The course of an enzyme-controlled reaction

• how can you follow the progress of an enzyme-catalysed reaction for a given concentration of substrate?

  by measuring either the formation of product or the disappearance of substrate
• what happens when the enzyme and substrate are first mixed together? (the formation of a product over time) (step 1)

  there are many substrate molecules
• what happens to the enzyme and substrate molecules? (the formation of a product over time) (step 2)

  they are in constant motion and collide
• what do substrate molecules bind to? (the formation of a product over time) (step 3)

  they bind to the active sites of the enzyme molecules
• what happens to the substrate in a successful collision? (the formation of a product over time) (step 4)

  • the substrate is broken down and products are released
  • more active sites are then filled with substrate molecules
• what does the rate of reaction initially depend on and what is the limiting factor? (the formation of a product over time) (step 5)

  • initially, the rate of reaction depends on the number of free active sites, if all other conditions are optimal and theres excess substrate
  • the enzyme concentration is the limiting factor because it controls the rate of reaction
• what happens as the reaction (the formation of a product over time) proceeds and what is its limiting factor? (step 6)

  • as the reaction proceeds, theres less substrate and more product
  • the enzyme concentration is constant
  • the substrate concentration is the limiting factor as it controls the rate of the reaction
• what happens to the reaction eventually? (the formation of a product over time) (step 7)

  the substrate has been used up and no more product can be formed so the line plateaus (in a graph)
• what happens to the line in the graph at the end? (the formation of a product over time) (step 8)

  the line goes through the origin, because at 0 time, no reaction has happened yet
• what does this graph show?

  the formation of a product formed over time