Protein Synthesis

Protein Synthesis

  • There are 20 different amino acids in human proteins. A cell uses the sequence of bases in DNA to synthesise chains of these amino acids. These chains form proteins and this process is called protein synthesis.
  • Each amino acid is identified by a different group of bases. A specific order of bases in DNA produces a specific order of amino acids in the chain and therefore produces a particular protein.


  • The first process of making a protein is called transcription. This takes place in the nucleus.
  1. The DNA in a gene unzips by breaking the weak hydrogen bonds holding the bases together in the double helix.
  2. mRNA (messenger) nucleotide in nucleus
  3. mRNA nucleotides bind with complementary bases on the coding strand NB: Thymine becomes Uracil in RNA
  4. mRNA strand leaves nucleus through nuclear pores by detaching from the coding strand
  5. DNA zips up


  1. mRNA attaches to a ribosome in the cytoplasm.
  2. Ribosome decodes the mRNA
  3. tRNA (transfer) codons are attached to amino acids, each codon has a different amino acid
  4. tRNA codons join to the complementary codons (bases) on the mRNA
  5. As more amino acids are brought by the tRNA they bond together with peptide bonds.
  6. Long chain of amino acids forms a polypeptide
  7. Protein formed.