enzymes

Question 1

describe the lock and key model

Answer 1

substrate binds to the active site for the enzyme to facilitate the reaction.
a substrate will only fit the active site of one specific enzyme.

Question 2

describe the induced fit model

Answer 2

• substrate binds to the active site of enzyme, causing active sit to change shape so its complementary.
• as it changes shape the enzyme puts a strain on the substrate.
• enzyme substrate complex forms.
• the strain distorts a particular bond, lowering the activation energy needed to break the bond.

Question 3

what are competitive inhibitors?

Answer 3

they are a type of enzyme inhibitor which bind directly to the active site to prevent the enzyme from working.

Question 4

what are non - competitive inhibitors?

Answer 4

they are a type of enzyme inhibitor which bind to an allosteric site, changing the shape of the active site so the substrate can no longer bond.

Question 5

what factors affect enzyme activity?

Answer 5

enzyme concentration
substrate concentration
concentration of inhibitor
temperature
pH

Question 6

how does temperature affect enzyme activity?

Answer 6

• if too low then there is not enough kinetic energy so the rate decreases.
• if increased then there is more kinetic energy so the rate increases.
• if too high then the enzymes denature so fewer enzyme substrate complexes form and the rate decreases.

Question 7

how does pH affect enzyme activity?

Answer 7

if too high/too low then enzymes denature so fewer enzyme substrate complexes form and rate decreases.

Question 8

how does the concentration of competitive inhibitors affect enzyme activity?

Answer 8

increasing it means there are fewer enzyme substrate complexes that can form, so the rate decreases.
this is because it’s a similar shape to the substrate so it binds to the active site so the substrate cant bind.

Question 9

how does substrate concentration affect enzyme activity?

Answer 9

increasing it means more enzyme substrate complexes form so the rate increases.
there are no empty active sites.

Question 10

how does enzyme concentration affect enzyme activity?

Answer 10

increasing it means more enzyme substrate complexes form so the rate increases.

Question 11

how do enzymes act as biological catalysts?

Answer 11

each enzyme lowers the activation energy of reaction it catalyses, to speed up the rate of reaction.

Question 12

explain the specificity of enzymes.

Answer 12

• specific tertiary structure determines shape of active site.
• active site is complementary to specific substrate.
• only this substrate can bind to active site, forming enzyme-substrate complex.

Question 13

how does the concentration of non-competitive inhibitors affect enzyme activity?

Answer 13

increasing it means there are fewer enzyme substrate complexes that can form, so the rate decreases.
this is because it binds to the allosteric site which changes the shape of active site so the substrate can no longer bond.

Question 14

describe how the rate of an
enzyme-controlled reaction can be measured.

Answer 14

• measure time taken for reaction to reach a set point.
• measure concentration/ volume/ mass at regular intervals.
• plot graph, draw tangent, rate of reaction.

Question 15

explain why the rate of reaction decreases over time throughout each experiment.

Answer 15

the initial rate is highest is highest as substrate concentration is not the limiting factor so many enzyme substrate complexes form.
reaction slows as substrate is used up and often stop as there is no substrate left.