Amino Acids - Elements of Biological Chemistry - Slides | BICH 303, Study notes of Biology

Download Amino Acids - Elements of Biological Chemistry - Slides | BICH 303 and more Study notes Biology in PDF only on Docsity! Amino acids - The building blocks of proteins. - Linked together by peptide bond (amide) to form protein. - Order (sequence) of amino acids critical to protein function individual aa same # & make-up of aa but not same protein Amino acids General structure of an amino acid: Amino acid structure: - stereochemistry (3 -D structure) is tetrahedral - amino group ( -amino group) - carboxyl group - side chain (R-group). determines the identity of the aa. - hydrogen all are bound to: - -carbon Amino acids based on R group (side chain) Non-polar or hydrophobic Polar, uncharged acidic Basic Table 3.1 Amino Acid Three-Letter Abbreviation One-Letter Abbreviation Alanine Ala A Arginine Arg R Asparagine Asn N Aspartic acid Asp D Cysteine Cys Cc Glutamic acid Glu E Glutamine Gln Q Glycine Gly G Histidine His H Isoleucine lle I Leucine Leu L Lysine Lys K Methionine Met M Phenylalanine Phe F Proline Pro P Serine Ser Ss Threonine Thr Hk Tryptophan Trp W Tyrosine Tyr ¥ Valine Jal V © 2006 Brooks/Cole - Thomson Amino acid R groups (side chain) Primarily classified based on: - polar or nonpolar - acidic or basic Other considerations: - additional functional groups on side chain Non-polar (hydrophobic) Non-polar: - most side chains are aliphatic (no aromatic ring) L, P, A, V, M, I - W and F have aromatic ring - M contains sulfur Acid base properties of Amino Acids - At neutral pH both carboxyl and -amino groups of an amino acid are charged, carboxyl “-”, -amino “+” - As pH of solution containing aa goes from acidic to basic the aa functional groups will react with H+ thus changing its charge. - Thus, amino acids are diprotic acids; two pKa’s in two buffer regions. - Have different charge at different pH. - An amino acid with an uncharged side chain exist at neutral pH with no net charge. Example: alanine C HH3N + CHOOH CH3 Alanine R group Acid base properties of Amino Acids Isoelectric point (pI): pH at which the amino acid net charge is zero pI = pKa1 + pKa2 2 What is the pI of Ala? pI = pKa1 + pKa2 2 pI = 2.34 + 9.69 2 pI = 6.02 Acid base properties of Amino Acids Amino acids with charged side chains change net charge at several different pH values. Example: histidine For pI, use pKa on either side of form with zero net charge: pI = pKa1 + pKa2 2 pI = 6.00 + 9.17 2 pI = 7.58 The peptide bond Directionality of peptide bond: - the N-terminal amino acid has free amino group (first aa, on left side when writing peptide sequentially) What is the order of a peptide containing: Alanine (A), Lysine (K), and Histidine (H)? A-K-H A-H-K K-A-H K-H-A H-A-K H-K-A - the C-terminal amino acid has free carbonyl group (last aa, on right side when writing peptide sequentially) Biologically active peptides Dipeptides: - carnosine, Ala-His - found in high concentration in muscle and brain - function not fully understood Nonapeptides: Oxytocin: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly both regulate muscle contraction Oxytocin: during child birth in uterine muscle Vasopressin: regulates blood pressure by controlling smooth muscle contraction. Tripeptides: - glutathione, Glu-Cys-Gly - an antioxidant, protects cells from toxins such as free radicals Biologically active peptides Aspartame: artificial sweetener in diet drinks - Dipeptide of Asp-Phe with methyl group at C-terminus - 200 x sweeter than sugar Asp Phe