Biology 2.5 Proteins

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Proteins = v. large molecules.

each organism has numerous proteins - differ from species to species.

Most important molecules to life.

Structure of an amino acid

Amino acids = basic monomer units, comine to make polypeptides, which combine to form proteins.

100 amino acids identified, 20 of which naturally occur in proteins.

Every amino acid has central carbon atom attached to 4 different chemical groups:

  • Amino group (-NH2) = basic group, gives amino part of name.
  • Carboxyl group (-COOH) = acidic, gives acid part of name.
  • Hydrogen atom (-H)
  • R group = variety of different chemical groups, different in each amino acid.

Formation of a peptide bond

Amino acid monomers combine to form dipeptide - formed by condensation reaction (removal of a water molecule).

Water molecule = OH from carboxyl group of one amino acid and H of amino group from the other.

2 amino acids then linked by a peptide bond between carbon atom of one and nitrogen atom of the other.

Peptide bonds can be broken down by hydrolysis (addition of water molecule) similar to glycosidic bonds in carbohydrates.

Primary structure of proteins

  • Polymerisation = series of condensation reactions joining together many amino acid monomers, makes a polypeptide.
  • Sequence of amino acids in polypeptide = primary structure of protein.
  • Almost limitless number of possible combinations and


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