Amino acid

Revision cards for Amino acids section of AQA unit 4 syllabus

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Amino Acids have acid and base properities

  • General formular
    • H2NCHRCOOH
      • other than glycerine all amino acids are chiral
  • Carboxylic group has a tendency to lose a proton
    • -COOH --(eqm)--> -COO- + H+
  • amine group has tendency to accept a proton in strongly acidic conditions
    • H+ + -NH2 --(eqm) --> -NH3+
  • Amino acids can exist and Zwitterion
    • H3NHCRCOO
    • High melting points as they are ionic
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Proteins and formation of peptide links

Proteins are sequences of amino acids joined by peptide links

  • H2NHCRCOOK + H2NRCHCOOH --> H2NCONHRCHCOOH + H2O
    • the two amino acids are linked by a peptide bond.
    • can react again to form large peptide chains
    • The above reaction is a condensation reaction (H2O eliminated).
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Hydrolysis of peptide links produce original amino

when a protein or peptide is boiled with HCl acid of conc 6 mol dm-3 for about 24 hours it breaks down to a mixture of amino acids.

Acid hydrolises the peptide links

  • H2NRCHCONHRCHCOOH +H2O --(H+ catalyst)--> 2H2NRCHCOOH

These amino acid mixtures can be separated by chromatography.

  • allows us to find out which ones are present
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Hydrogen bonding in proteins

Complex structures in proteins held together by hydrogen bonding

Shapes of proteins vital to function (e.g. enzymes and active site!)

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