The main reason RNA is unstable is due to the presence of a hydroxyl (OH) group on the 2' carbon of its ribose sugar.
The 2' Hydroxyl Group's Role in RNA Instability
Unlike DNA, which has a deoxyribose sugar (lacking the 2' OH group), RNA's ribose sugar makes it more susceptible to degradation. This 2' OH group can participate in a nucleophilic attack on the adjacent phosphodiester bond.
- Nucleophilic Attack: The 2' OH group can act as a nucleophile, attacking the phosphorus atom in the phosphodiester backbone of the RNA molecule.
- Self-Hydrolysis: This attack leads to the breaking of the phosphodiester bond, causing the RNA molecule to cleave itself through a process called self-hydrolysis.
- Alkaline Conditions: This hydrolysis reaction is accelerated under alkaline conditions.
DNA vs. RNA Stability
The absence of the 2' OH group in DNA contributes significantly to its greater stability compared to RNA. DNA's deoxyribose sugar makes it much less prone to nucleophilic attack and self-hydrolysis, allowing it to serve as a more durable repository of genetic information.
Summary
In essence, RNA's inherent instability stems from the chemical reactivity of the 2' hydroxyl group on its ribose sugar, leading to increased susceptibility to hydrolysis and degradation.
