factors affecting the rate of enzymic reactions

Question 1

what are the three factors that effect rate of enzymic reaction?

Answer 1

effect of substrate concentration

effect of temperature

effect of pH

Question 2

describe the graph of the effect of substrate concentration on rate of reaction (5)

Answer 2

for a given concentration of enzyme increasing the substrate concentration will increase the rate of reaction to a particular point at which the rate reaches a constant maximum rate (Vmax)

• the rate of reaction initially increases as collisions between substrate and enzyme molecules are more likely
• the rate of reaction then levels out as the active site of all the enzyme molecules are taken up by substrate molecules
• the rate of reaction is now limited by the time required for the enzyme/substrate complex to form the product and release it from the active site. the active sites are all occupied or said to be saturated.
• the only method of increasing the rate of reaction at these higher substrate concentrations is by the addition of more enzyme

Question 3

draw the graph of how increasing substrate concentration effects rate of reaction

Answer 3

see graph

Question 4

describe the graph of the effect of temperature on rate of reaction (6)

Answer 4

enzymes are less efficient at low temperatures as the rate of a reaction is slowed down by the reduced kinetic energy of the reactant molecules

• an increase in temperature provides the molecules with more kinetic energy resulting in more collisions between the active sites of enzymes and substrate molecules and therefore more enzyme-substrate complexes are formed
• this increases the rate of reaction up to the optimum temperature where the rate of reaction is at a maximum
• increasing the temperature above this causes the tertiary structure of the enzyme to denature as hydrogen and ionic bonds are broken
• the rate of reaction decreases as the substrate has difficulty binding to the altered active site (less enzyme-substrate complexes form)
• denaturation of proteins at temperatures above 50 degrees celsius is usually permanent as the tertiary structure is irreversibly altered and the substrate cannot bind to the active site

Question 5

draw the graph of how increasing temperature effects rate of reaction

Answer 5

see graph

Question 6

describe the graph for each temperature

Answer 6

see graph

at 25°C (line C) there is low kinetic energy, so the reaction proceeds at a slow rate due to fewer collisions between enzyme and substrate molecules. eventually all the substrate will be converted into product.

• at 37°C (line B) there is more kinetic energy, therefore the reaction proceeds at a faster rate due more frequent collisions between enzyme and substrate molecules. all substrate is converted into product.
• at 60°C (line A) there is a very high level of kinetic energy the reaction proceeds at a very fast rate due to many collisions between enzyme and substrate molecules. however, due to the very high kinetic energy hydrogen bonds begin to break, the enzyme begins to denature, so that eventually substrate molecules can no longer bind to the altered active site. the reaction stops before all the substrate is converted into product.

Question 7

describe the graph of the effect of pH on rate of reaction (6)

Answer 7

enzymes possess an optimum pH at which the rate of reaction is at a maximum

• most enzymes are active over a narrow pH range
• very different pH’s from the optimum can cause denaturation.
• the change in pH alters the ionic charges of acidic and basic groups
• hydrogen and ionic bonds are broken altering the tertiary structure and active site
• the substrate cannot bind to the altered active site

Question 8

draw the graph of how increasing pH effects rate of reaction

Answer 8

see graph