Biology · Molecular Basis of Inheritance · NEET
| Sugar | Deoxyribose (2'-deoxyribose, -H at 2') | Ribose (extra -OH at 2') |
| Pyrimidine base | Thymine (with cytosine) | Uracil (with cytosine) |
| Strands | Usually double-stranded (double helix) | Usually single-stranded |
| Stability | More stable (no 2'-OH; thymine) | Less stable (reactive 2'-OH; uracil) |
| Main role | Long-term storage of genetic information | Protein synthesis (mRNA, tRNA, rRNA); catalysis |
The three key differences NEET tests are: (1) Sugar - DNA has deoxyribose, RNA has ribose. (2) Base - DNA has thymine, RNA has uracil (both share adenine, guanine and cytosine). (3) Strands - DNA is usually double-stranded, RNA is usually single-stranded. NCERT (Ch 5, p.80) says the nucleotide has a pentose sugar 'ribose in case of RNA, and deoxyribose for DNA'.
RNA has ribose and DNA has 2'-deoxyribose. The difference is at the 2' carbon: ribose has an -OH group there, while deoxyribose has only -H (one oxygen less, so 'deoxy'). NCERT: 'In RNA, every nucleotide residue has an additional -OH group present at 2'-position in the ribose.' Arabinose is NOT the sugar of either - NEET uses arabinose as a wrong option to trick you.
RNA has uracil, not thymine. DNA has thymine. Cytosine is common to both. NCERT states: 'in RNA the uracil is found at the place of thymine (5-methyl uracil, another chemical name for thymine).' So thymine is basically a methylated uracil. Remember: Thymine = DNA, Uracil = RNA.
DNA is usually double-stranded (two chains coiled into a double helix, held by hydrogen bonds between base pairs A=T and G=C). RNA is usually single-stranded. Note the word 'usually' - some viruses have single-stranded DNA or double-stranded RNA, but for standard NEET answers use DNA = double, RNA = single.
DNA is chemically more stable because it lacks the reactive 2'-OH group that RNA has on its ribose. That extra -OH makes RNA easier to break down (hydrolyse). Also, thymine (in DNA) is more stable than uracil (in RNA). This stability is why DNA, not RNA, is the preferred genetic material for long-term storage of information - an important point in the 'properties of genetic material' topic.
Both are nucleic acids made of nucleotides; each nucleotide has a nitrogenous base, a pentose sugar and a phosphate group joined by phosphodiester bonds. Both share the purines adenine and guanine, and the pyrimidine cytosine. Both carry genetic information (DNA in most organisms, RNA in some viruses).
The correct statement regarding RNA and DNA, respectively is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Adenine, guanine and cytosine are found in both. Thymine is only in DNA and uracil is only in RNA.
Uracil is a pyrimidine, just like thymine and cytosine. The purines are adenine and guanine (present in both DNA and RNA).
Yes. In some viruses (like the tobacco mosaic virus and influenza), RNA is the genetic material. But in most organisms DNA is the genetic material because it is more stable.
It means one oxygen is missing at the 2' carbon of the sugar. Ribose has an -OH group there; deoxyribose has only -H. This single change makes DNA more stable than RNA.
