1b. ENZYMES

Question 1

Define what an enzyme is

Answer 1

A biological catalyst

Question 2

How do all enzymes speed up chemical reactions?

Answer 2

By lowering the activation energy

Question 3

Why must enzymes be water soluble?

Answer 3

Because most enzyme controlled reactions occur in the cytoplasm or tissue fluid, which are aqueous

Question 4

Give an example of an extracellular enzyme controlled reaction

Answer 4

Digestion

Question 5

Give an example of an intracellular enzyme controlled reaction

Answer 5

Respiration, photosynthesis, protein synthesis

Question 6

What is the functional part of an enzyme?

Answer 6

Active site

Question 7

What is the 3D shape of an enzyme’s active site determined by?

Answer 7

The type and position of the hydrogen, covalent, ionic and disulphide bonds in its tertiary shape

Question 8

Compare the shape of the substrate and the shape of the active site

Answer 8

They are complimentary

Question 9

When an ESC is formed, what two things are interacting?

Answer 9

The substrate and the enzyme

Question 10

Recall the two theories that describe how enzymes lower activation energy

Answer 10

Lock & key and induced fit

Question 11

In the lock and key model, is the active site always complimentary to the substrate?

Answer 11

Yes

Question 12

In the induced fit model, when is the active site not totally complimentary to the substrate?

Answer 12

Before the ESC is formed

Question 13

Describe how thebinding of the substrate lowers activation energy in the induced fit model

Answer 13

As the active site changes shape, it distorts the bondswithin thesubstrate, lowering the activation energy.

Question 14

Recall the two equations used to calculate rate of reaction

Answer 14

Product formed ÷ time & reactant formed ÷ time

Question 15

Define what Vmax is, and how it’s reached

Answer 15

The maximum rate of an enzyme-controlled reaction. It is reached when all the enzyme’s active sites are full.

Question 16

Explain why enzyme-controlled reactions have a high initial rate

Answer 16

Because the most ESC are formed at the beginning of a reaction

Question 17

Describe how to calculate the rate of reaction at a specific point on a graph, if the line is a curve

Answer 17

Calculate the tangent of the curve

Question 18

Explain why increasing temperature increases the rate of enzyme-controlled reactions

Answer 18

It increases the KE of the particles, which increases the frequency of collisions

Question 19

Explain how changing temperature may affect the rate of an enzyme controlled reaction

Answer 19

As temperature increases, rate increases

Question 20

Explain why changing temperature above the optimum may reduce the rate of reaction

Answer 20

Because the enzymes may denature

Question 21

Recall the equation to calculate pH

Answer 21

pH = -log10 [H+]

Question 22

Explain how changing pH may reduce the number of ESCs formed

Answer 22

As pH changes, more H+ causes the charges on the R groups of the amino acids in the active site to change, and the substrate will not be able to bind as easily. Less ESCs formed.

Question 23

Explain why changing pH causes the shape of an enzyme’s active site to change

Answer 23

The change in [H+] causes theionic and hydrogen bonds to break, which changes tertiary structure of active site. No ESCs can be formed.

Question 24

Explain why changing substrate concentration changes the rate of an enzyme-controlled reaction

Answer 24

It would change the frequency of collisions, changing the rate of ESCs formed

Question 25

Explain why changing enzyme concentration changes the rate of an enzyme-controlled reaction

Answer 25

It would change the frequency of collisions, changing the rate of ESCs formed

Question 26

Explain why and when the effect of changing enzyme and substrate concentration will no longer be seen

Answer 26

When Vmax is reached, when the reaction finishes, and when the enzyme becomes denatured

Question 27

What is the purpose of inhibitors in your body?

Answer 27

To control the rate of metabolic reactions

Question 28

Describe how competitive inhibitors work

Answer 28

The inhibtor has a similar shape to the substrate, and binds competitively to the active site, preventing ESCs forming

Question 29

Describe the shape of competitive inhibitors

Answer 29

The same as the substrate / complimentary to the active site

Question 30

Explain how Vmax can still be reached when a competitive inhibitor is used

Answer 30

By increasing substrate concentration, because this increases the probability of enzyme-substrate collisions

Question 31

Describe how non-competitive inhibition works

Answer 31

The bind to an allosteric site on the enzyme, changing the shape of the active site

Question 32

Explain why Vmax cannot be reached when a non-competitive inhibitor is used

Answer 32

Because they bind permanently to enzymes, so they are no longer available

Question 33

Describe how a molecule binding to an enzyme may act as an activator

Answer 33

It may bind to an allosteric site on the enzyme, changing the 3D shape of the active site to make it complimentary to the substrate