Overview
This lecture explains how enzymes lower activation energy, different mechanisms of enzyme regulation, and the importance of cofactors, coenzymes, and feedback inhibition.
How Enzymes Work
- Enzymes lower activation energy by helping substrates reach the transition state.
- They position substrates, create optimal environments, or stress substrates to make them more reactive.
- The active site contains specific amino acids that facilitate substrate binding and catalysis.
- Enzymes are unchanged by the reaction and can catalyze multiple rounds.
Factors Affecting Enzyme Activity
- Protein shape, determined by amino acid sequence, is essential for enzyme function.
- High temperatures can denature proteins, altering enzyme activity.
- pH changes can change the charge or shape of the active site, affecting binding.
Enzyme Regulation
- Enzyme activity is regulated by temperature, pH, compartmentalization in the cell, and availability of cofactors/coenzymes.
- Competitive inhibitors compete with substrates for the active site, slowing reaction rates.
- Non-competitive (allosteric) inhibitors bind to a different site (allosteric site), changing enzyme shape and preventing substrate binding.
- Allosteric activators bind to the allosteric site and promote enzyme activity by optimizing the active site.
Cofactors and Coenzymes
- Cofactors are inorganic ions (e.g., metals) required for enzyme activity.
- Coenzymes are organic molecules or vitamins that assist enzymes.
- Lack of essential coenzymes (e.g., vitamin C) can cause diseases like scurvy due to enzyme malfunction.
Feedback Inhibition
- Feedback inhibition occurs when the end product of a metabolic pathway acts as an allosteric inhibitor of an earlier enzyme.
- This method self-regulates product formation and conserves cellular energy.
- Example: Isoleucine acts as an allosteric inhibitor to stop its own synthesis when abundant.
Key Terms & Definitions
- Active site — region on enzyme where substrate binds and reaction occurs.
- Competitive inhibitor — molecule that competes with substrate for the active site.
- Non-competitive inhibitor — molecule that binds outside the active site, causing allosteric inhibition.
- Allosteric site — site on enzyme separate from the active site where regulators bind.
- Cofactor — inorganic ion required for enzyme function.
- Coenzyme — organic molecule or vitamin aiding enzyme action.
- Feedback inhibition — process where the end product shuts down its own production via allosteric inhibition.
Action Items / Next Steps
- Watch the linked video in the PDF slides for a 3D view of enzyme action.
- Prepare for Chapter 7 on cellular respiration.