Enzymes

Question 1

How do enzymes increase the rate of a reaction?

Answer 1

• An enzyme lowers the activation energy of the reaction it catalyses.

Question 2

What do the properties of an enzyme relate to?

Answer 2

• Properties of enzyme relates to tertiary structure of its active site and ability to combine with other substrates to form an enzyme- substrate complex.

Question 3

What are enzymes?

Answer 3

• Enzymes are tertiary-structure proteins that catalyse reactions.

Question 4

Why is the shape of the active site unique and specific? What does this mean, in terms of what can bind to the active site?

Answer 4

• The active site is specific/ unique due to specific folding in tertairy structure of protein.
• Specific shape of active site means that enzymes only attach to substrates that are complementary in shape.

Question 5

What is activation energy (bio definition?)

Answer 5

• The certain amount of energy required before a reaction can occur.

Question 6

What are the two models for enzyme action called?

Answer 6

• Lock and key model.
• Induced fit model.

Question 7

Desribe the lock and key model.

4 key points

Answer 7

• Suggests enzyme active site is a fixed shape.
• Due to random collisions, only one type of substrate (with specific shape) can collide and attach to enzyme: forming enzyme- substrate complex.
• Charged groups in active site distort substrate (lowering activation energy.)
• Products are released/ enzyme can be re-used.

Question 8

Describe the induced- fit model.

3 key points

Answer 8

• Active site is induced to mould around a subtrate (ie. shape of active site isn’t exactly complementary to substrate.)
• Enzyme - substrate complex occurs –> active site moulding puts strain on the bonds (in substrate), lowering the activation energy.
• Products are released/ active site returns to original shape.

Question 9

True or False

Lock and key model is accepted model for enzyme function.

Answer 9

• False.
• Induced-fit model is the accepted model for enzyme function.

Question 10

Give 5 factors that affect the rate of enzyme-controlled reactions.

Answer 10

1.) Temp.
2.) pH
3.) Substrate concentration.
4.) Enzyme concentration.
5.) Inhibitors (competitive/ non-competitive.)

Question 11

If temperature is too low, how will this affect the rate of an enzyme- controlled reaction?

Answer 11

• Temperature = too low: substrate/ enzyme don’t have enough kinetic energy for successful collisions between enzyme (active site) and the substrate.
• So, fewer enzyme- substrate complexes are formed.
• So, rate of reaction decreases.

Question 12

If temperature is too high, how will this affect an enzyme- controlled reaction?

Answer 12

• Temp = too high (enzyme has too much kinetic energy so bonds in tertiary structure of the enzyme are going to break.)
• Enzyme/ active site becomes denatured.
• Active site changes shape/ enzyme- substrate complexes cannot form.
• Rate of reaction decreases/ stops.

Question 13

If pH is too high/ low, how will this affect the enzyme- controlled reaction?

Answer 13

• Too high/ too low pH will interfere with the charges in the amino acids in the active site (too high = too many OH- ions, too low = too many H+ ions.)
• This can break the bonds holding the tertiary structure in place –> change active site shape/ denatures enzyme.
• Enzyme denatures (fewer enzyme- substrate complexes are formed): rate of reaction decreases.

Question 14

Which bonds will mainly break in tertiary structure of enzyme if pH is too high/ too low?

2 bonds (MAINLY)

Answer 14

• Ionic
• Hydrogen.

Question 15

True or False

All enzymes in our body work at an optimal pH of 7.

Answer 15

• False.
• Different enzymes in body have a different optimal pH.

Question 16

If you have an insufficient substrate concentration, how does this affect the rate of reaction?

3 main points

Answer 16

• Decreased rate of reaction.
• Fewer collisions between the enzyme and substrate.
• Fewer enyme- substrate complexes formed.

Question 17

Why does the graph for rate of reaction against either enzyme- concentration or substrate concentration plateu?

Answer 17

• Reason for graph with enzyme concentration plateau –> empty active sites due to insufficient substrate (substrate = limiting factor.) Rate of reaction remains the same.
• Reason for graph with substrate concentration plateau –> enzyme active sites become saturated/ not enough enzymes (enzymes = limiting factor.) Rate of reaction remains the same.

Question 18

If you have an insufficient enzyme concentration, how does this affect the rate of reaction?

3 main points

Answer 18

• Enzyme active sites will become saturated with substrate, unable to work faster.
• Fewer enzyme- substrate complexes formed.
• Decreased rate of reaction.

Question 19

What are competitive inhibitors? What happens to competitive inhibitors at a high substrate concentration?

Answer 19

• Competitive inhibitors have same shape as substrate/ can bind to active site–> prevents substrate from binding/ reaction from occurring.
• High substrate concentration –> will flood out the active site/ knocking them out of the active site (ie. substrate out- competes the inhibitor.)

Question 20

What is the structure that is formed when an inhibitor binds to an enzyme’s active site?

Answer 20

• Enzyme- inhibitor complex.

Question 21

What are non- competitive inhibitors? Can substrates still bind to active site at high- substrate concentration?

Answer 21

• Non- competitive inhibitors bind to the enzyme (away from the active site.)
• Binding causes the active site to change shape, so substrate can no longer bind (even at a high concentration of substrate.)

Question 22

You are given graph with rate of reaction against substrate concentration with the curve for no inhibitor plotted. What would the curves for competitive inhibitor/ non- competitive inhibitor look like on the graph and why?

Answer 22

• Competitive inhibitor: curve is below curve of no inhibitor BUT at certain point, the rate of reactions allign/ rate of reaction returns to normal (because high substrate concentrations knocks off competitive inhibitors.)
• Non- competitive inhibitor: curve is below curve of competitive inhibitor (plateus very soon because high substrate concentration won’t knock inhibitor off)/ maximum rate of reaction reached early on.

Question 23

True or False

Enzymes only catalyse intracellular reactions.

Answer 23

• False enzymes catalyse both intracellular and extracellular reactions.

Question 24

What do intracellular and extracellular reactions determine?

Answer 24

• Intracellular and extracellular reactions determine structure and functions from cellular to whole-organism level.

Question 25

How can you work out the pH when you know the H+ concentration?

Answer 25

pH = -log (H+)

Question 26

How can you work out H+ concentration when you know pH?

Answer 26

(H+) =10⁻pH

Question 27

What value does (OH-) x (H+) concentrations give you?

Answer 27

10⁻pH