Enzymes: Controlling Reactions in the Cell

Enzymes: Controlling Reactions in the Cell

• Chemical reactions in a cell are called metabolic reactions
• Metabolic reactions are controlled by enzymes
• Enzymes are proteins that act as biological catalysts
• Catalysts speed up reactions without being used up
• Enzymes take part in reactions, but are not changed afterwards
• Cells contain many different enzymes, each for a specific reaction
• Enzymes' function is to catalyse metabolic reactions
• Enzyme activity is controlled by genes in the nucleus
• Organisms maintain a relatively stable internal temperature (e.g., 37°C in humans) which speeds up reactions by using enzymes

Factors Affecting Enzymes

• Temperature:
  • Optimum temperature is the best temperature for a reaction
  • Higher temperatures increase kinetic energy, increasing collisions between molecules leading to a faster reaction
  • However, too high temperatures can denature enzymes (causing a loss of shape and function).
• Substrate Concentration:
  • Increasing substrate concentration increases the rate of reaction up to a certain point.
• Enzyme Concentration:
  • Increasing enzyme concentration increases the rate of reaction proportionally, up to a certain point.
• pH:
  • Enzymes have optimal pH ranges
  • Extreme pH values can denature enzymes.

How Enzymes Work

• Enzymes have an active site
• The substrate molecule attaches to the enzyme's active site
• The reaction takes place which converts substrate into products
• The products leave the active site
• Enzymes fit into substrate molecules like a lock and key
• This makes enzymes specific (they only work on specific substrates)