and cytosine

Answer 1

Hint: DNA or deoxyribonucleic acid is mainly composed of purines and pyrimidines base pairs. The DNA present is double-stranded and is in a helical structure. The deoxyribose attaches to the nitrogenous base and together they form a nucleoside.

Complete answer:
Purine is a heterocyclic organic aromatic compound. They consist of adenine and guanine. Purines are the weak basic compound. They exist in different tautomeric forms in different ph. surroundings. At neutral ph., purines are hydrophobic and relatively insoluble in nature. The purines are stabilized by the resonance in the ring structure. They have a pyrimidine ring fused with the imidazole ring system.

Additional information: Pyrimidine is a six-membered organic heterocyclic compound. They are also the weak basic. They are also hydrophobic in nature when present in the neutral ph. surrounding. They exist in different tautomeric forms when present in the different ph. They are composed of thymine, cytosine, and uracil. In DNA thymine and cytosine are present whereas, in RNA thymine is replaced by the uracil base pair. Watson and Crick gave the double-helix model of the DNA. The strand so the DNA is complementary or antiparallel to each other. The backbone of the DNA is composed of the sugar-phosphate. Purines base pairs with the pyrimidines and the number of purines present is always equal to the number of pyrimidines. Adenine and thymine bind together with the double bond and the guanine and cytosine bond together by the triple bond.

So, the answer is ‘adenine and guanine’.

Note: The two strands of the DNA are antiparallel in nature. Each strand has a 5’ and a 3’ end at the end of which there is a presence of phosphate group and a hydroxyl group respectively. The shape of the helix is stable due to the presence of hydrogen bonds between the bases.