Properties of Amino Acids (DLA)

General Structure of Amino Acids

Amino acids have an asymmetric alpha-carbon atom (except glycine) linked to a carboxylic acid group, an amino group, an H atom, and a variable R group.

Stereochemistry of Amino Acids

Of the 20 common amino acids, 19 are chiral and exist as non-superimposable mirror images (D&L forms). Naturally occurring proteins are composed of L-amino acids.

Charged Side Chain Amino Acids

The amino acids with charged side chains include aspartate, glutamate, arginine, lysine, and histidine.

Amino Acids with Hydroxyl Group

Amino acids containing a hydroxyl group include serine and threonine.

Amino Acids with Sulfur

The amino acids that contain sulfur are methionine and cysteine.

Acid/Base Properties of Amino Acids

Amino acids exhibit acid/base properties; for example, histidine has a side chain with an imidazole ring (pKa ~6) that buffers pH changes in the cell.

Role of Histidine in Buffering

Histidine residues play a role in buffering by maintaining pH around 7 in cells, with a pKa that may shift between 6 and 7 in proteins due to local environments.

Biologically Active Amines Formation

Alpha amino acids serve as precursors for biologically active amines, where the amino group is retained, and the carboxyl group is decarboxylated, as seen in GABA and Histamine.

Importance of GABA

GABA is a neurotransmitter synthesized from glutamate.

Importance of Histamine

Histamine mediates allergic and inflammatory responses and is synthesized from histidine.

Importance of Serotonin

Serotonin regulates pain perception, affect, and sleep; synthesized from tryptophan.

Importance of Catecholamines

Catecholamines (dopamine, norepinephrine, epinephrine) are formed from tyrosine and play roles in neurotransmission and hormonal responses during stress.

Main Features of Peptide Bonds

Peptide bonds form between the alpha-carboxyl group of one amino acid and the alpha-amino group of another, featuring partial double-bond character, rigidity, and planarity.