Enzymes: Catalysts for Life

Key Concepts

• Enzymes: Proteins that catalyze chemical reactions in cells.
  • Initiate and speed up reactions.
  • Ensure consistent outcomes.
  • Work under mild conditions of pH, temperature, and pressure.
  • Make reactions millions to trillions of times faster than without catalysts.

Enzyme Functionality

• Enzymes catalyze reactions by:
  • Binding to substrates.
  • Holding substrates in optimal positions for reactions.
  • Stabilizing the transition state using reactive groups.

Citric Acid Cycle Example: Aconitase

• Aconitase: An enzyme in the Citric Acid Cycle.
  • Binds to citrate.
  • Converts citrate to isocitrate through intermediate cis-aconitate.
• Active Site Mechanics:
  • Involves amino acids such as Histidine 101 and Serine 642.
  • Iron-sulfur cluster assists in stabilizing and positioning substrates.

Reaction Steps

1. Dehydration:
   • Histidine protonates the hydroxyl group, releasing it as water.
   • Serine extracts a hydrogen atom, forming cis-aconitate.
2. Hydration:
   • Cis-aconitate flips.
   • Histidine adds a hydroxyl group from water.
   • Serine returns its hydrogen, releasing isocitrate.

Characteristics of Enzymes

• Catalysts that remain unchanged post-reaction.
• Active sites are often flexible, adapting to substrates.
• Can perform thousands of reactions successively.

Importance of Enzymes

• Essential for metabolism, protein synthesis, and cell growth/renewal.
• Fundamental to maintaining life processes across all living organisms.