Amino Acids Peptides BIOMEDICAL IMPORTANCE the monomer units
Amino Acids & Peptides
BIOMEDICAL IMPORTANCE • the monomer units – L-α-amino • Cellular functions – Nerve transmission – Biosynthesis of porphyrins – Purines – Pyrimidines – Urea
Biomedical Importance • Peptides – Neuroendocrine system • as hormones, • hormone-releasing factors, • Neuromodulators, or neurotransmitters
• One- & three-letter • Additional amino acids arise by modification – methylation, formylation, acetylation, prenylation, and phosphorylation
L- α-Amino acids present in proteins.
• Amino Acids May Have Positive, Negative, • or Zero Net Charge
• Zwitterions – equal number of ionizable groups of opposite charge • p. Ka – Express the Strengths of Weak Acids
Protonic equilibria of aspartic acid.
• The net charge on an amino acid – Depends upon the p. Ka values of its functional groups – the p. H of the surrounding medium • At Its Isoelectric p. H (p. I), an amino acid bears no net charge
the p. I for aspartic acid For lysine, p. I is calculated from:
Typical range of p. Ka values for ionizable groups in proteins.
Amino Acid Sequence Determines Primary Structure
Peptide Structures
• Some Peptides Contain Unusual Amino Acids
Glutathione (γ-glutamyl-cysteinylglycine). Note the non-α peptide bond that links Glu to Cys.
• Peptides Are Polyelectrolytes • The Peptide Bond Has Partial Double-Bond Character
The four atoms of the peptide bond (colored blue) are coplanar
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