Key concepts in biology study guide

Enzymes are biological catalysts, typically proteins, that speed up the rate of biochemical reactions within living organisms without being consumed in the process. Their specific function relies on a unique three-dimensional structure, particularly the active site — a region designed to bind specifically with a reactant molecule, known as the substrate. This binding is often described by the 'lock and key' hypothesis, where the active site (the lock) has a complementary shape to the substrate (the key). Optimal conditions, such as temperature and pH, are crucial for maintaining this specific shape. However, if these conditions deviate significantly from the optimum, the enzyme's structure can be altered. For instance, extreme temperatures can cause the vibrations of the enzyme molecule to increase dramatically, breaking the weak bonds that maintain its tertiary structure. Similarly, significant changes in pH can alter the charges of the amino acids within the enzyme, disrupting ionic and hydrogen bonds. This alteration of the enzyme's three-dimensional structure, especially the active site, is known as denaturation. When denatured, the active site changes shape, meaning it can no longer bind effectively to its specific substrate. Consequently, the enzyme loses its catalytic activity, and the reaction it was supposed to catalyse slows down or stops entirely. Denaturation is often irreversible, permanent damage to the enzyme.

Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution). When studying osmosis in living tissues, such as potato cylinders, we often measure changes in mass. If the tissue gains mass, it has absorbed water via osmosis. If it loses mass, it has lost water. To quantify these changes, we calculate the percentage change in mass. This involves finding the difference between the final and initial masses, dividing by the initial mass, and then multiplying by 100. This percentage allows for a standardised comparison between experiments, regardless of the initial mass of the sample.