Enzymes

Question 1

How does energy relate to bonds?

Answer 1

Energy is released when bonds form, and energy is required to break bonds.

Question 2

What is enthalpy?

Answer 2

Measurement of heat content.

Question 3

How do we work out the enthalpy?

Answer 3

The sum of the energy that is released when the bond is formed and the energy that is required to break that bond.

Question 4

What is entropy?

Answer 4

Entropy is randomness (gases have higher entropy then liquids), which is dependent on the temperature.

Question 5

How do we work out the change in free energy?

Answer 5

The change in enthalpy minus the change in entropy.

Question 6

How do we know if a reaction is spontaneous or not?

Answer 6

If the change in free energy is negative then the reaction is spontaneous, but if the change in free energy is positive then the reaction is not spontaneous.

Question 7

Why are enzymes important to us as humans?

Answer 7

Without enzymes, reactions would happen too slowly for life to be sustained.

Question 8

How do enzymes alter the activation energy?

Answer 8

Enzymes lower the activation energy, so that the reaction can occur with less energy.

Question 9

What are the three ways enzymes can act as catalysts?

Answer 9

1) Bind two substrate molecules together, in the correct position, to encourage a reaction between them.
2) When an enzyme binds to a substrate, the enzyme can rearrange the substrate’s electrons to create partial negative and positive charges, to favor a reaction.
3) The enzyme can strain a substrate molecule towards the transition stage, which will make it more likely to create a reaction.

Question 10

How are enzymes categorised?

Answer 10

Based on what they do.

Question 11

What is the Vmax?

Answer 11

The measure of catalytic power (activity of an enzyme): max rate of product formation.
Hardly ever reaches this!

Question 12

What is the Km?

Answer 12

The substrate concentration when the substate is at half of its Vmax.

Question 13

What do inhibitors do?

Answer 13

Lower enzyme activity.

Question 14

How can inhibitors be grouped?

Answer 14

Reversible or non-reversible. Then the reversible inhibitors can again be grouped as either competitive or non-competitive.

Question 15

How do people know where to group different inhibitors?

Answer 15

By observing the effect of the inhibitor on the Vmax and/or the Km.

Question 16

What two things can irreversible inhibitors do?

Answer 16

1) Could increase enzyme levels.
2) Separate very slowly from target enzyme.

Question 17

How does the irreversible inhibitor bind to the enzyme, and give an example for each?

Answer 17

1) Non-covalent forces - transition state analogues.
2) Covalent bond - suicide substrates.

Question 18

Where do competitive inhibitors bind to an enzyme?

Answer 18

Competitive inhibitors bind to the enzyme’s catalytic/active site. The competitive inhibitors have a shape that fits perfectly into the enzyme’s catalytic/active site.

Question 19

How does a competitive inhibitor work?

Answer 19

Competitive inhibitors bind with the enzyme’s catalytic/active site, which means that no substrate can bind while the competitive inhibitor is there.

Question 20

How can you tell if a inhibitor is competitive?

Answer 20

The Vmax is unaffected and the Km is increased, compared to if the enzyme had no inhibitor attached.

Question 21

Where do non-competitive inhibitors bind to an enzyme?

Answer 21

At a separate site to the enzyme’s catalytic/active site. The non-competitive inhibitor has a shape that does not fit into the enzyme’s catalytic/active site.

Question 22

How does a non-competitive inhibitor work?

Answer 22

Even though a substrate can still bind to the enzyme, as long as the non-competitive inhibitor is attached, it stops them from forming any products.

Question 23

How can we tell if a inhibitor is non-competitive?

Answer 23

The Vmax is lowered and the Km is the same, compared to if the enzyme had no inhibitor attached.

Question 24

What dose phosphorylation do?

Answer 24

Causes enzymes, that are subject to covalent modification, to be changed to active (by protein phosphatase) or inactive (by protein kinase). This effects the Vmax: ‘on’ or ‘off’.