BioChem Ch. 3 Amino acids and Peptides

BioChem Ch. 3 Amino acids and Peptides - 4. Peptide bond...

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CHapter 3- Amino Acids and Peptides I. The Amino Acids in Proteins A. General structure of amino acids 1. alpha-carbon a. hydrogen b. carboxyl group c. amino group d. side chain (variable) 2. Side Chain (R-group) determines reactivity 3. Chiral alpha-carbon (except glycine) a. D-and L- amino acids (enantiomers) b. only L-isomers used to make proteins in nature B. Classification of amino acids based on R-groups (side chains) 1. Nonpolar (hydrophobic) 2. Polar and Neutral 3. Charged-Acidic 4. Charged -Basic Know Table 3.1 C. Properties of Amino Acids 1. White, crystalline solids 2. High melting points 3. Water-soluble 4. Dipolar ionic species at pH 7.4 (Zwitterion) a. aqueous solutions conduct electricity b. Behave like salts (ionic compounds) 5. Acid-base properties a. Predicting electrical charges at a given pH
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b. pKa values (Table 3.2) c. Titration curves D. Reactivity 1. Acid-base reactions 2. Ester formation (Ser, Thr, and Tyr) 3. Disulfide bond formation (Cys)
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Unformatted text preview: 4. Peptide bond formation II. Peptides A. Peptide Bond Formation 1. Condensation reaction 2. Residue: single amino acid 3. Polypeptide: 10-100 amino acids 4. Protein: more than 100 amino acids B. Molecular Weights 1. Average MW of amino acid=110 2. MW of proteins = 220-220,000 1 amu = 1 dalton C. Termini 1. Amino (N-terminus) 2. Carboxyl (C-terminus) D. The chemical and physical properties of proteins depend on their amino acids. 1. Determining net charge at a given pH a. Use pKa values to obtain charges on side chains b. Include charges at termini c. add charges 2. Microenvironment can affect properties of nearby side chains 3. Isoelectric point (pl) = pH when molecule has no net charge E. Physiologically Active Peptides 3aa 1. Glutathione -scavenger for oxidizing agents 5aa 2. Enkephalin - brain (pain relievers) 3. Oxytocin - contraction of uterus : milk flow 9aa 4) Vasopressin - blood pressure...
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BioChem Ch. 3 Amino acids and Peptides - 4. Peptide bond...

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