Enzymes and Metabolism

• Catabolism: The breakdown of compounds.
• Anabolism: The building of compounds.
• Metabolism: The sum of all enzyme reactions in a cell.
• Coenzyme: An organic molecule (not a protein) that might be required by an enzyme; many vitamins serve as coenzymes.
• Cofactor: An inorganic molecule that might be required by an enzyme (e.g., Fe+, Zn+, Ca+).
• Apoenzyme: The protein component of an enzyme, which may act on its own depending on the enzyme.
• Allosteric Site: An alternative site on an enzyme, away from the active site.
• Active Site: The specific region of an enzyme where substrates bind; its shape is essential for enzyme function.
• Dehydrogenation: The removal of a hydrogen atom and an electron from a molecule.

Oxidation and Reduction

• Oxidation: Loss of an electron.
• Reduction: Gain of an electron.

Enzyme Definition and Function

• Enzymes are catalysts, speeding up reactions by lowering activation energy without being permanently altered.
• Most enzymes are proteins.
• Enzymes accelerate metabolic reactions and lower the activation energy required for these reactions.

Enzyme Nomenclature

• Enzyme names typically end in "-ase."

Enzyme Expression/Production

• Constitutive Enzymes: Produced constantly; their activity remains unchanged.
• Inducible Enzymes: Production or activity increases in response to environmental signals.
• Repressible Enzymes: Production or activity decreases in response to environmental signals.

Enzyme Mechanism of Action

• Two substrates bind to the enzyme's active site, forming an enzyme-substrate complex.
• The substrate is then transformed into products.
• The products are released, and the enzyme is recycled to catalyze additional reactions.

Factors Influencing Enzyme Activity

• Temperature:
  • Low temperatures slow molecular movement and can make the enzyme rigid.
  • High temperatures can denature the protein, breaking bonds and causing it to unfold.
• pH:
  • Extreme pH levels can cause enzymes to denature.
  • Enzymes have an optimal pH range for activity.
• Substrate Concentration:
  • Saturation occurs when all active sites are filled with substrate.
  • Once saturation is reached, increasing substrate concentration will not increase enzyme activity.
• Inhibitors:
  • Competitive Inhibitors: Bind to the active site, preventing substrate binding; can be reversible or irreversible. An example is the antimicrobial agent sulfanilamide.
  • Noncompetitive Inhibitors: Bind to an allosteric site, changing the shape of the active site and preventing substrate binding; can be reversible or irreversible. Feedback inhibition is a form of noncompetitive inhibition that prevents the cell from wasting resources.

Competitive vs. Noncompetitive Inhibitors

• Both types of inhibitors prevent enzymes from producing products.

Competitive Inhibitors:

• Bind to the active site.
• Can be reversible or irreversible.
• Do not change the enzyme's shape.
• Example: Sulfanilamide.

Noncompetitive Inhibitors:

• Bind to the allosteric site.
• Can be reversible or irreversible.
• Change the shape of the active site.
• Utilize feedback inhibition to inhibit the first enzyme in a metabolic pathway.

Feedback Inhibition

• The end product of a series of reactions inhibits the first enzyme in the series.
• This mechanism prevents the cell from wasting resources

Metabolic Pathway Concepts

• In a hypothetical pathway A → B → C ↔ D → E:
  • A is the initial substrate, and B is the first product.
  • Curved lines indicate coupled reactions.
  • The reaction between C and D is reversible.
  • Inputs such as O2 (reactants) and byproducts such as CO2 and H2O may be involved.
  • E is the main end product.
  • B, C, and D are intermediate products.

Oxidation/Reduction Reactions

• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.
• These reactions are often coupled, with one molecule being oxidized while another is reduced.