Amino Acids, Peptides, and Proteins

Introduction to Amino Acids  There are about 26 amino acids, many others are also known from a variety of sources.  Amino acids are the building blocks used to make proteins and peptides.  The different amino acids have a variety of structural parts which result in different polarities and solubilities.  Each amino acid has at least one amine and one acid functional group  The amino group may be at α or β or γ positions relative to the carboxyl group

Amino acids as zwitterions  Due to internal transfer of a proton from the -COOH group to the -NH 2 group the amino acid has both a negative charge at the carboxylate group and a positive charge at the ammonium group. This salt-like ion is called a zwitterion.  Amino acids are crystallin solids with relatively high melting points due to this salt-like nature  In solutions the charge of the amino acid changes

Classification of Amino Acids  There are basically four different classes of amino acids determined by different side chains: 1.Non polar /Neutral R = H, CH 3, alkyl groups, aromatic 2.Polar / Neutral contain polar groups R contain polar groups –CH 2 OH, –CH 2 SH, –CH 2 CO–NH 2 3.Polar/Acidic R contain –COOH group 4.Polar/ Basic R contain –NH 2 group

Non polar /Neutral Amino Acids 1) Non polar /Neutral Amino Acids Glycine Alanine Valine Leucine Isoleucine Phenylalanine Proline

serine Threonine Cysteine Methionine Polar /Neutral Amino Acids 2) Polar /Neutral Amino Acids Tyrosine Asparagine Glutamine Tryptophan

Polar /Basic Amino Acids 3) Polar /Basic Amino Acids Histidine Lysine Arginine

Polar / Acidic Amino Acids 4) Polar / Acidic Amino Acids Aspartatic acid Glutamic acid

Configuration of Amino Acids  Most of the naturally occurring amino acids have L- configuration while naturally occurring carbohydrates have the D configuration

Proteins and peptides  Proteins are the basis for the major structural components of animal and human tissue.  Proteins are natural polymer molecules consisting of amino acid units linked together by amide or peptide bonds  The number of amino acids in proteins may range from two to several thousand.

Formation of a Peptide  Amide bond is formed between the –COOH of an amino acid and the –NH 2 of the next amino acid

Polymerization  A condensation reaction between the carboxyl of one amino acid and the amino group of another forming a an amide linkage known as peptide bond.  This polymerization is used to form peptides, proteins and enzymes  Peptides Oligopeptides − condensation of 2 – 10 AA unitsOligopeptides − condensation of 2 – 10 AA units Polypeptides − condensation of 11 – 100 AA unitsPolypeptides − condensation of 11 – 100 AA units  Proteins − more than 100 AA units Reactions of Amino acids

The Strecker synthesis Synthesis of Amino acids

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