USA Biology Olympiad (USABO) Practice Exam

What is the primary structural component of RNA that contributes to its instability?

1. Ribose sugar

2. Phosphate backbone

3. Double-stranded structure

4. Uracil bases

The correct answer is: Ribose sugar

The primary structural component of RNA that contributes to its instability is the ribose sugar. RNA contains ribose, which has a hydroxyl (-OH) group attached to the 2' carbon atom. This hydroxyl group makes RNA more reactive and susceptible to hydrolysis compared to DNA, which has deoxyribose that lacks the 2' hydroxyl group. The presence of the hydroxyl group in ribose can lead to cleavage of the RNA strand under certain conditions, thus contributing to its overall instability. In contrast, the other components mentioned, such as the phosphate backbone, are generally stable and do not contribute to instability. The double-stranded structure is characteristic of DNA rather than RNA, where RNA typically exists as a single strand. Lastly, uracil bases, which replace thymine in RNA, do not specifically contribute to instability; their role is mainly in base pairing and protein synthesis rather than affecting the structural integrity of the RNA molecule.