Enzymes Notes

Definition of Enzymes: Enzymes are proteins that act as catalysts in chemical reactions, speeding up the reactions without being consumed or changed themselves.

Role of Enzymes in Chemical Reactions:
- Enzymes increase reaction rates by lowering the Activation Energy:
- Activation Energy: The minimum energy required to initiate a chemical reaction. Enzymes lower this energy barrier, facilitating the transition state necessary for the reaction to occur.

Substrate Binding:
- Enzymes are highly specific to their substrates—the molecules they act upon.
- The substrate(s) bind to the Active Site of the enzyme:
- Active Site: A specific region on the enzyme’s surface that has a shape and chemical properties complementary to the substrate(s).
Formation of Enzyme-Substrate Complex:
- ,Upon binding, the substrate forms an Enzyme-Substrate Complex, essential for the catalytic process.
Stabilizing Transition State:
- Transition State: An unstable, high-energy state that substrates must reach in order to form products.
Product Formation and Release:
- After the reaction, the enzyme releases the transformed substrate molecules as products. The enzyme remains unchanged and can catalyze further reactions.

Enzymes have high specificity for their substrates, undergoing conformational changes upon binding that enhance the interaction:
- This phenomenon is known as Induced Fit, where the binding of the substrate induces a change in the enzyme structure, optimizing the fit between enzyme and substrate.

Substrate Concentration:
- Enzymes with high affinity for their substrates can bind substrates efficiently even at low concentrations.
- The reaction rate, or velocity, is defined as the amount of product formed per second.
- The velocity increases with substrate concentration but eventually reaches a plateau.
- The plateau occurs because, at high substrate concentrations, all active sites on the enzyme are occupied. This saturation level represents the maximum rate of the reaction, also termed Vmax.

Definition of Inhibitors: Molecules that bind to enzymes and diminish their catalytic activity.
Types of Enzyme Inhibition:
1. Competitive Inhibition:
- An inhibitor binds to the active site of the enzyme, preventing the substrate from binding.
1. Non-Competitive Inhibition:
- An inhibitor binds to a secondary site, altering the enzyme's shape and preventing substrate binding.
- Can bind only to the enzyme-substrate complex, locking the substrate in place and halting product formation.
1. Uncompetitive Inhibition:
- Inhibitor binds to the enzyme-substrate complex, preventing the substrate from releasing products.
Examples of Inhibitors:
- Penicillin: Inhibits the enzyme responsible for bacterial cell wall synthesis (DD-transpeptidase).
- Aspirin: Acts as a non-competitive inhibitor of the enzyme cyclooxygenase (COX) involved in pain and inflammation. It stops the conversion of Arachidonic Acid into compounds like prostaglandins that mediate pain and inflammation.

Cofactors and Coenzymes:
- Enzymes may require non-protein molecules or ions for activity:
- Cofactors: Typically inorganic ions (e.g., Fe³⁺, Zn²⁺) that temporarily bind to enzymes to assist in reactions.
- Coenzymes: Organic molecules that bind temporarily to enzymes and participate in the reaction but are unchanged afterward.
- Prosthetic Groups: Small molecules permanently attached to enzymes, aiding in their function.

Temperature:
- The rate of reaction can vary significantly with temperature due to changes in kinetic energy. Extreme temperatures can denature enzymes, rendering them inactive.
pH Levels:
- Different enzymes have optimal pH levels for their activity. For example:
- Pepsin: A protease that digests proteins into peptides, functions optimally at a pH around 2.0, typical of gastric conditions.

The interaction of substrates with enzymes is complex and governed by various factors, including concentration, temperature, pH, and the presence of inhibitors.