Th1L03 Amino acids

Th1L03 Amino acids

1. Building block of proteins

2. Structure

   • Central carbon atom (alpha-carbon) linked to an amino group, a carboxylic group, a hydrogen atom and a R group (variable group)
   • Chiral
     • Can exist in two mirror-image forms
       • L and D isomers
         • L isomer has amino group on left side
           • Only L amino groups are constituents of proteins probably because are more soluble
         • D isomer has amino group on right side

3. Dipolar ions or zwitterions

   • Amino acids at neutral pH
   • Amino group is protonated (-NH3+)
   • Carboxyl group (-COO-) is deprotonated
   • Ionisation sates of an amino acid depends on pH

4. In acidic solution

   • amino acid group(-NH3+)
   • carboxyl group (-COO-) is deprotonated

5. In basic solution

   • carboxyl group tends to be the first group to give up its proton as it has a low pKa (approx . 2)
   • The dipolar form persists until pH = 9 where the protonated amino group loses a proton

6. Functional groups

   • include alcohols, thios, thioesters, carboxylic acids, carboxamides and various basic groups
   • Most are chemically reactive and account for protein function
     • Size, shape, charge, hydrogen bonding capacity, hydrophobic character, chemical reactivity
     • Reactive properties of functional groups are essential to enzymes
       • Proteins can interact with one another and with their biological macromolecules which have more complex functions
   • Proteins differ in their rigidity/ flexibility and this plays a role into function (think cytoskeleton vs. connective tissue)

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