1. Protonation of the 2'-hydroxyl group: In acidic solutions, the 2ʹ-hydroxyl group of the ribose sugar in RNA becomes protonated, forming a positively charged 2ʹ-oxonium ion.
2. Nucleophilic attack by water: The protonated 2ʹ-oxonium ion makes the RNA backbone susceptible to nucleophilic attack by water molecules. The lone pair of electrons on the oxygen atom of water attacks the phosphorus atom in the phosphodiester bond.
3. Formation of a cyclic intermediate: The nucleophilic attack by water results in the formation of a cyclic intermediate known as a 2ʹ,3ʹ-cyclic phosphate. This cyclic structure is relatively stable due to the presence of positive charge on the phosphorus atom and the negative charge on the oxygen atom.
4. Hydrolysis of the cyclic intermediate: The cyclic intermediate is then hydrolyzed by water molecules, resulting in the breaking of the phosphodiester bond. This leads to the release of a 3ʹ-hydroxyl group on one nucleotide and a 5ʹ-phosphate group on the adjacent nucleotide.
The overall effect of acid hydrolysis on RNA is the cleavage of the phosphodiester bonds between nucleotides, leading to the fragmentation of the RNA molecule into smaller pieces. This process can be accelerated under harsh acidic conditions, such as high concentrations of acid or elevated temperatures.
In contrast, DNA is more resistant to acid hydrolysis because it lacks the 2ʹ-hydroxyl group in its sugar backbone. Instead, DNA has a 2ʹ-deoxyribose sugar, which lacks the hydroxyl group and therefore does not undergo the same acid-catalyzed hydrolysis. This difference in susceptibility to acid hydrolysis is one of the factors that contribute to the greater stability of DNA compared to RNA in biological systems.
