Proteins ppt

• Proteins


  Polymers of amino acids, they’re very large molecules
• Peptide bond


  Bond between amino acids (formed by a condensation reaction where a water molecule is removed)
• Polypeptide


  Chain of amino acids bonded together
• Protein


  Polypeptide that folds & twists into a protein, it is held in place by different types of bonds to form the final protein structure
• Functions of proteins


  • Enzymes
  • Antibodies
  • Carrier proteins (on c.s.m)
  • Receptor proteins (on c.s.m) for hormones /neurotransmitters
  • Transport other molecules in blood e.g haemoglobin
  • Structural proteins – collagen, keratin, muscle fibre proteins
• Amino acid


  Has the same basic structure, the only difference between each one is the R side chain
• There are 20 different R side chains = 20 different amino acids that are joined together in different sequences to form all the different types of polypeptide found in cells
• Each specific polypeptide is made up of different sequences of amino acids - it may not contain all 20 different amino acids - some amino acids will be present many times
• Bonding amino acids together

  Type of reaction- condensation Name of bond = Peptide
• Primary structure


  The sequence of amino acids in a polypeptide chain
• Secondary structure


  The polypeptide chain twists or folds into an alpha-helix or beta-pleated sheet (or both), held in place by hydrogen bonds between the -C=O & -N-H groups of the peptide bonds
• Tertiary structure


  The polypeptide twists & folds even more into the final tertiary shape (for most proteins this is the last level of structure) These are held together by more hydrogen bonds, ionic bonds, disulfide bonds. These bonds form between the groups on the R side chains of the amino acids
• The correct order of amino acids is essential, the R groups must be in the correct place to form —> ionic/disulfide/hydrogen bonds in the correct place to form the correct tertiary structure
• Quaternary structure


  More than one polypeptide chain is bonded together, e.g. Haemoglobin is 4 polypeptides bonded together, Antibodies are also quaternary proteins
• To test for protein, add Biuret A then Biuret B solutions - if a protein is present a purple colour develops
• To extract soluble proteins from food - crush/grind the food in water, filter & collect the filtrate, perform the Biuret test on the filtrate
• Protein denaturation


  If the bonds stabilising the tertiary structure are broken, the protein denatures - hydrogen bonds break if temperature rises too high, ionic bonds break if pH changes too much, disulfide bonds don't usually break, peptide bonds do not break during denaturation
• If too many bonds break the protein will not be able to regain its tertiary structure
• The precise structure of the polypeptide allows the protein to perform its correct function
• Structure of amino acids

  
• Condensation reaction

  
• Atoms involved

  
• Hydrolysis of peptide bond - addition of water molecule- opposite of condensation reaction