PROTEINSImportance, Characteristics,

Structure, Classification, Denaturation

IMPORTANCE 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

CHARACTERISTICS 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

STRUCTURE OF PROTEINS 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.

CLASSIFICATION 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

CLASSIFICATION 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 Denaturation – unfolding of the complex

secondary, tertiary and quaternary structure of proteins

PROTEIN DENATURANTS 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

PROTEIN DENATURANTS 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