Substrate concentration

• what does the rate of an enzyme-catalysed reaction vary with?

  with changes in substrate concentration
• what happens if the enzyme concentration is constant?

  the rate of reaction increases as the substrate concentration increases
• what happens at low substrate concentrations?

  the enzyme molecules have only a few substrate molecules to collide with so the active sites are not working to full capacity
• what happens with an increased amount of substrate?

  more active sites are filled
• why is concentration of substrate a limiting factor?

  as its controlling the rate of reaction
• what is a limiting factor?

  a factor that, when in short supply, limits the rate of reaction - an increase in the value of a limiting factor causes an increase in the rate of reaction
• what happens if even more substrate is added?

  at a critical concentration, all the active sites become occupied and rate of reaction is at its maximum
• how is the enzyme described when all the active sites are full?

  as saturated
• what is this a graph of?

  effect of substrate concentration on the rate of reaction

  
• what happens if even MORE substrate is added?

  reactions can’t be catalysed any faster so the line plateaus (on the graph)
• what does it mean when the line on the graph plateaus?

  it means that the reactions can’t be catalysed any faster and that the substrate concentration is no longer controlling the rate of reaction so its no longer a limiting factor - some other factor controls the rate of reaction (e.g. temperature)
• what does this diagram show?

  effect of low and high substrate concentration