biochem lab

• Colloid


  Suspension of particles that are larger than true solutions but still smaller to settle out by gravity. They cannot be filtered by ordinary filters.
• Colloidal system


  • Consists of two components: dispersed phase and dispersion phase
• Dispersed phase


  Macromolecular solids like proteins and nucleic acids, and liquids like oily fats
• Dispersion phase


  The medium in which insoluble materials are dispersed. It may be solid, liquid or gas.
• Suspensoid


  Lyophobic colloid where water is the dispersing medium but the suspended particles have little or no affinity toward water. Stability depends on electric charge.
• Emulsoid


  Lyophilic colloid which hydrates readily and has affinity between the dispersed phase and dispersion medium. Can have positive, negative or no electric charge.
• Dialysis


  Solvent molecules, small molecules and hydrated ions pass from a solution through a semipermeable membrane. Colloid particles and large molecules are held back.
• Dialyzing membranes


  • Have larger pores than osmotic membranes, allowing solvent, hydrated ions and small molecules to pass through while holding back colloid particles and large molecules.
• Types of dialysis membranes

  • Cellulose-based (PES, PAN, PVDF), regenerated cellulose-based, composite
• Adsorption


  Process where a solid (activated charcoal) is used to remove a soluble substance (like methylene blue dye) from water.
• Adsorption process


  • Involves adsorbent (activated charcoal) and adsorbate (liquid molecules). Can be physisorption or chemisorption.
• Methylene blue dye is difficult to biodegrade when discharged into water, so adsorption is an effective treatment option.
• Osmosis


  Spontaneous flow of solvent through a semipermeable membrane from a solution of low concentration to one of higher concentration.
• Physiological activities like absorption from gastrointestinal tract and fluid interchange in body follow the principle of osmosis.
• Diffusion alone, without convection currents and gravity, is very difficult to demonstrate in liquids.