Define enzymes as biocatalysts and explain their role in biochemical processes. Provide four examples of industrial processes that utilise enzymes and explain the role of enzymes in each process.

Enzymes are biological macromolecules, primarily proteins, that act as biocatalysts. A biocatalyst is a substance that increases the rate of biochemical reactions without being consumed in the process.

Enzymes accelerate biochemical reactions by lowering the activation energy required for the reaction to proceed. They do this by binding to specific substrates at their active site, forming an enzyme-substrate complex, and facilitating the conversion of substrates into products. This specificity ensures that only particular reactions are catalyzed, maintaining metabolic control within living organisms.

Question 4, Part 2:

Here are four examples of industrial processes that utilize enzymes:

1. Detergent Industry: Enzymes like proteases, lipases, and amylases are added to laundry detergents. Proteases break down protein stains (e.g., blood, grass), lipases break down fat stains (e.g., oil, grease), and amylases break down starch-based stains (e.g., food residues). This allows for effective cleaning at lower temperatures and with less harsh chemicals.
2. Food and Beverage Industry (e.g., Brewing): Enzymes such as amylase and glucoamylase are used in brewing to break down starches in grains into fermentable sugars (like maltose and glucose). These sugars are then fermented by yeast to produce alcohol and carbon dioxide. Pectinase is used in fruit juice production to break down pectin, clarifying the juice and increasing yield.
3. Dairy Industry: Lactase enzyme is used to hydrolyze lactose (milk sugar) into glucose and galactose. This process produces lactose-free milk products, making them digestible for individuals with lactose intolerance. Rennet, containing the enzyme chymosin, is used in cheese making to coagulate milk proteins.
4. Textile Industry: Enzymes like cellulase are used in denim finishing to give a "stone-washed" look by partially degrading cellulose fibers, softening the fabric and removing surface fuzz. Amylases are used to remove starch-based sizing agents from fabrics after weaving, a process called desizing.

Question 4, Part 3:

A colloidal system is a heterogeneous mixture where one substance (the dispersed phase) is dispersed uniformly throughout another substance (the dispersion medium). The dispersed particles are larger than molecules in a true solution but small enough not to settle out like in a suspension, typically ranging from $1 \text{ nm}$ to $1000 \text{ nm}$ in diameter.

• Particle Size:

  • True Solutions: Particle size is less than $1 \text{ nm}$ (e.g., ions, small molecules).
  • Colloidal Systems: Particle size ranges from $1 \text{ nm}$ to $1000 \text{ nm}$.
  • Suspensions: Particle size is greater than $1000 \text{ nm}$.

• Stability:

  • True Solutions: Extremely stable; particles do not settle out.
  • Colloidal Systems: Generally stable; particles do not settle under gravity but can be destabilized (e.g., by electrolytes) leading to coagulation.
  • Suspensions: Unstable; particles settle out over time due to gravity.

• Separation Behaviour:

  • True Solutions: Cannot be separated by filtration or centrifugation.
  • Colloidal Systems: Cannot be separated by ordinary filtration, but can be separated by ultracentrifugation or ultrafiltration.
  • Suspensions: Can be separated by simple filtration or by allowing particles to settle.

Question 4, Part 4:

Coagulation is the process where dispersed colloidal particles lose their stability, aggregate into larger masses, and then settle out of the dispersion. This process is often irreversible and typically occurs when the repulsive forces between particles are overcome, allowing attractive forces to dominate.

Flocculation is the process of forming loose, open aggregates (flocs) of colloidal particles. These flocs are often larger and less dense than coagulated particles and can sometimes be redispersed. Flocculation is often induced by adding specific chemicals (flocculants) that bridge particles together.

The primary difference lies in the nature of the aggregates and their reversibility. Coagulation typically results in dense, compact aggregates that are difficult to redisperse, leading to irreversible settling. Flocculation, on the other hand, forms looser, more open aggregates that may be more easily redispersed, making it a potentially reversible process. Coagulation often involves a complete loss of colloidal stability, while flocculation can be a controlled aggregation process.

Question 4, Part 5:

Colloidal particles are normally stable in dispersion due to two main factors:

1. Surface Charge: Most colloidal particles acquire an electrical charge on their surface, often due to the adsorption of ions from the dispersion medium. Since all particles of a given colloid typically carry the same type of charge (e.g., all positive or all negative), they repel each other. This electrostatic repulsion prevents the particles from coming close enough to aggregate and settle.
2. Solvation Layer: Many colloidal particles are surrounded by a layer of solvent molecules (a solvation layer). This layer acts as a physical barrier, preventing direct contact between particles and hindering their aggregation. For hydrophilic colloids, this layer of water molecules is particularly strong, contributing significantly to their stability.