Tiêu đề [POST LAB DISCUSSIONS] Pharmaceutical Biochemistry ✅

CEBU DOCTORS’ UNIVERSITY COLLEGE OF PHARMACY PHARMACEUTICAL BIOCHEMISTRY POST LABORATORY DISCUSSIONS EXPERIMENT NO. 1 PROTEINS Activity 1.A — Elementary Composition of Protein (1) Carbon, Hydrogen, Oxygen (heating casein) Answer: ● d) Upper, cooler part: Water droplets (condensed steam) ● e) Carbon (from charring); Hydrogen and Oxygen (from water formation) Heating casein causes thermal decomposition. Volatilized water condenses at the tube’s cool top (so you see droplets), proving H and O; the dark char is carbonaceous residue, showing C is present. (2) Test for Nitrogen (soda-lime) Answer: Gas is ammonia (NH3); red litmus turns blue, blue litmus stays blue; ammoniacal odor. Hot soda-lime (NaOH/CaO) deaminates nitrogenous groups in proteins → NH3(g). Ammonia in moist air forms NH4OH, a base that turns red litmus blue and has a pungent smell. (3) Test for Sulfur (alkaline lead acetate) Answer: ● e) Black precipitate ● f) Lead(II) sulfide (PbS) Boiling albumin with NaOH breaks S–S/–SH (e.g., cystine/cysteine) → Na2S. Adding Pb2+ (lead acetate) gives PbS (black): Na2S + Pb(CH3COO)2 → PbS↓ + 2 CH3COONa. (4) Test for Phosphorus (nitric acid → ammonium molybdate) Answer: ● e) Yellow precipitate ● f) Ammonium phosphomolybdate ● g) Formation of that yellow precipitate indicates phosphorus (as phosphate) Oxidation with HNO3 converts organic P → PO43−, which reacts with ammonium molybdate to give a yellow phosphomolybdate complex. 1


● Alkaloids: Naturally occurring basic nitrogenous organic compounds (often plant-derived). ● Alkaloidal reagents: Strong acidic precipitants (e.g., picric/tannic/phosphomolybdic/phosphotungstic acids; potassium mercuric iodide) used to precipitate basic compounds; also precipitate proteins by forming insoluble complexes at cationic sites. EXPERIMENT NO. 2 ISOLATION AND COLOR REACTIONS OF PROTEINS Activity 2.A: Isolation of Protein 1. Isoelectric Precipitation of Protein (Casein) ● Procedure: ○ Acidifying the milk solution with HCl to a pH of 4.6 causes casein (the main protein in milk) to precipitate, as it reaches its isoelectric point where the protein’s net charge is zero, making it insoluble in water. ● Casein is the protein precipitated at pH 4.6. The precipitation occurs because at the isoelectric point, the protein molecules aggregate and form an insoluble network due to the lack of charge repulsion. 2. Isolation of Gluten ● Procedure: ○ Kneading wheat flour with water removes the starch and isolates gluten, which is a protein complex. ● Gluten is isolated from wheat flour. ● Gluten is insoluble in water but is soluble in dilute alkaline solutions. The kneading process removes starch, leaving gluten as the residue. 3. Isolation of Bean Protein ● Procedure: ○ Soaking beans and grinding them with water allows the protein to precipitate upon the addition of acetic acid. ● Bean Protein is isolated by precipitation with acetic acid. ● Acidifying the solution causes proteins (such as globulins) to precipitate out of the solution, as they become insoluble at low pH. 4