Overview
This lecture covers enzymes, including their types, properties, how they function in biological reactions, and the factors that affect their activity, such as pH and temperature.
Types of Enzymes
- Enzymes are categorized as extracellular (function outside the cell) and intracellular (function inside the cell).
- Extracellular enzymes, like salivary amylase, are secreted out of the cell via vesicles.
- Intracellular enzymes remain within the cell and are involved in processes such as food digestion in single-celled organisms or cell death via lysosomes.
Properties of Enzymes
- Enzymes are globular (three-dimensional, blob-shaped) proteins.
- Enzymes are reusable and required in small amounts.
- Each enzyme is substrate specific: its shape matches only a particular substrate.
- Enzymes are sensitive to pH and temperature, which can affect their activity.
Enzyme Action & Mechanism
- Enzymes act as catalysts, speeding up chemical reactions in cells.
- The substrate binds to the enzyme's active site, which fits its shape (lock and key model).
- Activation energy is provided by the enzyme to start reactions: anabolic (building up) or catabolic (breaking down).
- After the reaction, the product(s) leave the active site, and the enzyme remains unchanged for reuse.
Factors Affecting Enzyme Activity
- Each enzyme has an optimum pH and temperature for maximum activity.
- Deviations from optimum pH in either direction denature enzymes, permanently changing their shape and function.
- Low temperatures do not denature enzymes but make them inactive; high temperatures denature them irreversibly.
Key Terms & Definitions
- Enzyme — a protein that catalyzes (speeds up) chemical reactions in cells.
- Extracellular enzyme — enzyme secreted outside the cell.
- Intracellular enzyme — enzyme that functions within the cell.
- Vesicle — small membrane-bound sac that transports substances in a cell.
- Lysosome — vesicle containing digestive enzymes, involved in breakdown and cell death.
- Globular protein — a compact, round-shaped protein.
- Substrate — the reactant on which an enzyme acts.
- Active site — region on the enzyme where the substrate binds.
- Catalyst — a substance that speeds up a chemical reaction.
- Anabolic reaction — reaction that builds up complex molecules.
- Catabolic reaction — reaction that breaks down complex molecules.
- Activation energy — energy required to start a reaction.
- Optimum — the best or most favorable condition for enzyme activity.
- Denature — permanent change in enzyme shape, leading to loss of function.
- Homeostasis — maintenance of stable internal conditions.
Action Items / Next Steps
- Review and memorize key enzyme properties and terminology for exams.
- Practice explaining enzyme action using the lock and key model.
- Prepare flashcards with definitions for all key terms.