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Differences between DNA and RNA

Molecules (Unity and diversity) · Nucleic acids · note 3 of 7

Spec A1.2.7Download all Nucleic acids notes (PDF)Download all notes (PDF)10 pages

Differences between DNA and RNASpec A1.2.7

In short

DNA and RNA differ in three ways examiners look for. DNA is usually double-stranded, while RNA is single-stranded. DNA contains thymine, while RNA contains uracil in its place. DNA contains the sugar deoxyribose, while RNA contains ribose, which has an extra oxygen as an OH group on carbon 2. Examples of RNA include mRNA, tRNA and rRNA.

Differences between DNA and RNA
FeatureDNARNA
Number of strandsTwo (double helix)One
Nitrogenous basesA, T, G, CA, U, G, C (uracil instead of thymine)
Pentose sugarDeoxyriboseRibose

Ribose and deoxyribose

Both sugars are pentoses with a five-membered ring containing an oxygen atom. The difference is on carbon 2: ribose has an OH group there, while deoxyribose has only H, so it has one oxygen atom fewer ('deoxy' means without oxygen).

Simplified ring sketches of ribose and deoxyribose, each with the ring oxygen at the top, carbons numbered 1 to 5 and CH₂OH on carbon 4; ribose has OH on carbons 1, 2 and 3, while deoxyribose has H on carbon 2, circled and labelled no oxygen here. (opens full size in a new tab)
Ribose has an OH on carbon 2; deoxyribose has only H there, so it has one oxygen fewer.

Examples of nucleic acids

  • DNA: the genetic material, found in chromosomes in the nucleus, and in mitochondria, chloroplasts and the cytoplasm of prokaryotes.
  • Messenger RNA (mRNA): a copy of a gene, carried to ribosomes.
  • Transfer RNA (tRNA): carries amino acids to the ribosome during translation.
  • Ribosomal RNA (rRNA): part of the structure of ribosomes.
Common mistake:

In a compare question, write each difference as a matched pair, such as 'DNA contains deoxyribose but RNA contains ribose'. Stating only one side rarely scores.

Written and checked against the IB Biology HL specification · Updated October 2026

Frequently asked questions

What is the structure of a DNA nucleotide?

A DNA nucleotide has a phosphate group, the pentose sugar deoxyribose and a nitrogenous base, which is adenine, thymine, guanine or cytosine. The phosphate and base are attached to the sugar on opposite sides. Nucleotides link through sugar–phosphate bonding to form a strong covalent backbone with the bases sticking out.

Why is DNA described as antiparallel?

DNA is described as antiparallel because its two strands run in opposite directions. The strands are held together by hydrogen bonds between complementary bases, adenine with thymine and guanine with cytosine. In diagrams, one strand is drawn upside down relative to the other to show this.

What are the main differences between DNA and RNA?

DNA is double-stranded, while RNA is single-stranded. DNA contains the base thymine, while RNA has uracil instead. DNA contains the sugar deoxyribose, while RNA contains ribose, which has an OH group on carbon 2 where deoxyribose has only hydrogen. Examples of RNA are mRNA, tRNA and rRNA.

All 5 questions on Nucleic acids