Enzyme Function and Mechanism

Overview of Enzymes

• Enzymes are essential for speeding up chemical reactions in cells.

• Activation energy is the minimum energy required for reactants to transform into products.

• Reactions can be exergonic (releasing energy) or endergonic (requiring energy).

Enzyme Function

• Enzymes lower activation energy to facilitate reactions without increasing temperature.

• They help reactants collide in the correct orientation in the active site, leading to the transition state.

Structure and Specificity

• Most enzymes are proteins, with some being RNA (ribozymes).

• Enzymes have active sites, where specific substrates bind; this binding can change the shape of the enzyme (induced fit model).

• Enzyme specificity is due to the shape and chemical properties of the active site.

Mechanism of Action

• Steps in enzyme-catalyzed reactions:

  1. Initiation: Enzymes align substrates for optimal collisions.

  2. Transition state facilitation: Enzymes help achieve the transition state by reducing the activation energy.

  3. Termination: Products are released, and the enzyme reverts to its original structure.

Factors Affecting Enzyme Activity

• Enzyme kinetics show reaction rates depending on substrate concentration.

• After a certain substrate concentration, enzyme activity levels off (saturation).

Enzyme Helpers

• Enzymes often require additional molecules:

  • Cofactors: Inorganic ions (e.g., Zn²⁺, Mg²⁺).

  • Coenzymes: Organic molecules (e.g., NADH, FADH₂).

  • Prosthetic groups: Permanently attached non-protein molecules.

Importance of Vitamins

• Many vitamins function as coenzymes; deficiencies can lead to enzyme dysfunction and diseases, e.g., vitamin C is vital for collagen synthesis.