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 pK a – Express the Strengths of Weak Acids

Protonic equilibria of aspartic acid.

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

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

Typical range of pKa 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