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    • amino acids are the monomers for proteins
    • general structure
      variable group R
    • NH2 AMINE GROUP
      COOH CARBOXYL GROUP
      R GROUP SIDE GROUP
    • a condensation reaction between two amino acids forms a peptide bond
    • dipeptides formed by condensation of 2 amino acids
    • polypeptides are formed through the condensation of many amino acids
    • a functional protein may contain one or more polypeptides (these are proteins with a job)
    • the r group is different for every amino acid
    • the r group is different for every amino acid
    • Dna coding determines the sequence of amino acids
    • a peptide bond is formed using the OH part of the carboxyl group of one amino acids and the H part of the amine group in the second amino acid
    • protein is a polypeptide that folds into a 3D shape
      polypeptides don’t have a function UNTIL they are folded
    • four levels of structure in a protein
      • primary
      • secondary
      • tertiary
      • quaternary
    • a polypeptide chain does not become a protein until it folds up into a distinct 3D shape and becomes functional
    • PRIMARY STRUCTURE:
      • this is the unique sequence of amino acids
    • primary structure
      this is the unique sequence of amino acids
      peptide bonds are found between the amino acids,
      there is a carboxyl group at one end and an amine group at the other
    • Secondary structure
      • the way in which the polypeptide bond is either coiled into an ALPHA HELIX or folded into a BETA PLEATED SHEET
      • hydrogen bonds form between the amino acids and hold the structure in place
    • TERTIARY
      • determines the function of the protein, eg active sites in enzymes
      • bonds occur between the R groups on the individual amino acids and cause the alpha helix/ beta pleated sheet to FOLD
      • the folds are held together by ionic bonds, hydrogen bonds and disulphide bridges (covalent bonds between sulphur atoms found on R groups of amino acids)
    • QUATERNARY
      • proteins that contain more than one polypeptide chain
      • eg collagen, haemoglobin
    • a peptide bonds forms between two amino acids during a condensation reaction
    • to test for proteins
      • add sample to biurets solution
      • turns purple for positive
      • blue for negative
    • if bonds between the R groups on individual amino acids are broken, the protein will stop working properly and is denatured
    • if a protein is denatured:
      shape+function is lost
      it become non functional
    • conditions causing proteins to denature:
      pH unstable
      temp too high
    • at cold temps the enzymes don’t work as fast but are still working
    • fibrous denatured enzymes:
      • lose structural strength
    • Globular denatured enzymes
      • insoluble + inactive
      • they become non functional which is permanent
    • chemical test for protein:
      • add biuret reagent (sodium hydroxide + copper sulfate)
      • the sodium hydroxide provides alkaline environment so the test can work
      • blue to lilac, protein is present
      • negative test is blue
    • in a test for proteins, de-ionised water would be tested as well for a control experiment, as there is no protein just H and O
    • During a protein chemical test, the pH of the tests may be measured after because the test can only work in alkaline conditions
    • During a protein chemical test, the pH of the tests may be measured after because the test can only work in alkaline conditions
    • During a protein test, have to make sure there is enough sodium hydroxide for ALKALINE conditions !!!!
    • Tertiary
      • additional bonds forming between the R groups (side chains)
      • The additional bonds are:
      • Hydrogen (these are between R groups)
      • Disulphide (only occurs between cysteine amino acids)
      • Ionic (occurs between charged R groups)
      • A polypeptide chain will fold differently due to the interactions (and hence the bonds that form) between R groups. The three-dimensional configuration that forms is called the tertiary structure of a protein