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Genes

Biology: AQA A Level, topic 4.1.2

Genes

DNA consists of millions of genes. Genes are a section of DNA that code for a polypeptide or RNA molecule.

Base sequence

Base sequence

  • DNA is made from four different bases (A, T, C, G).
  • A gene is a sequence of bases in DNA.
  • Each gene has a specific base sequence.
Locus

Locus

  • The specific location of a gene in the DNA is called the locus.
  • The locus is a fixed position.
Codons

Codons

  • Three bases in a gene are called a triplet or a codon.
  • A specific codon encodes a specific amino acid.
  • The codons present in a gene and the sequence of the codons are translated into a sequence of amino acids.
  • Together these amino acids form a polypeptide.
mRNA

mRNA

  • The sequence of bases in a gene is made into a polypeptide by copying DNA into a molecule called messenger RNA (mRNA).
  • mRNA is then copied into the corresponding polypeptide.
Functional RNA molecules

Functional RNA molecules

  • Some genes encode a functional RNA molecule instead of a polypeptide.
  • Functional RNA molecules are necessary for protein synthesis.
  • E.g. Transfer RNA (tRNA) helps find the correct amino acids for a specific codon.
  • E.g. Ribosomal RNA (rRNA) are a part of ribosomes, the centre of protein synthesis.

Test yourself on Genes

  • Which RNA molecule copies the DNA sequence into a polypeptide?

  • Which of the following statements about genes are true?

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