Proteins q Are the most diverse biomolecules They

Proteins q Are the most diverse biomolecules. They make up muscles, skin, hair, enzymes, hormones, hemoglobin, and antibodies. q The basic structure unit of protein is amino acid Amino group Side Chain Carboxylic Acid group

q In the solid state amino acids exist in the dipolar form

q. The side chains are what differentiate amino acids. q. The side chains can be divided into four categories: 1. Non polar 2. Polar Neutral 3. Polar Basic 4. Polar Acidic

Non polar

Polar Neutral

Polar Basic

Polar Acidic

Protein Formation q. Amino acids are joined together to form protein when the carboxylic end of one amino acid reacts with the amino end of another amino acid to form a protein. q. This link between the two amino acids is called Peptide Bond.

Protein Structure q. Described in terms of four levels of organization: 1. Primary Structure 2. Secondary Structure 3. Tertiary Structure 4. Quaternary Structure

Primary Structure q A sequence chain of amino acids (Insuline)

Secondary Structure q. Occurs when the sequence of amino acids are linked by hydrogen bonds (hair, wool) Hydrogen bond between every N-H group and the oxygen of C=O group in the next turn of the helix Hydrogen bond between The amides group of linear polypeptide

Tertiary Structure q. The folding of α-helix and the β-plated sheet of the secondary structure Maintained by Hydrogen bonds, Ionic bonds, Disulfide Linkages And Dispersion forces between side chains

Quaternary Structure q. Two or more polypeptide subunits join together to form the quaternary structure.

Classification of Proteins q. Classification according to solubility: 1. Fibrous Proteins: • In soluble in water • Example: Collagen (bones and teeth), Keratins (hair and wool), Myosins (contractile muscles), Fibrin (protein of blood clot)

Classification of Proteins 2. Globular proteins • Soluble in water • Examples: Albumin (egg white and blood), Globulins (antibodies, enzymes)

Classification of Proteins q. Function in the body 1. Building of new cells 2. Valuable source of energy 3. Catalysis biochemical reactions (enzymes) 4. Transportation of Oxygen (hemoglobin) 5. Bodies defense against infection (antibodies) 6. Transmission of impulses (nerves)

Denaturation of Proteins q. Occurs when there is a disruption of the bonds that stabilize the secondary, tertiary or quaternary structures of proteins. q. When this occurs, the protein unfolds and is no longer biologically active. q. Denaturation is occurred by: 1. heat 2. acids and bases 3. organic compounds 4. heavy metal ions

Physical Properties 1. Solubility 2. Power of hydrogen ion • p. H near 7 because there is COOH (acid) and NH 3 (base) • Proteins are amphoteric compounds, can react with acids and bases.

Chemical Properties 1. Buret test • General test for proteins.

2. Xanthoprotic test Identify proteins with aromatic ring +ve result yellow add Na. OH orange 3. Millon’s test To distinguish the presence of phenolic hydroxyl group +ve test white ppt heat brick red

4. Ppt of proteins with alcohols 5. ppt of proteins with acids