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GCSE Biology · key term
The variable part of a DNA nucleotide; the four bases are adenine, thymine, cytosine and guanine.
Used by AQA, Edexcel and OCR
Specification 4.6.1.5 · Paper 2
One of the four variable parts of a DNA nucleotide, represented by A, C, G or T.
Revise: DNA Structure and the Genetic CodeEvery nucleotide has the same kind of sugar and a phosphate group, but its attached base can be one of four types: A, C, G or T. These letters name the bases, not four different sugars.
Specification 3.7B · Paper 1
One of the chemical units arranged in sequence along DNA; the order of these bases carries genetic information.
Revise: DNA and ProteinsDNA stores biological information in the order of its bases. A gene is a section of DNA that codes for a particular protein. It is not simply the presence or number of bases that provides the instruction: their sequence matters, just as changing the order of letters can change the meaning of a word.
Specification B1.2c · Paper 1 (Foundation), Paper 3 (Higher)
One of four possible components attached to the sugar in a DNA nucleotide: adenine, thymine, guanine or cytosine. Each nucleotide has one base.
Revise: NucleotidesEach DNA nucleotide has three parts: a sugar, a phosphate group and a base attached to the sugar. The sugar and phosphate group are the same in all four types of DNA nucleotide. Only the base changes.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Revise: NucleotidesThe sugar and phosphate group are common to all four types. It is the base that varies.
When interpreting a DNA diagram, identify the alternating sugar–phosphate backbone and the base attached to each sugar. AQA expects you to interpret such a diagram, not reproduce it.
Keep the two sequences distinct: bases are ordered in DNA; amino acids are ordered in a protein. Three bases code for one amino acid, not one whole protein.
Do not confuse a nucleotide with a base: a nucleotide contains a sugar, a phosphate group and a base.
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