Question
Compare DNA and RNA under the following heads: sugar, nitrogenous bases, number of strands, stability, location in the cell, and function.
(NEET 2024 — this question or a close variant appeared in multiple NEET and CBSE Class 12 board papers. 2–3 marks guaranteed if you get the table right.)
Solution — Step by Step
DNA has deoxyribose sugar — notice the “deoxy” prefix, meaning one oxygen is missing (at the 2’ carbon). RNA has ribose sugar, which has that extra –OH group at the 2’ position. This single –OH group is the root cause of most other differences between the two molecules.
Both share Adenine, Guanine, and Cytosine. The fourth base is where they split: DNA uses Thymine (T), RNA uses Uracil (U). Thymine has a methyl group that Uracil lacks — this makes Thymine slightly more stable, consistent with DNA’s long-term storage role.
DNA is double-stranded (the Watson-Crick double helix), held together by hydrogen bonds — A=T (2 bonds) and G≡C (3 bonds). RNA is single-stranded, though it can fold back on itself locally (as in tRNA’s cloverleaf structure). The double strand gives DNA far greater stability.
DNA stays in the nucleus (and also in mitochondria and chloroplasts in eukaryotes). RNA moves — mRNA is made in the nucleus and travels to the cytoplasm; rRNA is in ribosomes; tRNA floats in the cytoplasm. In prokaryotes, both are in the cytoplasm since there’s no nuclear membrane.
DNA is the master copy — it stores genetic information permanently. RNA is the working copy — mRNA carries the message, tRNA brings amino acids, rRNA forms the ribosome machinery. DNA replicates itself; RNA is synthesised fresh from DNA as needed (transcription).
The Full Comparison Table
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Unique base | Thymine (T) | Uracil (U) |
| Strands | Double | Single |
| Stability | High (stable) | Low (labile) |
| Location | Nucleus, mitochondria, chloroplast | Nucleus + cytoplasm |
| Function | Genetic information storage | Protein synthesis |
| Self-replication | Yes | No (except retroviruses) |
Why This Works
The 2’–OH group in ribose is the key to everything. This –OH makes RNA chemically reactive — it’s why RNA degrades faster than DNA. The body actually wants mRNA to be unstable: once a protein has been made, the mRNA gets broken down so the cell can control exactly how much protein it produces at any time.
DNA’s stability comes from three places working together: deoxyribose sugar (no 2’–OH), Thymine instead of Uracil (the methyl group resists hydrolysis), and the double helix itself (the complementary strand acts as a backup and the base stacking adds thermodynamic stability).
This is also why DNA is kept safe inside the nucleus — it’s the master blueprint. RNA is made, used, and degraded. DNA persists for the lifetime of the cell.
Alternative Method — The “One Letter” Memory Trick
For NEET MCQs, you need instant recall. Here’s how toppers remember:
DNA → Deoxyribose → Double strand → stable → stores Data permanently.
RNA → Ribose → single strand → Reactive → Runs the show (protein synthesis).
For bases: DNA has Thymine (T for Template/permanent), RNA has Uracil (U for Used and discarded).
When NEET asks “which base is NOT found in DNA?” — the answer is Uracil. “Which base is NOT in RNA?” — Thymine. These two have appeared repeatedly as direct MCQs.
Common Mistake
Students often write “RNA is always single-stranded” and then get confused when tRNA structure comes up. tRNA is single-stranded — but it folds into a cloverleaf because complementary regions within the same strand form hydrogen bonds. The molecule itself is still one polynucleotide chain. Never call tRNA double-stranded. NEET has set traps on exactly this point.
A second common slip: writing that RNA cannot replicate. In normal cells this is true — but RNA viruses (like HIV) use reverse transcriptase to copy their RNA genome. If a NEET question specifically asks about viruses, “RNA cannot replicate” is wrong. For standard DNA–RNA comparison questions, you can say RNA does not self-replicate in the cell.
Bottom line: Get the sugar names right (deoxyribose vs ribose), get Thymine vs Uracil right, and remember that DNA’s double-strand + deoxyribose = stability = long-term storage. That logic chain covers every variant of this question.