Question

What is the difference between sugar of RNA and DNA?

Hint:

A simple memory trick: "R" in RNA stands for Ribose (with extra \(-OH\)), while "D" in DNA stands for Deoxy (without oxygen at 2'-carbon).

Answer 1

The main difference between RNA and DNA lies in the type of sugar molecule present in their nucleotides. Both nucleic acids contain a five-carbon sugar, but their structures vary slightly, which leads to differences in their properties and biological roles.

Step 1: Sugar in RNA.
In RNA (Ribonucleic Acid), the sugar is called ribose. Ribose is a pentose sugar with the following structural feature: \[ \text{At the 2' carbon atom, ribose has a hydroxyl group (-OH).} \] This hydroxyl group makes RNA chemically more reactive and less stable under alkaline conditions. As a result, RNA molecules are usually single-stranded and perform temporary roles in cells such as protein synthesis (mRNA, tRNA, rRNA).

Step 2: Sugar in DNA.
In DNA (Deoxyribonucleic Acid), the sugar is called deoxyribose. The difference is: \[ \text{At the 2' carbon atom, deoxyribose has only a hydrogen atom (-H) instead of a hydroxyl group.} \] This small change makes DNA chemically more stable, less reactive, and well-suited for long-term storage of genetic information.

Step 3: Functional Implications. \[\begin{array}{rl} \bullet & \text{The presence of the extra \(-OH\) group in ribose makes RNA more prone to hydrolysis, limiting its stability. This is why RNA is usually short-lived and functions as an intermediary in the flow of genetic information.} \\ \bullet & \text{The absence of the \(-OH\) group in deoxyribose provides DNA with higher resistance to enzymatic breakdown and chemical damage. This stability is critical for DNA's role in storing genetic information across generations.} \\ \end{array}\]

Step 4: Summary of Difference. \[ \text{RNA sugar: Ribose → has -OH at 2' carbon.} \] \[ \text{DNA sugar: Deoxyribose → has -H at 2' carbon.} \]