Enzyme Catalysis & Regulation

What is a prosthetic group?

A coenzyme that is tightly bound to an enzyme.

What are enzymes?

Globular proteins with a specific 3D shape that act as biological catalysts to speed up chemical reactions without being consumed.

Why are enzymes important?

They direct all metabolic events and maintain normal function in the body.

How do enzymes act as catalysts?

They lower the activation energy of a chemical reaction using a specific active site.

What is the active site?

A specific, precisely shaped pocket on an enzyme that binds substrates via geometric and electrostatic complementarity.

What is an enzyme-substrate (ES) complex?

The temporary complex formed when an enzyme binds its substrate in the active site.

What is the transition state?

A high-energy intermediate state forced by the active site to promote bond changes in the substrate.

What are Transferases?

Enzymes that transfer chemical groups such as phosphate, nitrogen, or carbon.

What are Ligases?

Enzymes that form new bonds.

How are enzymes used as diagnostics?

Elevated serum enzyme activities (e.g., GGT, creatine kinase) help detect tissue damage, monitor disease progression, and assess organ health.

How are enzymes used as therapeutic agents?

They can be targeted by drugs, such as statins which inhibit the enzyme that produces cholesterol.

What are the five factors that regulate enzyme activity?

- Temperature

- pH

- Substrate concentration

- Cofactors/coenzymes

- Enzyme inhibition.

How does temperature affect enzyme activity?

Velocity increases up to an optimum (35-40°C in the body) before decreasing due to irreversible denaturation.

What is enzyme denaturation?

The structural breakdown of an enzyme that disrupts its active site and function.

How does pH affect enzymes?

Changes affect amino acid side-chains within the active site and can cause denaturation; each enzyme has an optimum pH.

What is Vmax in enzyme kinetics?

The maximum velocity reached when enzyme rate increases with substrate concentration.

What is the difference between Michaelis and allosteric enzymes?

Michaelis enzymes have a hyperbolic kinetic curve, while allosteric enzymes have multiple subunits/active sites and display a sigmoid curve.

What is the difference between cofactors and coenzymes?

Cofactors are inorganic metal ions (e.g., Mg²⁺, Zn²⁺), while coenzymes are organic molecules (e.g., vitamins).

What is the difference between an apoenzyme and a holoenzyme?

An apoenzyme is an inactive enzyme without its cofactor, while a holoenzyme is an active enzyme with its cofactor.

What is an irreversible enzyme inhibitor?

An inhibitor that binds to a site other than the active site and permanently prevents enzyme activity (e.g., aspirin).

What is a reversible enzyme inhibitor?

An inhibitor that binds to the active site, allowing for dissociation and recovery of enzyme activity.