Amino Acids

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Amino Acid Structure

H                       R                       O

         N              C           C

H                       H                      OH

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Formation of a Dipeptide

H                         R1                         O      H                        R2                            O

           N              C             C                                N             C                C

H                         H                           OH   H                          H                              OH

                           Condensation                          -H2O

     H                       R1                 O                  H                     R2                       O

               N             C                   C                  N                     C             C     

    H                        H                                                              H                         OH

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Functions of proteins

  • Membrane carriers and pores e.g. active transport, facilitated diffusion
  • Many hormones are proteins
  • Provid building materials important for growth and repair
  • Crucial to most metabolic activity
  • Antibodies are proteins
  • Enzymes are proteins
  • Structural Components e.g. muscle and bone
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Ionic Interactions and Disulphide Bridges (cystein

  • R-groups sometimes carry a charge, either +ve or -ve
  • Where oppositely charged amino acids are found close together / to each other an ionic bond forms
  • Ionic bond between ionised r-groups

              R    -------- R     


  • The amino acid cysteine contains sulfure
  • Where two cysteines are found close to each other a covalent bond can form
  • Disulphide bond between R-groups containing -SH groups

                   S              S

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Hydrogen Bonds and Hydrophobic Interactions

  • As in secondary structure
  • Wherever slightly positively charged groups are found close to slightly negatively charged groups hydrogen bonds form.
  • Hydrogen bond

       N            H ---------O = C


  • In water based environment hydrophobic amino acids will be most stable if they are held together with water excluded
  • Hydrophilic amino acids tend to be found on the outside in globular proteins, with hydrophobic amino acids in the centre
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