Proteins (general strcuture)

• Peptide chain

  Polypeptides made up of amino acids bonded by peptide bonds
• Amino acids


  • Monomers that form the polymers proteins which are polypeptides
• Formation of polypeptides


  1. Condensation of 2 amino acids forming a peptide bond -> Dipeptides

  2. Condensation of many amino acids joined by peptide bonds-> Polypeptides

  3. Combining the -OH from the carboxyl group of one with -H from the amino group of another makes the water in the condensation reaction
• Structure of amino acids

  • Each amino acid has a central carbon atom (alpha carbon)
  • 4 atoms/ groups of atoms bonded to the central carbon atom: NH₂ (an amine group), COOH (a carboxyl group), H (a hydrogen atom), R (a side group)
• 1. groups

  Different R groups in every amino acid, determines how the amino acid interacts & bonds with other amino acids in the polypeptide
• Glycine

  • Amino acid with a hydrogen atom in its R- group, only amino acid that does not have a carbon atom in its R group
• Amino acids

  • 20 different types common in all organisms (only differ in their R groups)
  • 10= essential amino acids (the human body cannot produce them so are obtained from diet)
• Peptide bond

  Bond formed between the carboxyl group of 1 amino acid and the amine group of a 2nd, one water molecule is released as a by-product
• Polypeptides

  • Made from chains of amino acids, amino acids are at each end of the polypeptide chain= form the two end terminals (the N- terminal: amine terminal & the C- terminal: carboxyl terminal)
• Functions of proteins


  • Transport proteins (including channel proteins)
  • Enzymes
  • Antibodies
  • Structural proteins
• Biuret test


  1. Add sample to distilled water & biuret solution (grind in water if the substance is solid)

  2. Analyse results: Blue -> violet when proteins are present, not if it contains only free amino acids
• Primary structure of proteins

  Order of amino acids in a polypeptide determines the protein's primary structure, determined by the gene encoding the protein
• Change in the nucleotide sequence of the genes coding region

  May lead to a different amino acid being added to a growing polypeptide chain, change in the amino acids in a protein could change the proteins structure & function
• Secondary protein structure


  The primary polypeptide chain fold to form a secondary structure, hydrogen bonds cause the protein to fold into specific structures like alpha helix & beta pleated sheet
• Stability of secondary structure

  • Individual hydrogen bonds are weak but there are many so overall have a high stability, stability decreased by environmental factors that weaken hydrogen bonds (eg temperature and pH)
• Tertiary structure


  The secondary polypeptide folds further to form a tertiary, 3D polypeptide chain, interactions between R-groups create the complex 3D structure
• Interactions holding tertiary structure

  • Ionic bonds, hydrogen bonds, disulphide bridges, when the protein loses its 3D shape it may no longer be functional
• AMINO ACID STRUCTURE: