16. α –Amino acids - classification. Chemical properties of α -amino acids. Chemical aspects of amino acid metabolism – deamination of α -amino acids; ketogenic and glucogenic amino acids.

α-Amino acids - structure, nomenclature,

• Amino acids:
• Contain carboxylic acid group (-COOH) and amino group (-NH2).
• Usually α- to the carboxylic acid (means they are attached to adjacent carbon atoms in the molecule).
• Classified as α-, β-, γ-, etc. based on relative positions of functional groups.

• α-Amino acids:
• Most important biologically.
• Amino and carboxyl groups are α- to each other.
• Structures may have various functional groups.
• Classification based on functional groups:
• I. Neutral:
• I.1. Non-polar R-groups.
• I.2. Non-charged polar (non-ionized) R-groups.
• II. Acidic:
• Contain acidic functional groups.
• III. Basic:
• Contain basic functional groups.

Stereochemistry.:

• Amino acids are chiral molecules.
• Except for glycine, which has two identical substituents on the α-carbon, α-amino acids have four different substituents, making them chiral.
• The α-carbon is the chiral center.
• Naturally occurring amino acids predominantly exist in the L-configuration, where the amino group is on the left side when the carboxyl group is at the top.
• The D-configuration also exists but is less common in naturally occurring proteins.
• The stereochemistry of amino acids is crucial for the folding and function of proteins.