Enzymes

• What are enzymes?


  Biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves
• What is an advantage of enzymes in the body?

  They enable cellular reactions to take place at lower temperatures
• What is the active site of an enzyme?

  The region of an enzyme to which a substrate molecule binds and the reaction takes place
• Why are enzymes described as having a ‘high specificity’ for their substrate?

  Only substrates with a specific, complimentary shape can fit into an enzymes active site
• Describe the ’lock and key’ model

  1. Substrate collides with the active site of an enzyme
  2. Substrate binds, enzyme-substrate complex forms
  3. Substrate converted to products
  4. Products released from the active site which is now free to bind to another substrate
• What factors affect the rate of an enzyme controlled reaction?

  • Temperature

  • pH

  • Substrate concentration
• Explain how increasing temperature initially affects the rate of an enzyme-controlled reaction

  • As temperature increases, molecules have more kinetic energy

  • Movement of molecules increases

  • Probability of a successful collision increases

  • More enzyme-substrate complexes form

  • Rate of reaction increases
• Explain how increasing temperatures above the optimum affects the rate of an enzyme-controlled reaction

  • Temperature increases above the optimum

  • Increases vibrations break bonds in enzyme’s structure

  • Active site changes shape, enzyme is denatured

  • No more enzyme-substrate complexes can form

  • Rate of reaction decreases
• Explain how pH affects the rate of an enzyme-controlled reaction

  • Enzymes have an optimum pH

  • pH shifts from the optimum

  • Bonds in the enzyme’s structure are altered

  • Active site changes shape, enzyme is denatured

  • Rare of reaction decreases
• Explain how the substrate- concentration affects the rate of an enzyme-controlled reaction

  • Substrate concentration increases

  • Number of substrate molecules in the same volume increases

  • Probability of a successful collision increases

  • More enzyme-substrate complexes form

  • Rate of reaction increases

  • Once all active sites become full, the rate of reaction plateaus
• How can the rate of an enzyme-controlled reaction be calculated when given a value for time?

  Rate = 1/time
• What are the units for rate?

  S$^-1$
• Why must large organic molecules be broken down into smaller, simpler units in the body?

  • Large molecules are too big to be absorbed across the surface of the gut wall

  • Large molecules are broken down into smaller molecules for absorption into the bloodstream
• Give an example of the breakdown of large molecules into smaller molecules in plants

  Starch is broken down by enzymes into simpler sugars which are respired to release energy
• What type of molecule are proteins and carbohydrates?

  Polymers
• What are the monomers of carbohydrates?

  Simple sugars
• Which group of enzymes catalyses the breakdown of carbohydrates?

  Carbohydrases
• Which type of carbohydrase catalyses the breakdown of starch?

  Amylase
• What are the monomers of proteins?

  Amino acids
• Which type of enzyme catalyses the breakdown of proteins?

  Protease
• Function of lipases


  Enzymes which catalyse the breakdown of lipids into fatty acids and glycerol
• Why are small molecules synthesised into larger organic molecules in the body?

  • Large molecules are used for storage (e.g. glycogen)

  • Large molecules are used to build structures (e.g. organelles)
• Which enzyme catalyses the formation of glycogen from glucose?

  Glycogen synthase