Enzymes Flashcards
Structure of enzymes
- globular protein
What determins enzyme active site shape?
Primary structure determines tertiary structure which determines active site shape.
Explain, using one named example, the effect of a competitive inhibitor on enzyme activity
- Statins - binds to HMG-CoA reductase (catalyses a reaction in production of cholesterol)
- Competitive inhibitor has similar structure to substrate
- Therefore it fits/ is complementary to active site
- Substrate cannot bind as ibhibitor remains binded
- Substrate and inhibitor compete for active site
- Therefore higher substrate concentration can overcome inhibitions.
What model is used to explain how enzymes work?
Induced fit model
- Enzyme and substrate come together
- Active site’s shape changes, molding to fit with the substrate
- Amino acids bond with substrate
- Activation energy is lowered and reaction completed
How does Induced fit model (IF) compare to lock and key model (L&K)?
Similarities
- In both models substrates bind to active site
- In both models an enzyme-substrate complex forms
Differences
- Substrate fits exactly in active site in L&K whereas in IF it does not
- In L&K, active site does not change, but in IF it does
How do enzymes lower activation energy?
Weakening bonds in substrate
What is an enzyme inhibitor
Substance which slows the rate of enzyme controlled reaction by preventing substrate from binding to active site
How do competitive inhibitors work?
They are similar in shape to substrate, so they bind to active site and prevent access to substrate molecules
How does the concentration of substrate affect rate of reaction with competitive inhibitors?
Higher concentrations
- Rate of reaction increases because more substrate molecules can displace competitive inhibitors
- Enzyme-substrate complex more likely
Lower concentrations
- Rate of reaction is slower because it is less likely substrate will bind with enzyme
- competitive inhibitors cannot be displaced easily
How do non-competitive inhibitors work?
They bind with allosteric site to change the tertiary active site structure which prevents substrate from binding
How does the concentration of substrate affect rate of reaction with NON-competitive inhibitors?
Higher concentrations do not dislodge NC inhibitor, so change in rate of reaction can often be permanent
What is mechanism based inhibition?
Permanent stopping of an enzyme from working
Explain, using one named example, the effect of a NON-competitive inhibitor on enzyme activity
Penicillin - binds to transpeptidase (reforms broken bonds in bacteria cell wall to grow)
- Complementary / binds to allosteric site
- Changes the tertiary structure of active site
- So shape changes and substrate can no longer bond with active site
What is end product inhibition?
When there is too much of a product from a metabolic pathway, the product itself acts as a non-competitive inhibitor for the first reaction in the pathway, so the amount of product produced decreases.
What is a metabolic pathway?
Series of enzyme-controlled chemical reactions which start with substrate and end with a product.
What is an example of end product inhibition?
Isoleucine is the end product made from the substrate threorine, and it acts as a non competitive inhibitor when isoleucine levels are too high.
How do low temperatures affect enzyme activity?
Does NOT cause denaturation
- Lowers kinetic energy and lowers efficiency
