Enzymes - Biology Blitz | FULLY Explained in One Video | Leaving Cert Biology

The session introduces the three-week Biology Blitz, a 30-hour revision program covering 30-40% of the Leaving Cert syllabus. The first week, which is free, focuses on seven key chapters: Enzymes, Respiration, Cell Division, Photosynthesis, Cell Structure, Cell Diversity, and Osmosis Diffusion. Enzymes are covered first, as they are a high-value chapter, appearing almost every year and often contributing a significant percentage to the overall paper.

An enzyme is defined as a biological catalyst, a protein that speeds up chemical reactions without being consumed. Enzymes are synthesized in ribosomes and have a folded, specific shape. They are categorized as either catabolic (breaking down larger molecules, e.g., amylase, lipase, protease in digestion) or anabolic (building up smaller molecules, e.g., DNA polymerase in DNA synthesis). Important reactions controlled by enzymes include respiration, photosynthesis, and protein synthesis.

Temperature and pH are crucial factors influencing enzyme activity. Human enzymes generally have an optimum temperature of 37°C, while plant enzymes prefer 20-30°C. As temperature increases, enzyme activity rises until it reaches the optimum, then decreases sharply due to denaturation. Denaturation means the enzyme loses its specific shape and function. Similarly, enzymes have an optimum pH, with activity decreasing at extreme pH values (either very high or very low). It's important to distinguish between 'temperature' (a factor affecting activity) and 'extreme heat' (a factor causing denaturation).

The active site theory explains how enzymes work. The active site, a specific region on the enzyme, changes shape to precisely fit a particular substrate. This forms an enzyme-substrate complex, leading to the conversion of the substrate into products. After the reaction, the enzyme's active site returns to its original shape and can be reused, highlighting its role as a catalyst.

Three key experiments involving the enzyme catalase, substrate hydrogen peroxide, and products water and oxygen are discussed. These experiments investigate the effect of pH, temperature, and heat denaturation on catalase activity, measured by the volume of foam produced (oxygen trapped by washing-up liquid). The procedures are largely similar, varying only in the factor being manipulated (pH buffers for pH, different temperature water baths for temperature) and the factors being kept constant.

This experiment focuses on denaturing catalase by boiling celery (the source of catalase). The boiled catalase is then compared to unboiled catalase. In this case, both temperature and pH are kept constant during the reaction, but the initial boiling step denatures the enzyme, leading to no foam production in the test (denatured enzyme) compared to the control (undenatured enzyme), where foam is produced.

Immobilized enzymes are enzymes attached to each other or trapped in an inert material like a gel (e.g., sodium alginate). This technique is crucial in bioprocessing, where enzymes are used in bioreactors to produce products (like vitamins or antibiotics). The main advantages of immobilization are that the enzyme can be easily removed from the product, leading to a purer product, and the enzyme can be reused, making industrial processes more cost-effective. An example is using immobilized sucrase to break down sucrose into glucose and fructose, which are used as sweeteners.

This two-part experiment demonstrates enzyme immobilization and its application. Part one involves preparing immobilized enzymes by mixing yeast (containing sucrase) with sodium alginate and then adding this mixture dropwise into a calcium chloride solution. The calcium chloride hardens the alginate beads, trapping the yeast (and thus the sucrase) within. Rinsing then removes any untrapped enzymes. Part two examines the application: immobilized sucrase beads are placed in a funnel, and sucrose solution is passed through. The product (glucose and fructose) is collected and tested for glucose using test strips. A non-immobilized yeast control shows a cloudy product due to the presence of yeast in the final solution, while the immobilized enzyme yields a clear, purer product.