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Amino Acids & Peptides

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BIOMEDICAL IMPORTANCE the monomer units L--amino Cellular functions Nerve transmission Biosynthesis of porphyrins Purines Pyrimidines Urea

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Biomedical Importance Peptides Neuroendocrine system as hormones, hormone-releasing factors, Neuromodulators,or neurotransmitters

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One- & three-letter Additional amino acids arise by modification methylation, formylation, acetylation, prenylation, and phosphorylation

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L- -Amino acids present in proteins.

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Amino Acids May Have Positive, Negative, or Zero Net Charge

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Zwitterions equal number of ionizable groups of opposite charge pK a Express the Strengths of Weak Acids

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Protonic equilibria of aspartic acid.

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The net charge on an amino acid Depends upon the pK a values of its functional groups the pH of the surrounding medium At Its Isoelectric pH (pI), an amino acid bears no net charge

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For lysine, pI is calculated from: the pI for aspartic acid

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Typical range of pKa values for ionizable groups in proteins.

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Amino Acid Sequence Determines Primary Structure

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Peptide Structures

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Some Peptides Contain Unusual Amino Acids

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Glutathione (-glutamyl-cysteinylglycine). Note the non- peptide bond that links Glu to Cys.

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Peptides Are Polyelectrolytes The Peptide Bond Has Partial Double-Bond Character

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The four atoms of the peptide bond (colored blue) are coplanar