enzymes : the effect of substrate concentration on the rate of enzyme-catalysed reactions

Question 1

define concentration

Answer 1

number of molecules per unit volume

Question 2

what happens if there isn’t any substrate present ?

Answer 2

• an enzyme-catalysed reaction can’t proceed

Question 3

why can’t the enzyme-catalysed reaction proceed ?

Answer 3

• as there aren’t any substrate molecules to fit into the enzyme molecules’ active sites
  –> so enzyme-substrate-complexes can’t be formed

Question 4

what happens when a substrate is added ?

Answer 4

• its concentration increases
  –> the rate of reaction also increases

Question 5

why does this occur and what does it lead to ?

Answer 5

• this is because more (ESC) can form
• more product molecules are formed

Question 6

what is the limiting factor and why ?

Answer 6

• substrate concentration is limiting the reaction –> as it increases –> the rate of reaction also increases

Question 7

what happens when the concentration of the substrate is increased further ?

Answer 7

• the reaction will reach its maximum rate

Question 8

what happens if one adds more substrate molecules after maximum rate and why ?

Answer 8

• it won’t increase the rate of reaction
• as all the enzymes active sites are occupied with substrate molecules
• if more substrate molecules are added they can’t successfully collide with and fit into an enzyme’s active site

Question 9

draw a graph representing the effect of increasing substrate concentration on the rate of an enzyme-controlled reaction and LABEL

Answer 9

find in textbook :)

Question 10

what is the balanced equation for the reaction controlled by catalase ?

Answer 10

H2O2 –> H2O + O2

Question 11

is catalase an intracellular enzyme or an extra cellular enzyme ?

Answer 11

intracellular

Question 12

draw an label the set up of the experiment

Answer 12

• conical flask with catalase source and hydrogen peroxide
• delivery tube
• measuring cylinder
• water trough

Question 13

explain the shape of the graph using biological ideas and relevant enzyme theory

Answer 13

• graph should show an increase in rate of gas production with an increase in substrate concentration
  –> this is because there is more substrate for the enzyme to work on so more product is formed more quickly
  –> if there is a levelling off , this is because the enzyme cannot work more quickly and the substrate molecules effectively have to queue up for an enzyme to become free
  –> so the rate levels off

Question 14

state a limitation of the experiment and how one could overcome it

Answer 14

• gas may escape while trying to put the bung in
  –> use a gas syringe or do replicates at each concentration

Question 15

how to calculate the rate of reaction on a graph ?

Answer 15

• construct a tangent line using a ruler
• calculate the gradient of the line by dividing change in y / change in x
• value is the initial rate of reaction