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  • Proteins
    • Function
      • Structural components, e.g. of muscle and bone
      • Membrane carriers and pores for active transport and facilitated diffusion
      • All enzymes are proteins
      • Many hormones are proteins
      • Antibodies are proteins
    • Amino acids
      • Proteins are long chains of amino acids - monomers joined together by covalent bonds to form polymers
      • Contain an amino group (NH2), a carboxyl group (COOH), and an R group
      • A condensation reaction occurs between the amino group of one amino acid and the carboxyl group of another
        • A covalent bond is formed between the amino acids and a water molecule is also produced
        • The new bond is a peptide bond and the new molecule is called a dipeptide
      • Peptide bonds can be broken through a hydrolysis reaction, which uses a water molecule
    • Structure
      • Primary
        • The sequence of amino acids found in a protein molecule
      • Secondary
        • When the polypeptides coil to make an alpha helix, or fold to make a beta pleated sheet
        • Hydrogen bonds hold the coils in place. Although they are quite weak, altogether they provide a strong structure
      • Tertiary
        • When the structure coils or folds itself even more, held in place by a number of different types of bonds
        • An increase in temperature will denature the enzymes and break some of the bonds - the whole tertiary structure will unravel and the protein will no longer function properly
      • Quaternary
        • Where a protein consists of more than one polypeptide chain
        • Examples: haemoglobin and collagen
    • Globular
      • Spherical molecules
      • Soluble in water
      • Have metabolic roles
      • Examples: enzymes, plasma proteins, antibodies
    • Fibrous
      • Form fibres
      • Insoluble in water
      • Possess structural roles
      • Examples: collagen, keratin
    • Haemoglobin
      • Quaternary structure with 4 polypeptide sub-units (2 alpha chains and 2 beta chains)
      • Function: carry oxygen from the lungs to the tissues
        • Has 4 haem groups, each with an iron ion - can bind up to 4 oxygen molecules
    • Collagen
      • Made of 3 polypeptide chains wound around each other with hydrogen bonds in between - provide strength
      • Form covalent bonds with other collagen molecules to form fibrils and fibres
      • Provides mechanical strength in many areas of the body, e.g. arteries, skeletal muscle, bones, cartilage


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