Amino Acid

Amino Acid

1. Building blocks

2. 20 common amino acids

   • based on polarity of sidechains
   • Non polar and Hydrophobic
     • Alanine (Ala, A)
     • Valine (Val, V)
     • Leucine (Leu, L)
     • Isoleucine ( Ile, I)
     • Proline (Pro, P)
     • Methionine (Met, M)
     • Phenylalanine (Phe, F)
     • Tryptophan (Tryp, W)
   • Polar and Hydrophilic
     • uncharged
       • Glycine
         • not a good H bond former
       • Serine (ser, S)
       • Threonine (Thr, T)
       • Cysteine (Cys, C)
       • Asparagine (Asn, N)
       • Glutamine (Gln, Q)
       • Tyrosine (Tyr, Y)
       • R group can form H bonds w/ h2o
       • buried as well as on the surface of protein
     • charged
       • acidic
         • Aspartic acid (Asp, D)
         • Glutamic acid (Glu, E)
       • Basic
         • Lysine (Lys, K)
         • Arginine ( Arg, R)
         • Histidine (His, H)
         • R' group are weaker acids than a-COOH
         • contained in metal binding sites
         • -COOH act as nucleophiles
       • can be important in the recognition of oppositely charged groups

3. special features

   • able to polymerize
   • acid base properties
   • chirality (mirror image)
     • L-isomer
     • D-isomer

4. Tetrahedral structures (except proline and its derivatives)

5. Zwitterion

   • pH 7
   • 0 nett charge

6. Formation of peptides

   • condensation
     • formation of peptide bond
   • Numbering and naming
     • Full names
     • 3 letter code
     • 1 letter code

7. Uncommon amino acids in protein

   • Selenocysteine (Sec)
   • Pyrrolysine (pyl)
   • Less common
     • Hydroxylysine and hydroxyproline
       • collagen and gelatin proteins
     • Pyroglutamic acid
       • Halobacterium halobium
     • Aminoadipic acid

8. Non - protein amino acids

   • Y- aminobutyric acid
     • potent neurotransmitter
   • Histamine
     • decarboxylation of histidine
   • epinephrine (adrenaline)
   • Penicillamine
   • Citrulline

9. Acid-Base properties

   • Dissociation of H from COOH and NH3+