Q.1 Under alkaline conditions, DNA is more stable than RNA because
(A) RNA forms secondary structures
(B) RNA is a single stranded molecule
(C)RNA has uracil in place of thymidine
(D)RNA is susceptible to hydrolysis
Why DNA Outshines RNA in Alkaline Stability
DNA demonstrates superior stability over RNA under alkaline conditions due to RNA’s inherent vulnerability to base-catalyzed hydrolysis. This multiple-choice question highlights a core principle in molecular biology, pivotal for biotech students and researchers.
Correct Answer
The right choice is (D) RNA is susceptible to hydrolysis. RNA’s 2′-OH group on ribose enables nucleophilic attack on the phosphodiester backbone in high pH, cleaving it via a 2′,3′-cyclic phosphate intermediate. DNA lacks this group, rendering it resistant.
Option Breakdown
(A) RNA Forms Secondary Structures
Secondary structures like hairpins stabilize RNA against nucleases but do not explain alkaline instability. Under alkali, hydrolysis targets the backbone directly, bypassing structure.
(B) RNA Is Single-Stranded
Single-strandedness exposes RNA to enzymes, yet alkaline degradation is chemical, not enzymatic. DNA’s double helix offers protection, but the key difference remains the sugar.
(C) RNA Has Uracil Instead of Thymidine
Uracil vs. thymine affects repair (thymine’s methyl aids mismatch detection), not hydrolysis. Base choice plays minimal role in alkaline conditions.
Alkaline Hydrolysis Mechanism
In alkali, OH⁻ deprotonates RNA’s 2′-OH, forming a 2′-O⁻ nucleophile that attacks phosphorus, yielding a cyclic intermediate and strand break. DNA’s 2′-H prevents this, ensuring genome integrity.
