Overview
This lecture covers two main examples of catalysis—catalytic converters in automobiles and enzyme activity in biological systems—demonstrating how catalysts stabilize reactive intermediates and accelerate reactions.
Catalytic Converters in Automobiles
- Catalytic converters use catalysts to convert harmful pollutants, such as nitrogen monoxide and carbon monoxide, into less toxic substances.
- Common pollutants are converted to nitrogen gas and carbon dioxide through catalytic reactions.
- Incomplete combustion in engines leads to unburnt fuel fragments, contributing to pollution.
- Platinum, palladium, and rhodium are used as catalysts due to their stability and low reactivity, classified as noble metals.
- Oxygen atoms can sit stabilized on platinum surfaces until they react with other atoms, reducing the formation of harmful compounds.
- These metals stabilize reactive intermediates without forming true chemical bonds, allowing cleaner emissions.
Enzyme Catalysis in Biological Systems
- Enzymes are proteins that catalyze biochemical reactions, increasing reaction rates in living organisms.
- Enzyme function involves substrate binding to the enzyme's active site, forming an enzyme-substrate complex.
- Binding occurs primarily via intermolecular forces rather than true covalent bonds.
- Two models explain enzyme-substrate interaction: the lock-and-key model (perfect fit) and the induced fit model (enzyme changes shape for fit).
- Example: Sucrose is hydrolyzed into glucose and fructose by the enzyme sucrase, which stabilizes the transition state and enables water to break the glycosidic bond.
- Hydrolysis reactions would not occur efficiently in solution without enzymes, as reactant bonds are too stable.
Key Terms & Definitions
- Catalyst — a substance that increases the rate of a chemical reaction without being consumed in the process.
- Catalytic converter — a device in automobiles that uses catalysts to convert pollutants into less harmful chemicals.
- Noble metals — metals like platinum, palladium, and rhodium that are chemically stable and found in pure form in nature.
- Enzyme — a biological protein catalyst that accelerates biochemical reactions.
- Active site — the specific region on an enzyme where the substrate binds and the reaction occurs.
- Lock-and-key model — explains enzyme specificity by a perfect fit between enzyme and substrate.
- Induced fit model — the enzyme and substrate adjust shapes to bind effectively.
- Hydrolysis reaction — a reaction where water breaks chemical bonds, such as in the breakdown of sucrose by sucrase.
Action Items / Next Steps
- Review textbook examples of catalysis, focusing on catalytic converters and enzymes.
- Study enzyme mechanisms and the differences between lock-and-key and induced fit models.
- Complete assigned reading on enzyme-catalyzed hydrolysis reactions.