Chapter 1: Amino Acids, Peptides, & Proteins

• 20 AA's to know are known as the proteinogenic amino acids (encoded by the human genetic code)
• Glycine is achiral. Cysteine has R absolute configuration. Everyone else is S absolute config.
• only AA with chiral carbon in side chains: threonine and isoleucine
• Nonpolar, nonaromatic side chains: Glycine, alanine, valine, leucine, isoleucine, methionine, proline
• Aromatic side chains: tryptophan, phenylalanine, tyrosine
• Polar side chains: serine, threonine, asparagine, glutamine, cysteine
• Acidic Side Chains: aspartic acid (COOH is delta), glutamic acid (COOH is gamma)
• Basic Side Chains: histidine (aromatic), arginine (lots of N's), lysine
• Hydrophobic: GAVLIP FMW Y Hydrophilic: C STNG
• One-Letter Abbreviations to remember: Aspartic Acid = D, Glutamic Acid = E, Glutamine = Q, Lysine = K
• pH < pKa = protonated. pH > pKa = deprotonated.
• at acidic pH values, AA are + charged. at basic pH values, AA are - charged.
• titration curve of AA looks like a combination of two monoprotic acid titration curves (or three if there is a charged side chain)
• AA with acidic side chains have pI values below 6. AA with basic side chains have pI well above 6
• Peptide bond formation = condensation or dehydration reaction
• Peptide bond: amino group attacks electrophilic carbonyl carbon. C-N has partial double bond character and is stabilized by resonance (super stable!)
• Trypsin and chymotrypsin are hydrolytic enzymes that cleave specific points in the peptide chain (trypsin: carboxyl end of R and K. chymotrypsin: carboxyl end of F, W, and Y)
• 1°: linear arrangement of AA. 2°: result of h-bonding (alpha helices and beta sheets). 3°: 3D shape. disulfide bonds. also mostly determined by hydrophilic or hydrophobic interactions between R groups. 4°: lots of different subunits coming together. can lead to allosteric effects (cooperativity)
• losing 3° structure (aka 3D structure) = denaturation
  • this can ocur using heat or increasing solute concentration