Protein Structure: Amino Acids

Protein Structure: Amino Acids

1. 20 different alpha AAs

   • Basic and acidic groups
     • Affect properties in water
     • Facilitate polymerisation
   • R-group functionalised in different ways
     • vast array of properties to proteins
   • 19 AAs are chiral
     • All proteins are chiral

2. pH effects on AAs

   • Zwitterion: AA at neutral pH: protonated amide and deprotonated carbonyl
   • Acidic: carbonyl and amide protonated
   • Basic: carbonyl and amide deprotonated

3. Peptide bond: condensation reaction between amide and carbonyl group on 2 AAs, peptide and water formed in reaction

   • Polypeptide: >10 AAs linked
   • Cis and Trans peptide bonds
     • Trans due to steric hinderence

4. Peptides are flexible

   • Free rotation around single bonds
     • But 75% of possible bond conformations are subject to steric hinderence

5. R-side chain

   • Basic
     • Important in enzyme active site
     • Readily accept protons
   • Acidic
     • Readily donate protons
     • Important in enzyme active sites
   • Hydrophobic
     • 9 AAs
     • Structural role : mantain hydrophobic core
     • 2 subgroups
       • Aliphatic (7 AAs)
       • Aromatic (2 AAs)
   • Hydrophillic
     • Hydroxylated groups
     • Carboxamides
     • Polar but don't readily accept or donate protons
     • Form hydrogen bonds, important in structure and interacting with water