DNA and RNA are both made of nucleotides, so they share the same three parts. They differ in three specific ways: the sugar, one of the bases, and the number of strands.
DNA vs RNA at a glance — same three parts, but three differences: the sugar, one base (T in DNA → U in RNA), and the number of strands. Read across each row.
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- Nucleotide
- The monomer of a nucleic acid — a phosphate group, a pentose sugar and a nitrogenous base joined together.
- Pentose sugar
- A sugar with five carbon atoms; deoxyribose in DNA, ribose in RNA.
- Nitrogenous base
- The information-carrying part of a nucleotide: adenine (A), cytosine (C), guanine (G), and either thymine (T, in DNA) or uracil (U, in RNA).
- Strand
- A single chain of nucleotides. DNA has two strands; RNA has one.
DNA
- Sugar is deoxyribose
- Bases: A, C, G and thymine (T)
- Double-stranded (two strands)
- Stores the genetic information long-term
RNA
- Sugar is ribose
- Bases: A, C, G and uracil (U) instead of T
- Single-stranded (one strand)
- Carries / works with the message to make proteins
The three differences to memorise: 1. Sugar: DNA has deoxyribose, RNA has ribose.
2. One base: DNA uses thymine (T), RNA uses uracil (U) in its place.
3. Strands: DNA is double-stranded, RNA is single-stranded.
The phosphate, and the bases A, C and G, are the same in both.
A memory hook: DNA has Deoxyribose and Double strands. RNA swaps Thymine for Uracil — 'U' is the new letter that only appears in RNA.
Phosphorus — needed for more than just DNA: Each nucleotide's phosphate group contains the element phosphorus, so building DNA and RNA needs a supply of phosphorus.
DNA and RNA are not the only ones: two more biochemicals need phosphorus
- ATP (the cell's energy-carrying molecule)
- Phospholipids (the molecules that build cell membranes)
Why it matters: This is why phosphorus is an essential raw material for life — a plant or cell with too little phosphorus cannot make enough DNA, RNA, ATP or phospholipids.
- Biochemical
- A chemical compound made by, and used inside, living organisms (for example a nucleic acid, ATP or a phospholipid).
- DNA and RNA (nucleic acids)
- Their nucleotides each carry a phosphate group, so building them requires phosphorus.
- ATP
- The molecule cells use to carry and release usable energy. The 'P' stands for phosphate — ATP contains three phosphate groups, so it needs phosphorus.
- Phospholipid
- The main molecule of cell membranes. Its 'head' is a phosphate group, so it too contains phosphorus.
If asked to list phosphorus-containing biochemicals: Any two of these score the marks: DNA, RNA, ATP, or a phospholipid.
A safe pair to remember is ATP and phospholipids (or DNA and ATP) — all of them contain a phosphate group, which is the part that holds the phosphorus.
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The big idea: Ribose and deoxyribose are the same ring with one difference: deoxyribose has one oxygen fewer, at carbon 2′.
The points to remember
- Sketch both sugars as five-sided rings with an oxygen at the top.
- The only difference is at carbon 2′: ribose has OH, deoxyribose has just H.
- In a diagram, two strands, thymine or A–T and C–G pairs mean DNA; one strand with uracil means RNA.
- DNA molecules are usually much longer than RNA molecules.
Remember it as: Deoxy- means one oxygen missing.
DNA and RNA are found all over the living world:
DNA
- The genetic material in every chromosome.
- Also in mitochondria and chloroplasts, as small loops.
RNA in every cell
- mRNA (messenger RNA): a copy of one gene.
- tRNA (transfer RNA): brings amino acids.
- rRNA (ribosomal RNA): part of every ribosome.
RNA in viruses
- The genetic material of some viruses.
- Influenza and SARS-CoV-2 carry RNA.
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How it is asked: Distinguish (two contrasts, two marks) and Compare and contrast (similarities and differences). Every difference needs both halves: what DNA has, whereas what RNA has.
A virus that causes the common cold carries RNA, and the human cells it infects carry DNA. Distinguish between the structures of RNA and DNA.
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See the answer broken into clear points, with guidance on how each point earns marks.
And the three-mark version, which also wants what they share:
Compare and contrast the structure of DNA and RNA.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.