BB 6 - Enzymes

Question 1

What are enzymes?

Answer 1

Highly specific globular proteins that are biological catalysts produced by living things.

Question 2

What do enzymes do?

Answer 2

Speed up chemical reactions in cells and organisms

Question 3

What is the main purpose of enzymes?

Answer 3

Allow reactions to be regulated and controlled

Question 4

How is an enzyme-substrate complex formed?

Answer 4

When a substrate binds to the active site of the enzyme.

Question 5

What happens to the enzyme after the substrate binds?

Answer 5

The enzyme changes shape slightly to fit the substrate more exactly (induced-fit model).

Question 6

What is the induced-fit model?

Answer 6

Occurs after a substrate molecule binds to the active site of the enzyme, where the enzyme slightly changes shape to fit the substrate more exactly.

Question 7

How do enzymes increase reaction rate?

Answer 7

1. Lower activation energy of a biological reaction.
2. Bring substrate molecules together in correct orientation for a reaction to occur (induced-fit model).
3. Put stress on chemical bonds of the substrate molecule, causing the bonds to break and reform with less energy input.

Question 8

What factors can influence enzyme activity?

Answer 8

Temperature
pH
Inhibitors (Competitive and Non-competitive)
Reactant Concentration
Enzyme Concentration

Question 9

How does temperature affect enzyme activity?

Answer 9

Different enzymes work at different optimal temperatures.

Question 10

What happens when the enzyme is at optimal temperature?

Answer 10

The enzyme maintains its shape and has greatest number of successful collisions with substrate molecules.

Question 11

What happens when the temperature of a reaction is too low?

Answer 11

The kinetic energy in the enzyme and substrate molecules is low, which causes less successful collisions to occur.

Question 12

What increases as temperature increases?

Answer 12

Kinetic energy

Question 13

What happens when the temperature of a reaction is too high?

Answer 13

The protein denatures (loses tertiary shape and converts back to secondary or primary structure.

Question 14

How do proteins denature when the temperature is too high?

Answer 14

The high amount of energy (heat) overcomes the secondary bonding (hydrogen bonding) between the amino acids.

Question 15

What happens when an enzyme loses its tertiary shape?

Answer 15

Can no longer recognise and bind to its substrate due to loss of specificity, slowing down reaction rate.

Question 16

What happens when the pH is lower or higher than the optimum?

Answer 16

The enzyme denatures causing it lose its shape, slowing down reaction rate.

Question 17

How many types of inhibitors are there?

Answer 17

Two

Question 18

What are the two types of inhibitors?

Answer 18

Competitive

Non-competitive

Question 19

How do competitive inhibitors affect enzyme activity?

Answer 19

Have similar shape to the substrate molecule which competes to bind to the active site of the enzyme.

Question 20

How can the effect of competitive inhibitors be overcome?

Answer 20

Increasing the substrate concentration to increase chances of substrate binding to the active site of the enzyme instead of the inhibitor.

Question 21

How do non-competitive inhibitors affect enzyme activity?

Answer 21

Have a different shape to the substrate molecule, which binds to the allosteric site instead of the active site.

When the inhibitor binds, the shape of the enzyme becomes distorted, causing the active site to be no longer complementary to the substrate molecule.

They do not compete with substrate molecules for binding.

Question 22

How can the effect of non-competitive inhibitors be overcome?

Answer 22

The effect cannot be overcome by increasing substrate concentration.

Question 23

How does reactant / substrate concentration affect enzyme activity?

Answer 23

Increases the rate of a biological reaction.

Question 24

When is the maximum reaction rate achieved?

Answer 24

When all the enzyme’s active sites are occupied by substrate molecules

Question 25

How can the reaction be increased when all enzymes are occupied?

Answer 25

Increasing enzyme concentration as increasing the substrate concentration will create plateaus in reaction rate.

Question 26

When is maximum reaction achieved in terms of enzyme concentration?

Answer 26

When the substrate concentration becomes the limiting factor.