Download Amino Acids in Principles of Biochemistry - Study Guide | BC 351 and more Study notes Biochemistry in PDF only on Docsity! Lecture 2 Amino acids The building blocks of proteins Amino acids are α-amino substituted carboxylic acidsamino substituted carboxylic acids 20 naturally occurring amino acids in proteins Incorporated while the protein is being made Encoded in genome A residue is an amino acid in the context of a protein General structure of an amino acid α-amino substituted carboxylic acidscarbon (C-amino substituted carboxylic acidsα), central carbon 4 different groups bound to it α-amino substituted carboxylic acidsamino group NH3 + @ pH 7 (biological setting) α-amino substituted carboxylic acidscarboxyl group COO-amino substituted carboxylic acids @ pH 7 Proton R group Similar to figure 3 – 3a The R – group (aka side chain) is the group that differentiates the 20 amino acids Carbons labeled (β, γ, δ, ε) Amino acid stereochemistry A chiral center is an atom with 4 different groups bound to it 2 different ways to arrange groups around a chiral center Stereoisomers are chemical compounds that have the same chemical make-amino substituted carboxylic acidsup and connectivity but different spatial arrangements Glycine is the only amino acid that does not exhibit stereochemistry Only L amino acids are used in proteins The twenty amino acids Nomenclature: Glycine, Gly, G Table 3 – 1 Grouped based on nature of side chain Nonpolar, aliphatic R groups Aliphatic – hydrocarbon chain; opposite of aromatic Glycine, alanine, proline, valine, leucine, isoleucine, methionine Glycine does not have stereochemistry Glycine is conformationally flexible Proline is least conformationally flexible amino acid For the most part, nonpolar environments – protein interior Aromatic R groups Phenylalanine, tyrosine, tryptophan Phenylalanine – very hydrophobic Tyrosine and tryptophan have hydrophilic sections Polar, uncharged R groups Typically found on protein exteriors Serine, threonine, cysteine, asparagine, glutamine Cysteine is only amino acid that can form covalent bonds with other amino acids Figure 3 – 7 Disulfide bond/bridge Positively charged R groups Lysine, arginine, histidine
