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