Chapter 17 Notes

Chapter 17 Notes - -An amino acid can never exist as an...

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Chapter 17 Notes – Amino Acids, Peptides, and Proteins 17.1 – Classification and Nomenclature of Amino Acids - Ten amino acids are essential, in which the body cannot not synthesize so must be supplemented through diet - Most amino acids are called by their common names and have three-letter abbreviations 17.2 – Configuration of Amino Acids - The α-carbon of all the naturally occurring amino acids, except glycine, is an asymmetric center - A Fischer projection with the amino group on the right is a D -amino acid and with the amino group on the left an L -amino acid - Naturally occurring amino acids are L -amino acids 17.3 – Acid-Base Properties of Amino Acids - The carboxyl groups of the amino acids have pK a values of approximately 2, and the protonated amino groups have pK a values near 9
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Unformatted text preview: -An amino acid can never exist as an uncharged compound, regardless of the pH of the solution-It would have to lose a proton from + NH 3 before it could lose one from COOH, which would be like a weak acid being more acidic than a strong acid, which is clearly not possible 17.6 Peptide Bonds and Disulfide Bonds -Peptide and disulfide bonds are the only covalent bonds that hold amino acids together -Peptide Bonds o The amide bonds that link amino acid residues are called peptide bonds o A peptide bond has partial double-bond character because of electron delocalization which prevents free rotation -Disulfide Bonds o When thiols are oxidized under mild conditions, they form disulfides, which are compounds with SS bonds o Disulfides can be reduced to thiols...
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