Protein Synthesis (SQA National 5 Biology): Revision Note

Protein synthesis

• Protein synthesis is the process by which proteins are built within cells

• This process of protein synthesis occurs in two stages:

  • a messenger RNA (mRNA) copy of the genetic code is produced

  • the protein is assembled at a ribosome

Producing an mRNA copy

• The first stage of protein synthesis occurs in the nucleus; an mRNA copy of the genetic code is produced as follows:

  1. part of a DNA molecule unwinds when the bonds between the base pairs break

  2. the gene from which a particular protein will be produced is exposed

  3. an enzyme makes a complementary copy of the DNA from the gene by building a single-stranded molecule known as mRNA

• The mRNA molecule leaves the nucleus

Assembling a protein

• After leaving the nucleus the mRNA molecule attaches to a ribosome in the cytoplasm; a protein is then assembled as follows:

  • the mRNA passes through the ribosome

  • each triplet of bases in the mRNA molecule codes for a specific amino acid

  • the ribosome converts the sequence of bases into a sequence of amino acids that make up a protein