Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts regulating biological processes in living organisms

Enzymes catalyse a wide range of intracellular and extracellular reactions.

Question 2

What determines the specific function of an enzyme?

Answer 2

The protein nature and tertiary structure of the enzyme

The specific structure allows enzymes to catalyse specific reactions.

Question 3

What is the role of enzymes in relation to activation energy?

Answer 3

Lowering the activation energy required for reactions to take place

This increases the rate of reaction.

Question 4

How do enzymes lower the activation energy?

Answer 4

Through the formation of enzyme-substrate complexes

This process facilitates the reaction by stabilizing the transition state.

Question 5

What is the Lock and Key model?

Answer 5

An early model suggesting the active site of an enzyme is rigid and complementary to the substrate

This model has been replaced by the induced-fit model.

Question 6

What is the induced-fit model of enzyme action?

Answer 6

A model suggesting that the active site of an enzyme is flexible and changes shape to fit the substrate

This model accounts for the dynamic nature of enzyme-substrate interactions.

Question 7

What is enzyme specificity?

Answer 7

The ability of enzymes to act on specific substrates

Some enzymes, like amylase, act on a single substrate, while others, like lipases, target specific chemical bonds.

Question 8

What happens when the substrate binds to the active site?

Answer 8

The enzyme and substrate form an enzyme-substrate complex

This complex is crucial for the catalytic activity of the enzyme.

Question 9

What does the induced-fit model suggest about the active site of an enzyme?

Answer 9

The active site is flexible and can slightly change its shape

The correct substrate induces a change in shape, allowing it to mould around the substrate.

Question 10

In the induced-fit model, how does the active site change when the substrate binds?

Answer 10

The active site changes shape slightly as the substrate binds

This change makes the active site and substrate complementary in shape.

Question 11

What happens to the enzyme at the end of the reaction in the induced-fit model?

Answer 11

The enzyme remains unchanged

This is a key characteristic of enzyme reactions.

Question 12

Fill in the blank: The active site and the substrate become _______ in shape after binding.

Answer 12

complementary

This allows for a more likely reaction to occur.

Question 13

What are some essential terms associated with the topic of enzymes?

Answer 13

• active site
• complementary
• denaturation
• tertiary structure

These terms are crucial for gaining maximum marks in exam answers.

Question 14

True or false: The Lock and Key model is the only model used to explain how enzymes catalyse reactions.

Answer 14

FALSE

The induced-fit model is also important to understand enzyme catalysis.

Question 15

What happens to the rate of enzyme reactions as substrate concentration increases?

Answer 15

Initially increases, then levels out at Vmax

The rate reaches a constant maximum rate when all active sites are occupied.

Question 16

What is Vmax in the context of enzyme reactions?

Answer 16

The maximum rate of reaction

Occurs when all active sites of the enzyme are saturated with substrate.

Question 17

When the active sites of all enzyme molecules are occupied, what is the limiting factor for the rate of reaction?

Answer 17

Concentration of enzyme

At saturation, increasing substrate concentration does not increase the reaction rate.

Question 18

What must be added to increase the rate of reaction at high substrate concentrations?

Answer 18

More enzyme

This is necessary when all active sites are saturated.

Question 19

As the reaction progresses, what happens to the concentration of substrate?

Answer 19

Decreases

This decrease leads to a slower rate of product formation.

Question 20

What occurs to the rate of product formation as the concentration of substrate decreases?

Answer 20

Decreases

Fewer collisions between substrate and active site result in less enzyme-substrate complexes.

Question 21

What happens to the concentration of product as all substrate is converted?

Answer 21

Levels off

The reaction reaches completion when all substrate has been converted to product.

Question 22

In an enzyme-controlled reaction, what is the relationship between time and substrate concentration?

Answer 22

Substrate concentration decreases over time

Initially high substrate concentration leads to a greater rate of reaction.

Question 23

What happens to the rate of reaction when the concentration of substrate is in excess and enzyme concentration increases?

Answer 23

Increases

More enzyme molecules lead to more active sites available, increasing collisions and enzyme-substrate complexes.

Question 24

At low temperatures, enzymes are less efficient because the rate of reaction is slowed down by the reduced _______.

Answer 24

kinetic energy

Reduced kinetic energy of reactant molecules slows down the reaction.

Question 25

What effect does an increase in temperature have on the **rate of reaction** up to the optimum temperature?

Answer 25

Increases ## Footnote More kinetic energy results in more collisions and enzyme-substrate complexes formed.

Question 26

What occurs to the enzyme's **tertiary structure** when the temperature exceeds the optimum level?

Answer 26

Denaturation ## Footnote Hydrogen and ionic bonds are broken, altering the active site shape.

Question 27

Denaturation of proteins at temperatures above **50°C** is usually _______.

Answer 27

permanent ## Footnote The tertiary structure is irreversibly altered, preventing substrate binding.

Question 28

What happens to the **active site** of an enzyme when it denatures?

Answer 28

Changes shape ## Footnote The active site is no longer complementary to the substrate, leading to fewer enzyme-substrate complexes.

Question 29

The formation of more **enzyme-substrate complexes** occurs due to an increase in what?

Answer 29

Enzyme concentration ## Footnote More active sites available increase the likelihood of collisions.

Question 30

True or false: An increase in temperature always increases the rate of reaction.

Answer 30

FALSE ## Footnote Rate of reaction increases up to the optimum temperature; beyond that, denaturation occurs.

Question 31

At what temperature does the enzyme reaction show the **highest kinetic energy**?

Answer 31

60°C ## Footnote At this temperature, the reaction proceeds at a very fast rate initially due to many collisions between enzyme and substrate molecules.

