Proteins

• Proteins are a diverse group of large and complex polymer molecules, made up of long chain of amino acids
• biological roles of proteins


  • structural- main component of skin, muscle, ligaments and hair
  • catalytic- all enzymes are proteins, catalyzing many biochemical reaction
  • signalling- many hormones and receptors are proteins
  • immunological- all antibodies are proteins
• Structure of amino acids: all amino acids have the same general structure, the only difference between each one is the nature of the R group. The R group therefore defines an amino acid. The R group represents a side chain from the central 'alpha' carbon atom, and can be anything from a simple hydrogen atom to a more complex ring structure

  A) amino group

  B) R Group

  C) carboxyl group

  
• Peptide bonds and dipeptides

  A) peptide bonds

  B) dipeptide

  C) amino acid

  D) amino acid

  
• polypeptides

  • when more amino acids are added to a dipeptide, a polypeptide chain is formed.
  • a protein consists of one or more polypeptide chains folded into a specific 3d shape.
  • there are up to 4 levels of structure in a protein: primary, secondary, tertiary and quaternary.
• Bonds in protein

  A) hydrogen bonds

  B) hydrophobic interactions

  C) disulfide bonds

  
• what is the test for proteins


  biuret test
• fibrous proteins are formed from parallel polypeptide chains held together by cross-links. these form long, rope-like fibres with high tensile strength and are generally insoluble in water.
• fibrous fibres


  • collagen- the main component of connective tissue such as ligaments, tendons and cartilage
  • keratin- the main component of hard structures such as hair, nails, claws and hooves
  • silk- forms spiders webs and silkworms cocoons
• Globular proteins usually have a spherical shape caused by tightly folded polypeptide chains. the chains are usually folded so that hydrophobic groups are on the inside, while the hydrophilic groups are on the outside. this makes many globular proteins soluble in water
• globular proteins

  • transport proteins- such as haemoglobin. myglobin and those embedded in membranes
  • enzymes- such as lipase and DNA polymerase
  • hormones- such as oestrogen and insulin
• Denaturing proteins


  if the bonds that maintain a proteins shape are broken, the protein will stop working properly and is denatured. changes in temperature, pH or salt concentration can all denature a protein, although the specific conditions will vary from protein to protein. Fibrous proteins lose their structural strength when denatured whereas globular proteins become insoluble and inactive