Summary
Highlights
Enzymes are protein-based catalysts that accelerate chemical reactions by lowering activation energy. While most are protein-based, some RNA catalysts called ribozymes also exist. Enzymes are easily identified by the '-ase' suffix in their names, like sucrase.
Enzymes possess an active site with a specific 3D shape complementary to their substrate. The 'lock and key' model suggests a perfect fit, while the 'induced fit' model explains that the enzyme's shape adjusts slightly for an even better fit upon substrate binding. This forms an enzyme-substrate complex, which then releases products and the unchanged enzyme, allowing the enzyme to be reused.
Enzyme activity is influenced by pH and temperature. Most enzymes have an optimal pH between 6 and 8. Extremes in pH can denature enzymes, altering their shape and function. Similarly, enzymes have an optimal temperature; increasing temperature initially boosts activity, but excessively high temperatures lead to denaturation and a rapid decrease in function.
Increasing substrate or enzyme concentration initially increases reaction rate, but eventually, the rate plateaus due to saturation. Inhibitors, such as competitive inhibitors (binding to the active site) and non-competitive/allosteric inhibitors (binding elsewhere to change the active site's shape), decrease enzyme activity. Conversely, activators enhance enzyme activity. Some enzymes also require cofactors (inorganic metal ions) or coenzymes (organic molecules like vitamins).
Several enzyme types are named based on their function: protease breaks down proteins, lipase breaks down fats, isomerase catalyzes rearrangement reactions, transferase moves functional groups, kinase transfers phosphate groups (often from ATP), dehydrogenase removes hydrogen atoms, amylase breaks down starch, oxidoreductase catalyzes electron transfer in redox reactions, and hydrolase catalyzes hydrolysis reactions.