Enzyme

Question 1

What is an enzyme?

Answer 1

A biological catalyst that speeds up chemical reactions without being used up.

Question 2

What are enzymes made of?

Answer 2

Proteins (except ribozymes, which are RNA).

Question 3

What level of protein structure gives enzymes their specificity?

Answer 3

Tertiary structure.

Question 4

What is the active site?

Answer 4

The region of an enzyme where the substrate binds

Question 5

Why are enzymes specific?

Answer 5

The active site is complementary in shape to the substrate.

Question 6

What is meant by enzyme–substrate specificity?

Answer 6

Each enzyme catalyses only one reaction or a narrow range of reactions.

Question 7

Describe the lock and key model.

Answer 7

The substrate fits exactly into the active site, forming an enzyme–substrate complex.

Question 8

What is a limitation of the lock and key model?

Answer 8

It does not explain how the active site changes shape during binding

Question 9

Describe the induced fit model.

Answer 9

The active site changes shape slightly as the substrate binds, improving the fit.

Question 10

Why is the induced fit model more accepted?

Answer 10

It explains enzyme flexibility and lowering of activation energy.

Question 11

What is activation energy?

Answer 11

The minimum energy needed for a reaction to occur.

Question 12

How do enzymes lower activation energy?

Answer 12

By stabilising the transition state and bringing reactants together.

Question 13

What is an enzyme–substrate complex?

Answer 13

A temporary structure formed when a substrate binds to an enzyme.

Question 14

How does temperature affect enzyme activity?

Answer 14

Rate increases with temperature until optimum, then rapidly decreases.

Question 15

Why does enzyme activity decrease at high temperatures?

Answer 15

Denaturation — bonds break, active site shape changes.

Question 16

Is denaturation reversible?

Answer 16

Usually irreversible.

Question 17

How does pH affect enzymes?

Answer 17

pH alters the ionisation of amino acid side chains, affecting hydrogen and ionic bonds that maintain the enzyme’s tertiary structure. Changes in pH can distort the active site, reducing enzyme–substrate complex formation. Extreme pH causes denaturation, permanently reducing activity.

Question 18

Is denaturation reversible?

Answer 18

Usually irreversible.

Question 19

How does pH affect enzymes?

Answer 19

Changes ionic bonds, altering active site shape.

Question 20

What is optimum pH?

Answer 20

The pH at which enzyme activity is highest.

Question 21

How does increasing substrate concentration affect rate?

Answer 21

Rate increases until enzymes are saturated.

Question 22

What happens at enzyme saturation?

Answer 22

All active sites are occupied; rate is at maximum (Vmax).

Question 23

Q: How does enzyme concentration affect reaction rate?

Answer 23

Increasing enzyme concentration increases maximum rate if substrate is not limiting.

Question 24

What is an inhibitor?

Answer 24

A substance that reduces enzyme activity

Question 25

What is a competitive inhibitor?

Answer 25

A molecule similar to the substrate that competes for the active site.

Question 26

How can competitive inhibition be reduced?

Answer 26

By increasing substrate concentration

Question 27

What is a non-competitive inhibitor?

Answer 27

A molecule that binds away from the active site and alters enzyme shape.

Question 28

Can increasing substrate concentration overcome non-competitive inhibition?

Answer 28

No

Question 29

What is a cofactor?

Answer 29

A non-protein substance required for enzyme activity.

Question 30

Name types of cofactors.

Answer 30

A: Inorganic ions, prosthetic groups, coenzymes

Question 31

What is a coenzyme?

Answer 31

An organic molecule that transfers chemical groups between enzymes.

Question 32

Give an example of a coenzyme.

Answer 32

NAD (in respiration).

Question 33

How is enzyme activity measured in experiments?

Answer 33

Rate of product formation or substrate disappearance

Question 34

Why is a buffer used in enzyme experiments?

Answer 34

To maintain constant pH.

Question 35

Why are repeats used?

Answer 35

To improve reliability

Question 36

Q10= R2(rate at higher temperature ) ——————————— R1=(rate at lower temperature)

Question 37

Go over temperature coefficient when it’s not 10

Answer 37

Go over practice question

Question 38

Why is end-product inhibition important?

Answer 38

• Prevents over-production • Conserves energy and resources • Maintains homeostasis

Question 39

Which enzyme is usually inhibited?

Answer 39

The first enzyme in the metabolic pathway.

Question 40

How does the end product inhibit the enzyme?

Answer 40

It binds to an allosteric (non-active) site, changing the enzyme’s shape.

Question 41

What type of inhibition is end-product inhibition?

Answer 41

Non-competitive inhibition

Question 42

Why does end-product inhibition reduce enzyme activity?

Answer 42

The active site changes shape so the substrate can no longer bind.

Question 43

Q: Is end-product inhibition reversible?

Answer 43

Yes — when product concentration falls, inhibition is removed.

Question 44

Why doesn’t increasing substrate concentration overcome end-product inhibition?

Answer 44

: The inhibitor does not compete for the active site.

Question 45

Q: What is a cofactor?

Answer 45

A non-protein substance required for an enzyme to function.

Question 46

Are cofactors permanently attached to enzymes?

Answer 46

Not always — it depends on the type.

Question 47

Name the three types of cofactors.

Answer 47

Inorganic ions • Coenzymes • Prosthetic groups

Question 48

What are inorganic ion cofactors?

Answer 48

Charged ions that help enzyme activity.

Question 49

How do inorganic ions assist enzymes?

Answer 49

Form temporary bonds with enzyme or substrate • Stabilise enzyme–substrate complex

Question 50

Give an example of an inorganic ion cofactor.

Answer 50

Chloride ions (Cl⁻) for amylase.

Question 51

What is a coenzyme?

Answer 51

An organic molecule that transfers chemical groups or electrons between enzymes.

Question 52

Are coenzymes permanently attached?

Answer 52

No — they bind temporarily

Question 53

What happens to coenzymes during a reaction?

Answer 53

They are chemically altered, then later regenerated.

Question 54

Give an example of a coenzyme.

Answer 54

NAD (in respiration).

Question 55

What is a prosthetic group?

Answer 55

A non-protein molecule permanently attached to an enzyme

Question 56

How do prosthetic groups differ from coenzymes?

Answer 56

Prosthetic groups are permanently bound; coenzymes are not.

Question 57

Give an example of a prosthetic group.

Answer 57

Haem group in catalase

Question 58

State one difference between coenzymes and prosthetic groups

Answer 58

Coenzymes are temporarily bound, prosthetic groups are permanently attached