amino acids & peptides. biomedical importance the monomer units – l-α-amino cellular...
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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
• pKa – Express the Strengths of Weak Acids
Protonic equilibria of aspartic acid.
• The net charge on an amino acid – Depends upon the pKa values of its functional
groups– the pH of the surrounding medium
• At Its Isoelectric pH (pI), an amino acid bears no net charge
For lysine, pI is calculated from:
the pI for aspartic acid
Typical range of pKa values forionizable groups in proteins.
Amino Acid Sequence DeterminesPrimary Structure
Peptide Structures
• Some Peptides Contain Unusual Amino Acids
Glutathione (γ-glutamyl-cysteinylglycine).Note the non-α peptide bond that linksGlu 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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