Exam 2: Enzyme regulation

1. What is feedback inhibition?

• The end product of a pathway inhibits an enzyme near the beginning.

• Prevents wasting energy and resources

2. What is allosteric regulation?

• A regulator binds at a site different from the active site.

• Changes the enzyme's shape and activity.

3. What is positive allosteric regulation?

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• Regulator binds and makes the enzyme more effective.

• Increases reaction rate.

4. What is negative allosteric regulation?

• Regulator binds and makes the enzyme less effective.

• Decreases reaction rate.

5. What is reversible inhibition?

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• Inhibitor binds temporarily.

• Enzyme activity returns when the inhibitor leaves.

• What is irreversible inhibition?

• Inhibitor permanently inactivates the enzyme.

• Activity cannot be restored simply by removing free inhibitor

• Enzyme is permanently disabled.

What is competitive inhibition?

• Inhibitor resembles the substrate and binds the active site.

• Competes with the substrate for binding.

• Can be overcome by increasing substrate concentration.

8. What is noncompetitive inhibition?

• Inhibitor binds away from the active site.

• Reduces enzyme activity by interfering with catalysis.

• Cannot be overcome by adding more substrate.

9. How do competitive inhibitors affect Vmax?

vmax same

9. How do noncompetitive inhibitors affect Vmax?

vmax decreases

How can you identify competitive vs. noncompetitive inhibition on a graph?

• Competitive: Both curves eventually reach the same maximum rate.

• Noncompetitive: The inhibited enzyme reaches a lower maximum rate.

11. How do statins work?

• Act as competitive inhibitors.

• Bind to the active site of HMG-CoA reductase.

• Reduce cholesterol synthesis.

How does aspirin inhibit enzymes?

• Irreversibly inhibits cyclooxygenase (COX).

• Adds an acetyl group to a serine residue.

• Reduces prostaglandin production.

13. What are prostaglandins?

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• Short-lived signaling molecules made from fatty acids.

• Help regulate inflammation.

14. Why can aspirin cause stomach irritation?

• Reduces prostaglandin production.

• Decreases protection against stomach acid.

5. What is the difference between COX-1 and COX-2 in your lecture?

• COX-1: Associated with thromboxane production and platelet clumping.

• COX-2: Associated with prostacyclin production, which reduces platelet clumping.

What is a zymogen (proenzyme)?

• An enzyme produced in an inactive form.

• Activated by cleavage of part of the protein.

• Example: Digestive enzymes and blood-clotting enzymes.

Why are zymogens important?

• Prevent enzymes from acting too early.

• Allow activation only when and where needed.

What is covalent modification?

• Adding or removing a chemical group from an enzyme.

• Changes enzyme activity..

• What is phosphorylation?

• Addition of a phosphate group to a protein.

• Can activate or inhibit enzyme activity.

What is the difference between kinases and phosphatases?

• Kinase: Adds phosphate from ATP.

• Phosphatase: Removes phosphate

. What is genetic control of enzymes?

• Controls how much enzyme is produced.

• Example: E. coli produces β-galactosidase when lactose is present.

. What is a coenzyme?

• A small organic molecule that helps enzymes catalyze reactions.

• Often derived from vitamins.

What is the difference between fat-soluble and water-soluble vitamins?

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• Fat-soluble: A, D, E, K; can be stored in body fat.

• Water-soluble: B vitamins and C; many B vitamins form coenzymes.

What are NAD⁺ and NADH?

• NAD⁺: Oxidized form; accepts electrons.

• NADH: Reduced form; carries stored reducing power.

• Derived from vitamin B₃ (niacin).

What is FAD/FADH₂?

• Electron-carrying coenzyme used in redox reactions.

• Derived from vitamin B₂ (riboflavin).

Types of inhibition

reversible

irreversible

completive

noncompetitive

allosteric

Methods of enzyme regulation

-zymogen

-covalent modification

-phosphorylation

-genetic control