Importance, Characteristics, Structure, Classification, Denaturation

 Major structural components of animal tissues  Involved in the maintenance of life processes as communication (nerves), defense (antibodies), metabolic regulation (hormones), biochemical catalysis (enzymes), and oxygen transport (hemoglobin)  Utilized in the building of new tissues and maintaining tissues which are already developed

 Unlike fats and carbohydrates, proteins are not stored to any appreciable extent  They are giant polymers whose MW ranges from several thousands to millions  The elementary composition of most proteins are 55% C; 7% H; 23% O; 16% N; 1% S; and less than 1% P

 Primary – defined by the number, sequence and kind of amino acid linked by peptide bond  Secondary – any ordering of otherwise flexible peptide chain resulting from the formation of H- bonds between the carbonyl oxygen and the amide nitrogen of the polypeptide backbone  Tertiary – superfolding of the protein due to interactions between the different Rs of the amino acid  Quaternary – intermediate interactions between protein molecules which are folded and refolded can yield aggregates of individual molecules.

 According to Shape - Globular – more or less spherical to oblate or egg-shaped (Ex. Insulin, myoglobin) - fibrous – individual strands or bundles of lateral strands, elongated molecules highly resistant to digestion by proteolytic enzymes (Ex. Elastin and collagen, keratins, myosin, fibrin

 According to Function - Structural (collagen) - contractile proteins (myosin and actin) - antibodies (gamma globulins) - oxygen binding proteins – blood proteins or transport proteins - hormones - enzymes - nutrient protein

 Denaturation – unfolding of the complex secondary, tertiary and quaternary structure of proteins

 Heat – causes the atoms within the protein molecule to vibrate more rapidly, causing the hydrogen bonds and hydrophobic interactions to break  Strong acids – split salt linkages by ionizing the carboxylic group  Alcohol – disrupts the hydrogen bonds  Heavy metals (Ag, Pb and Hg) – combines the free carboxylate anions of the acidic amino acid with the metal, causing precipitation

 Organic acids (picric and tannic acids) – used to precipitate the alkaloids giving rise to the name alkaloidal reagents. The anion of the acid will react with the protonated amino groups of proteins, causing disruption of the salt linkages