Structure and Properties of Amino Acids and Proteins Amino Acids General Features Isomerism, Chirality and Optical Rotation Amphoteric Properties Amino Acid Side Chains Acid Base Characteristics of Amino Acids Peptides and Proteins Levels of Protein Structure Primary Structure Secondary Structure Tertiary and Quaternary Structures How Protein Conformations are Stabilizing

General Amino Acid Structure

General Amino Acid Features -O O C R +H 3 NH C = O O- C R NH 3 +H C = L - isomerD - isomer Isomerism Constitutional isomers, nonsuperimposable, mirror images (i.e. stereoisomers)

General Amino Acid Features -O O C R +H 3 NH C = O O- C R NH 3 +H C = R - clockwise Chirality and the R, S system S - counterclockwise H < C < N < O

General Amino Acid Features -O O C R +H 3 NH C = O O- C R NH 3 +H C = L - isomerD - isomer Amphoteric Properties Zwitterions

Valine Alanine Pyruvate Nonpolar Hydrophobic Amino Acids IsoleucineLeucine Proline

Phenylalanine Tryptophan Tyrosine Aromatic Amino Acids

Aspartic Acid Oxaloacetate Glutamic Acid A-ketoglutarate Metabolic intermediates

Histidine Arginine Lysine Positively Charged Amino Acids

Threonine Asparagine Methionine Serine Cysteine Glutamine Amino Acids with Uncharged R- groups (but vary in polarity) Glycine

Essential amino acids 1.Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. 2.Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in degradation cellular and noncellular proteins to obtain the one amino acid that is needed. 3.Unlike fat and starch, the human body does not store excess amino acids for later use—the amino acids must be in the food every day. 4.The 10 amino acids that we can produce are: AlanineAsparagineAspartic acid CysteineGlutamic acidGlutamine Glycine ProlineSerine Tyrosine Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well.

Proline

The essential amino acids are: Arginine HistidineIsoleucine Leucine LysineMethionine PhenylalanineThreonineTryptophan Valine These amino acids are REQUIRED in the diet. They are INDISPENSABLE.