Proteins

• Proteins


  Large polymers made of long chains of amino acids, involved with nearly all cellular functions
• Cells in the body are 50% protein
• Proteins


  • They are extremely important for growth and repair of tissues
  • All proteins have a specific job
• Amino acids


  Monomers of proteins
• Amino acids are made from carbon, oxygen, hydrogen and nitrogen; many also contain phosphorus and sulphur
• Amino acids


  • 21 different types used by humans
• Amino acid structure


  • Central carbon atom
  • Amine group (-NH2)
  • Carboxyl group (-COOH)
  • Hydrogen atom
  • Variable side chains (R groups)
• Carboxyl group


  Carbon atom double bonded to an oxygen atom and single bonded to a hydroxyl (OH) group
• Amino group


  The -NH2 group present in an amino acid
• Protein structural levels


  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure
• Primary structure


  Specific sequence of amino acids forming a polypeptide chain
• Peptide bond formation


  1. Condensation reaction between carboxyl group of one amino acid and amino group of another

  2. Covalent bond formed, water molecule produced
• Polypeptide


  Polymer consisting of a large number of amino acids bonded in a chain
• Covalent bond


  Chemical bond formed when two atoms share one or more pairs of electrons
• Peptide bond


  Covalent bond formed between two amino acids
• Alpha helix (α-helix)


  Right-handed coiled formation in the secondary structure of a protein
• Beta pleated sheet (β-sheet)


  Folding of the primary structure into parallel polypeptide chains
• Tertiary structure


  Coiling and folding of the secondary structure into a 3D shape
• Bonds and interactions in tertiary structure

  • Disulphide bridges
  • Ionic bonds
  • Hydrogen bonds
  • Hydrophobic and hydrophilic interactions
  • Van der Waals forces
• Disulphide bridge


  Covalent bond between two sulphur atoms in R groups
• Ionic bond


  Bond between oppositely charged R groups
• Hydrophilic


  Associates with water molecules easily
• Hydrophobic


  Does not mix with water
• Quaternary structure


  Protein made from more than one polypeptide chain
• Prosthetic group


  Non-protein part of a protein structure that is essential for its function
• Protein with quaternary structure and prosthetic group


  • Haemoglobin
• Globular proteins


  • Soluble, consist of multiple globular sub-units, often contain prosthetic groups
• Globular protein


  • Haemoglobin
• Fibrous proteins


  • Insoluble, consist of protein strands coiled in alpha helices, have structural functions
• Fibrous protein


  • Collagen
• Collagen


  Made up of three polypeptide chains wound around each other in alpha helices, very strong due to hydrogen bonding