Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are globular proteins that act as catalysts.

Question 2

What do catalysts do?

Answer 2

Catalysts alter the rate of a chemical reaction without undergoing permanent changes themselves.

Question 3

What are some advantages of using catalysts?

Answer 3

• Can be reused repeatedly, and are therefore effective in small amounts.
• Speed up chemical reactions.

Question 4

What is the activation energy?

Answer 4

Minimum amount of energy needed to activate the reaction.

Question 5

How do enzymes affect activation energy ( and therefore temperature too )?

Answer 5

Enzymes lower the activation energy, allowing reactions to take place at a lower temperature than normal.

Question 6

What is the difference between intracellular and extracellular?

Answer 6

• Intracellular - Inside Cells.

* Extracellular - Outside cells.

Question 7

What is the functional region of the enzyme?

Answer 7

The Active Site.

Question 8

What determines the shape of the enzyme?

Answer 8

The sequence of amino acids in the primary structure.

Question 9

What is the substrate?

Answer 9

Molecule on which the enzyme acts.

Question 10

How are enzyme-substrate complexes formed?

Answer 10

• When a substrate fits into an enzyme’s active site, it forms an enzyme substrate complex.

Question 11

How does the enzyme lower the activation energy required?

Answer 11

• if two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing repulsion between the molecules allowing for easier bonding.
• If the enzyme is catalysing a breakdown reaction, fitting in to the active site, puts a strain on bonds in the substrate.

Question 12

How do enzymes allow molecules to be more easily joined?

Answer 12

if two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing repulsion between the molecules allowing for easier bonding.

Question 13

How do enzymes allow molecules to be more easily split?

Answer 13

If the enzyme is catalysing a breakdown reaction, fitting in to the active site, puts a strain on bonds in the substrate, allowing for the molecule to more easily be split with less energy.

Question 14

What is the induced fit model?

Answer 14

• Active site forms as the enzyme and substrate interact.
• The substrate results in a change of proximity of the enzyme, and leads to a change in the enzyme that forms the functional active site.

Question 15

Why can enzymes only catalyse one reaction?

Answer 15

• Only one complementary substrate will fit the active site.
• Each different enzyme has a different tertiary structure, and therefore a differently shaped active site.
• if the substrate shape doesn’t match the active site, an enzyme substrate complex won’t be formed, and therefore a reaction will not place.

Question 16

What determines the shape of the active site?

Answer 16

The active site’s shape is determined by the enzyme’s tertiary structure, which is determined by the enzymes primary structure.

Question 17

What bond maintains the enzyme’s shape?

Answer 17

Hydrogen Bonds.

Question 18

What is required for an enzyme to carry out its function?

Answer 18

• Come into physical contact with its substrate.

* Have an active site which fits the substrate.

Question 19

How does temperature affect an enzyme activity?

Answer 19

• A rise in temperature increases the kinetic energy of molecules.
• Increase in kinetic energy results in molecules moving around quicker, which increases the amount of collisions, more substrates and enzymes will come together in a given time.
• The enzyme substrate complexes will have a higher energy and a more frequent collision rate, which increases the number of successful collisions, increasing the rate of reaction
• Eventually the temperature rises too high, and it causes the bonds in the enzyme molecule to break ( hydrogen bonds for example ), resulting in the enzyme and it’s active site changing shape, meaning the substrate can no longer bind to the active site, resulting in less enzyme substrate complexes forming, reducing the rate of reaction, the enzyme is now denatured.

Question 20

What is meant by an enzyme being denatured?

Answer 20

Where the enzyme ceases to function as a catalyst, denaturation is a permanent change.

Question 21

How does pH affect enzyme activity?

Answer 21

• Change in pH alters the charge son the amino acids that make up the active site of the enzyme.
• Change in charges means the substrate can no longer become attached to the active site, and so the enzyme substrate complex cannot be formed.

Question 22

What is the optimum pH value?

Answer 22

pH at which the enzyme fastest at.

Question 23

How does enzyme concentration affect rate of reaction/

Answer 23

• Once the enzyme has acted on its substrate, it is is able to act on another one of its substrate molecules, enzymes are not used up in a reaction.
• The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme substrate.
• Increase in enzyme concentration leads to an increase in rate of reaction.

Question 24

How does enzyme concentration affect rate of reaction if the substrate is limited?

Answer 24

• If the enzyme concentration is increased, excess substrate can be acted upon.
• If the substrate is the limiting factor, there will not be sufficient supply to all enzyme active sites after a certain point, therefore any increase in enzyme concentration beyond this point, ,will not have any affect on the rate of reaction.
• The rate of reaction will eventually stabilise at a constant amount, because the available substrate is already being used by the existing enzsyme molecules.

Question 25

How does substrate concentration affect rate of reaction?

Answer 25

• If the concentration of enzyme is fixed and the substrate concentration is slowly increased, the rate of reaction increases in proportion to the concentration of substrate.
• More substrate molecules means a greater chance of collision between substrate and enzyme, and so more active sites will be used, this however only applies up to a saturation point.
• Increase beyond the saturation point has no effect on the rate of reaction due to all available active sites being used up at the time.

Question 26

What are the two types of enzyme inhibition?

Answer 26

• Competitive inhibition

* Non competitive inhibition

Question 27

How does non competitive inhibition work?

Answer 27

• Non competitive inhibitors attach themselves to the enzyme to a binding site which is not the active site.
• Upon attaching to the enzyme, the inhibitor alters the shape of the enzyme, and thus its active site too.
• This results in the substrate no longer being able to bind to the active site, and therefore reducing the rate of reaction through a lack of enzyme substrate complexes being formed.

Question 28

Why is non competitive inhibition, not competitive?

Answer 28

Because the substrate and inhibitor do not compete for the same active site.

Question 29

How does substrate concentration affect non competitive inhibition?

Answer 29

Increasing the concentration of substrate won’t alter the effect of the inhibitor because they do not compete for the same active site.

Question 30

What is competitive inhibition?

Answer 30

• Competitive Inhibitors have a molecular shape similar to that of the substrate.
• This allows them to occupy the active site of an enzyme, they compete for the same site.
• When binding no reaction takes place, they block the active site so not substrate molecules can fit in it.

Question 31

How does substrate concentration affect competitive inhibition?

Answer 31

• How much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate.
• If there is a high concentration of inhibitor, it will take up nearly all the active sites, and very little substrate can bind to the enzyme.
• If there is a higher concentration of substrate, then the substrates chances of getting to an active site before the inhibitor increase.
Increasing the substrate increases the rate of reaction, reducing the effect of the inhibitor.

Question 32

Why is ‘’ competitive ‘’ inhibition, competitive?

Answer 32

Because the inhibitors share a similar shape to that of the substrate, and thus they compete for the same active site.