Explain enzyme specificity and the induced-fit model. Describe the effect of temperature on enzyme activity.

5. (a) (i)
Enzyme specificity refers to the ability of an enzyme to catalyze only one specific type of reaction or act on only one particular substrate or a very limited range of substrates. This is due to the unique three-dimensional shape of its active site, which is complementary to the shape of its specific substrate.

5. (a) (ii)
The induced-fit model proposes that the active site of an enzyme is not a rigid structure but is flexible. When a substrate binds to the active site, it induces a conformational change in the enzyme, causing the active site to mold precisely around the substrate. This induced fit brings the substrate into an optimal orientation for the reaction and strains the bonds within the substrate, making them easier to break or form. By straining bonds and bringing reactants into close proximity and correct orientation, the enzyme effectively lowers the activation energy required for the reaction to proceed, thereby speeding up the reaction rate.

5. (b) (i)
The curve showing enzyme activity versus temperature typically rises gradually, peaks at an optimum, and then drops sharply.

• Initial rise: As temperature increases from low levels, the kinetic energy of both enzyme and substrate molecules increases. This leads to more frequent and energetic collisions between the enzyme's active site and the substrate, increasing the rate of enzyme-substrate complex formation and thus the reaction rate.
• Optimum temperature (37 °C): This is the temperature at which the enzyme exhibits its maximum activity. At this point, the enzyme's structure is stable, and the kinetic energy is optimal for efficient catalysis.
• Sharp drop above 45 °C: Beyond the optimum temperature, the increased kinetic energy causes excessive vibrations within the enzyme molecule. This disrupts the weak bonds (e.g., hydrogen bonds, ionic bonds) that maintain the enzyme's specific three-dimensional tertiary structure, particularly the precise shape of the active site. This irreversible change in shape is called denaturation. A denatured active site can no longer bind effectively to the substrate, leading to a rapid and permanent loss of enzyme activity.

5. (b) (ii)
A thermophilic bacterium isolated from a hot spring would have enzymes, including catalase, that show a higher optimum temperature because these organisms are adapted to survive and thrive in extremely hot environments. Their enzymes have evolved to possess a more stable and rigid tertiary structure with a greater number of strong intramolecular bonds (e.g., disulfide bridges, hydrophobic interactions) or more compact folding. This enhanced structural stability allows their active sites to maintain their functional shape and catalytic activity at much higher temperatures, resisting denaturation that would occur in enzymes from mesophilic organisms (like human liver catalase) at those temperatures.

5. (c)
Enzyme immobilisation is the technique of restricting enzyme movement by confining it to an insoluble matrix or support material, while still allowing its catalytic activity. This can be achieved through methods such as adsorption, covalent bonding, entrapment, or cross-linking.

Importance in the food industry:

1. Reusability: Immobilized enzymes can be easily recovered from the reaction mixture and reused multiple times, significantly reducing production costs.
2. Increased stability: Immobilization often enhances the enzyme's stability against changes in temperature, pH, and proteolysis, allowing for broader operating conditions and longer shelf-life.
3. Continuous processes: Immobilized enzymes facilitate continuous flow processes in bioreactors, leading to higher productivity and easier automation compared to batch processes with free enzymes.
4. Product purity: The enzyme does not contaminate the final product, simplifying downstream processing and purification steps, which is crucial for food safety and quality.

Cameroon-relevant example:
In Cameroon, a relevant example is the use of immobilized lactase in the dairy industry. Lactase is used to hydrolyze lactose in milk into glucose and galactose, producing lactose-free milk and dairy products. This is important for individuals with lactose intolerance, a common condition globally and in many African populations, including Cameroon. Immobilized lactase allows for efficient, continuous production of lactose-free milk, making dairy products accessible to a wider consumer base without causing digestive discomfort.