Question

DNA and RNA:

A. One difference between RNA and DNA is the pentose sugar. What characteristics are affected by the type of sugar in the molecule?

B. Why can there be unusual base pairings in RNA, but with DNA it has to be GC and AT base pairs only?

Answer 1

A) DNA contains the deoxyribose sugar, while RNA contains the ribose sugar. Due to its deoxyribose sugar, which contains one less oxygen-containing hydroxyl group, DNA is a more stable molecule than RNA, which is useful for keeping genetic information safe. This structural difference makes DNA more stable under alkaline conditions than RNA. RNA is not stable. The C-H bonds in DNA make it fairly stable. The small grooves in the helix also serve as protection, providing minimal space for enzymes to attach. The O-H bond in the ribose of RNA makes the molecule more reactive. The large grooves in the RNA molecule make it susceptible to enzyme attack.

B) The base pairing in DNA including A-T(Adenine-Thymine) and G-C(Guanine-Cytosine) is different from RNA including A-U(Adenine-Uracil) and G-C(Guanine-Cytosine). In RNA, uracil base pairs with adenine and replaces thymine during DNA transcription. Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA. In addition, uracil has more base pair affinity to adenine, but it can also pair up with other bases including itself. This can cause the mutations in genetic material.