1.4.2 Many proteins are enzymes

Question 1

What is an enzyme?

Answer 1

A globular protein that acts as a biological catalyst by speeding up the rate of a chemical reaction.

Question 2

How do enzymes speed up the rate of a chemical reaction?

Answer 2

They provide an alternative pathway for the reaction, one with a lower activation energy.

Question 3

What is activation energy?

Answer 3

The minimum amount of energy required for a reaction to occur.

Question 4

What is the induced fit model?

Answer 4

The enzyme structure is not rigid; the active site changes shape to fit the substrate, putting strain on the substrate to weaken bonds and lower activation energy.

Question 5

Are enzymes globular or fibrous proteins?

Answer 5

Globular.

Question 6

What determines the 3D structure of enzymes?

Answer 6

The order and sequence of amino acids.

Question 7

When does an enzyme-substrate complex form?

Answer 7

When the substrate binds with the active site.

Question 8

What holds enzyme-substrate complexes together?

Answer 8

Temporary bonds that form.

Question 9

What is specificity in regards to enzymes?

Answer 9

One enzyme has a small number of substrates due to the exact molecular fit between the substrate and active site.

Question 10

How does the active site of an enzyme cause a high rate of reaction?

Answer 10

The enzyme-substrate complex puts strain on the bonds in the substrate, making them easier to break, which reduces activation energy.

Question 11

How do high temperatures affect enzyme activity?

Answer 11

They break many H bonds, altering the shape of the active site and making it harder for the enzyme to form an enzyme-substrate complex.

Question 12

How can changes in pH affect enzyme activity?

Answer 12

Excess H+ or OH- ions change interactions between amine and carboxyl groups, influencing H bonds in the active site and reducing successful collisions.

Question 13

How can changes in pH denature the enzyme?

Answer 13

It further changes the shape of the active site, preventing enzyme-substrate complexes from forming.

Question 14

Where do competitive inhibitors bind?

Answer 14

The active site.

Question 15

What must competitive inhibitors be like to bind to the active site?

Answer 15

They must be complementary to the active site and similar in shape to the substrate.

Question 16

Are competitive inhibitors permanently bound to the active site?

Answer 16

No.

Question 17

How can the effects of a competitive inhibitor be overcome?

Answer 17

By increasing the substrate concentration.

Question 18

Where do non-competitive inhibitors bind to an enzyme?

Answer 18

The allosteric site.

Question 19

Can non-competitive inhibitors be a different shape to the substrate?

Answer 19

Yes, they don’t have to be complementary to the active site.

Question 20

Does increasing substrate concentration overcome the effects of a non-competitive inhibitor?

Answer 20

No.

Question 21

How do non-competitive inhibitors work?

Answer 21

They alter the shape of the active site, changing the tertiary structure, so the substrate is no longer complementary to the active site.

Question 22

Where do coenzymes bind to?

Answer 22

The active site.

Question 23

Are coenzymes involved in the reaction?

Answer 23

No.

Question 24

Are coenzymes chemically altered/used up in the reaction?

Answer 24

No.

Question 25

Are coenzymes a non-protein substance?

Answer 25

Yes.

Question 26

Are cofactors involved in the reaction?

Answer 26

Yes.

Question 27

Are cofactors temporarily modified in the reaction?

Answer 27

No.

Question 28

Where do cofactors bind?

Answer 28

The active site.

Question 29

Are cofactors a non-protein substance?

Answer 29

Yes.

Question 30

Describe the induced-fit model of enzyme action.

Answer 30

Substrate binds to the active site, active site changes shape to distort bonds in the substrate, reducing activation energy.

Question 31

How does a competitive inhibitor decrease the rate of an enzyme-controlled reaction?

Answer 31

The inhibitor has a similar shape to the substrate, fits/binds to the active site, preventing/reducing enzyme-substrate complex formation.

Question 32

Explain how the active site of an enzyme causes a high rate of reaction.

Answer 32

It lowers activation energy, the induced fit causes the active site to change shape , and the enzyme-substrate complex causes bonds to form/break.

Question 33

How does the formation of an enzyme-substrate complex increase the rate of reaction?

Answer 33

It reduces activation energy due to stress on bonds.

Question 34

How does a decrease in temperature affect the rate of an enzyme-controlled reaction?

Answer 34

Molecules move less, reducing the chance of collision.

Question 35

(a) In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase: * only breaks down maltose * allows this reaction to take place at normal body temperature.

Answer 35

1. Tertiary structure 2. Active site complementary to substrate 3. Description of induced fit; 4. lowers activation energy 5. forms enzyme-substrate complex;

Question 36

Descibe competitive and non- competitive inhibition of an enzyme. (5marks)

Answer 36

- reduce binding of enzyme to substrate/ preventing formation of ES complex competetive- inhibitor similar shape to substrate - Binds to AS of enzymes - can be overcome by more substrate Non -comp - inhibitator binds to siter on enzyme other than active site - prevents formation of active site/ changes shape of active site

Question 37

Describe one similarity and one difference between the induced fit model of enzyme activity and the lock and key model.

Answer 37

sim - substrate binds to AS - enzyme substrate complexes formed diff As changes shape, but doesn't change in lock and key AS not complimentary to substrate with induced fit, but is complementary in lock and key

Question 38

Describe the structural nature of enzymes

Answer 38

globular proteins specific tertiary structure complementary to substrates substrates bind to active site of enzymes

Question 39

Difference between competitive and non competitive inhibitors

Answer 39

competitive - bind the active site of enzymes, blocking substrate form binding Non competitive inhibitors - bind to different site on enzyme - causing a conformational change that alters the shape of the active site

Question 40

Digestive enzymes

Answer 40

active site, specific teriratry structure, can only bind to, form enzymes substrate complexes

Question 41

Discuss the induced fit model of enzyme substrate interaction

Answer 41

substrates collide with enzymes active site form an enzyme substrate complex induces slight changes in shape of active site making it more complementary to the substrate which facilitates the reaction

Question 42

Explain how enzymes reduce the activation energy of reactions

Answer 42

binds substrate to active site straining the bonds in the substrates allows their conversion into products

Question 43

Explain the relationship between substate concentration and enzyme activity

Answer 43

increase substrate conc increases rate of reaction as more enzyme substrate collisions there is a max rate when all active sites are occupied enzymes saturation

Question 44

How does enzyme concentration affect reaction rate?

Answer 44

increasing enzyme conc increase rate as there are more enzymes available to catalyse substrate molecules are instantly converted to products

Question 45

How does temperature affect the rate of enzyme controlled reactions?

Answer 45

increasing temp initially increases rate of reaction by providing more kinetic energy for successful enzyme substrate collision optim temp - enzymes denature decreasing the rate as the active site loses its complementary shape

Question 46

pH

Answer 46

-log10 (H+)

Question 47

Formation of an enzyme-substrate complex increases the rate of reaction. Explain how.

Answer 47

1. Reduces activation energy; 2. Due to bending bonds OR Without enzyme, very few substrates have sufficient energy for reaction;

Question 48

Lyxose binds to the enzyme. Suggest a reason for the difference in the results shown in Figure 5 with and without lyxose.

Answer 48

1. (Binding) alters the tertiary structure of the enzyme ; 2. (This causes) active site to change (shape); 3. (So) More (successful) E-S complexes form (per minute) OR E-S complexes form more quickly OR Further lowers activation energy;