Amino acids and peptides The “Lego” of proteins

Amino Acids Same general structure Called alpha amino acids L- isomer is physiologically active Side chain or R group determines other properties Acid-base properties

Amino Acids, General pK of carboxyl group around 2.3 Deprotonated at physiological pH R – COO- pK of amino group around 9.5 Protonated at physiological pH H3N+-R Some R-groups are acidic or basic

Nonpolar amino acids

Aromatic Amino Acids

Polar Amino Acids, alcohols

Polar Amino Acids (sulfur containing)

Polar amino acids (amides)

Charged Amino Acids (Acidic)

Charged Amino Acids (Basic)

Titration of Amino acids Titration of glycine

Titration of Glutamate

Purification of amino acids Chromatography Various types Ion exchange Uses net charge or can change with pH Separate K, D and A HPLC

Electrophoresis Using electricity to move particles through a gelatinous matrix Isoelectric point IEF

Peptides Peptide bond is amide linkage between amino acids No free rotation about C-N bond due to partial double bond character of bond resonance

Tetrapeptide Note planes of peptide bonds

Peptides Peptides are vectorial Sequences read H3N+---COO- Have N and C termini Sequences read H3N+---COO- P-I-G

Draw a tetrapeptide of L-A-R-D at physiological pH Answer

Biologically Interesting Peptides Aspartame L-aspartyl-Lphenylalanine methyl ester

Other small interesting peptides Enkephalins Y-G-G-F-L Y-G-G-F-M Oxytocin C-Y-I-Q-N-C-P-L-G-NH2 Has C—C disulfide Vasopressin C-Y-F-Q-N-C-P-R-G-NH2 Also disulfide

Chemical Synthesis of Peptides Why? Done solid phase Problem with in solution Hard to make pure desired sequence Purify by filtration Side chains blocked Made backwards ( C---N)

Scheme for peptide synthesis

Tetrapeptide answer Back