UNIT 9 CS 26-27 THE CHEMISTRY OF PROTEINS

Learning Objectives Define proteins and state its composition. State the biomedical importance of proteins. Describe the classification of proteins with suitable examples. Explain the denaturation of proteins

What are Proteins? Derived from Greek word “proteios” means primary Are high molecular weight substances About half the dry weight of living materials is proteins. Composition of Protein: C,H,O (present in carbohydrate) + N CHON (Protein)  macro molecules Polymers – chainlike molecules linking together of a number of small units (amino acids).

PEPTIDE BONDS (C-O-NH-) DIPEPTIDE POLYPEPTIDE TRIPEPTIDE TWO AMINO ACIDS ARE JOINED TOGETHER LARGE NUMBER OF AMINO ACIDS GLYCINE, ALANINE & SERINE

BIOMEDICAL IMPORTANCE OF PROTEINS Main dietary constituents for supply of nitrogen and sulphur Immunoglobulins are the frontline of defence against bacterial and viral infections Muscular proteins provide us with mechanical movement Acts as receptors (proteins present in cell membrane, nucleus and cytoplasm) Proteins help to maintain water & electrolyte balance. Biochemical catalysts (enzymesproteins) As storage protein (Iron is stored as ferritin) Constituents of respiratory pigments (cytochromes, myoglobulin, hemoglobin)

4 LEVELS OF ORGANIZATION STRUCTURE OF PROTEINS 4 LEVELS OF ORGANIZATION PRIMARY Amino acid sequence TERTIARY Three dimensional structure QUARTERNARY Polymeric protein SECONDARY Polypeptide chain “repetitive”

Denaturation of Proteins If protein is exposed to different set of environment conditions  alteration in physical properties and its ability to perform its biological role. HIGH TEMPERATURE PROTEIN DENATURED PROTEIN EXTREME PH LOSS OF BIOLOGICAL ACTIVITY Example of Denaturation Boiling of an egg Formation of cheese

Example of Denaturation of Proteins HIGH TEMPERATURE RAW EGG WHITE (Globular Protein) HARD EGG WHITE (Fibrous Protein) BOILING

Example of Denaturation of Proteins COAGULATION

CLASSIFICATION OF PROTEINS (As Per Solubility) COLLAGENS Bone, teeth, tendon, skin KERATINS Hair, nails FIBRIN Blood clot MYOSINS Muscles ELASTINS Found in ligaments PROTEINS FIBROUS Fribrous proteins are insoluble in water.

CLASSIFICATION OF PROTEINS (As Per Solubility) GLOBULAR PROTEINS (Soluble in water) 1. ALBUMINS Found in egg white and blood. Functions: Buffers Carries lipids, metal ions & fatty acids 2. GLOBULINS Function: Defense against disease.

CLASSIFICATION OF PROTEINS (As Per Composition) Nutritional Point of View Complete Proteins (e.g. egg, albumin, casein milk) Partially incomplete proteins Incomplete proteins

CLASSIFICATION OF PROTEINS (3 Groups as per Composition) SIMPLE PROTEINS DERIVED PROTEINS CONJUGATED PROTEINS Amino Acids Only Amino Acids + Non Protein Compound Polypeptides Dipeptides

CONJUGATED PROTEINS GLYCOPROTEINS Protein + sugar E.g. Gamma globulin HEMOPROTEINS Protein with heme units E.g. hemoglobin, myoglobin and cytochromes (enzyme that help cell use Oxygen) LIPOPROTEINS Protein with lipid molecules including cholesterol METALLOPROTEINS Incorporates a metal ion E.g. enzymes

CONJUGATED PROTEINS NUCLEOPROTEINS Bound to nucleic acids E.g. ribosomes & viruses PHOSPHOPROTEINS With phosphate ester E.g. serine (casein)

DERIVED PROTEINS (As per Biological Function) Enzyme: the body catalysts Contractile muscle: myosin (stationary filament) & actin (moving filament). Hormones: growth hormones, insulin Neurotransmitters: Eukephalins, endorphins Storage proteins: seed protein in grains, casein in milk, albumin in egg white, ferritin in iron storing protein human spleen. Transport proteins: Haemoglobin, serum albumin

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