Question 32

What happens to the enzyme at **60°C** during the reaction?

Answer 32

Enzyme denaturation ## Footnote High kinetic energy causes hydrogen bonds to break, altering the active site and preventing substrate binding.

Question 33

At **25°C**, why does the reaction proceed at a slow rate?

Answer 33

Low kinetic energy ## Footnote Fewer collisions between enzyme and substrate molecules result in a slower reaction rate.

Question 34

At **37°C**, how does the reaction rate compare to that at **25°C**?

Answer 34

Faster rate ## Footnote More kinetic energy leads to more frequent collisions between enzyme and substrate molecules.

Question 35

What is the outcome for substrate conversion at **25°C** and **37°C**?

Answer 35

All substrate is converted to product ## Footnote Both temperatures level out at the same point because the initial substrate concentrations were the same.

Question 36

True or false: At **60°C**, all substrate is converted into product.

Answer 36

FALSE ## Footnote The reaction stops before all the substrate is converted due to enzyme denaturation.

Question 37

What is the relationship between **temperature** and the rate of enzyme reactions?

Answer 37

Higher temperature increases reaction rate up to a point ## Footnote Beyond a certain temperature, enzymes denature and reaction rates decrease.

Question 38

What does line C represent in the graph?

Answer 38

Reaction at 25°C ## Footnote It shows a slow reaction rate with all substrate eventually converted to product.

Question 39

What does line B represent in the graph?

Answer 39

Reaction at 37°C ## Footnote It indicates a faster reaction rate with all substrate converted to product.

Question 40

What does line A represent in the graph?

Answer 40

Reaction at 60°C ## Footnote It shows an initial fast reaction rate that eventually stops due to enzyme denaturation.

Question 41

What is the **optimum pH** for enzymes?

Answer 41

The pH at which the rate of reaction is at a maximum ## Footnote Most enzymes are active over a narrow pH range.

Question 42

True or false: Most enzymes are active over a **broad pH range**.

Answer 42

FALSE ## Footnote Most enzymes are active over a narrow pH range.

Question 43

What can cause **denaturation** of enzymes?

Answer 43

Very different pHs from the optimum ## Footnote Denaturation alters the enzyme's structure and function.

Question 44

How does a change in pH affect the **ionic charges** of enzymes?

Answer 44

It alters the ionic charges of acidic and basic groups ## Footnote This change can lead to the breaking of hydrogen and ionic bonds.

Question 45

What happens to the **tertiary structure** of an enzyme when pH changes significantly?

Answer 45

It is altered, affecting the shape of the active site ## Footnote This alteration prevents the substrate from binding.

Question 46

Fill in the blank: A change in pH can break **_______** and ionic bonds in enzymes.

Answer 46

hydrogen ## Footnote Breaking these bonds can lead to loss of the enzyme's tertiary structure.

Question 47

What is the effect of pH on the **active site** of enzymes?

Answer 47

The shape of the active site is altered ## Footnote This alteration prevents substrate binding and affects enzyme activity.

Question 48

What forms when the substrate binds to the enzyme's active site?

Answer 48

Enzyme-substrate complexes ## Footnote These complexes are crucial for the catalytic activity of enzymes.

Question 49

What are **enzyme inhibitors**?

Answer 49

Chemicals that slow down the rate of enzyme catalyzed reactions ## Footnote They can affect the efficiency of enzymes in biochemical processes.

Question 50

What is a **competitive inhibitor**?

Answer 50

An inhibitor with a similar structure to the normal substrate that competes for the active site ## Footnote It reduces the rate of reaction by preventing substrate binding.

Question 51

How can **competitive inhibition** be reduced?

Answer 51

By adding more substrate ## Footnote At high substrate concentrations, the substrate can outcompete the inhibitor for the active site.

Question 52

In the presence of a **competitive inhibitor**, what happens to the rate of reaction?

Answer 52

It is reduced ## Footnote The inhibitor occupies the active site, preventing substrate binding.

Question 53

What does the graph show regarding **competitive inhibitors**?

Answer 53

The effect on the rate of reaction at different substrate concentrations ## Footnote It illustrates how the presence of an inhibitor alters reaction rates.

Question 54

What is the role of the **active site** in enzyme activity?

Answer 54

The location where substrate molecules bind to the enzyme ## Footnote It is crucial for the enzyme's catalytic function.

Question 55

What is a **non-competitive inhibitor**?

Answer 55

An inhibitor that is not similar in structure to the substrate ## Footnote It combines at a position other than the active site.

Question 56

Where does a **non-competitive inhibitor** bind?

Answer 56

At a position other than the active site ## Footnote This binding alters the tertiary structure and shape of the active site.

Question 57

What happens to the **active site** of an enzyme when a non-competitive inhibitor is present?

Answer 57

The shape of the active site is changed ## Footnote This alteration prevents the substrate from attaching as it is no longer complementary.

Question 58

The degree of **inhibition** by a non-competitive inhibitor is dependent on what factor?

Answer 58

The amount of inhibitor present ## Footnote A high concentration of substrate will not reduce non-competitive inhibition.

Question 59

True or false: A high concentration of substrate can reduce **non-competitive inhibition**.

Answer 59

FALSE ## Footnote Non-competitive inhibition is unaffected by substrate concentration.

Question 60

In the presence of a **non-competitive inhibitor**, what happens to the substrate's ability to bind?

Answer 60

The substrate cannot bind to the active site ## Footnote This is due to the change in the shape of the active site.

Question 61

What does the graph of a non-competitive inhibitor show regarding the **rate of reaction**?

Answer 61

The rate of reaction is affected by the presence of the inhibitor ## Footnote It illustrates the difference in reaction rates with and without the inhibitor.