2.4 - Enzymes

Question 1

What can enzymes do?

Answer 1

• act as a biological catalyst causing reactions to speed up
• they can affect structures and functions of organisms

Question 2

What are intracellular enzymes?

Answer 2

Enzymes that work within the cell

Question 3

What are extracellular enzymes?

Answer 3

Enzymes that work outside of the cell

Question 4

What is an example of an intracellular enzyme?

Answer 4

Catalase:
They work inside the cell to catalyse the breakdown of hydrogen peroxide turning it into oxygen and water

Question 5

What is an example of an extracellular enzyme?

Answer 5

Amylase:
Secreted from the salivary glands to catalyse the hydrolysis of starch into maltose

Question 6

What are key features of an enzyme?

Answer 6

• globular protein
• has an active site that a complementary substrate binds to

Question 7

How is the shape of the active site determined?

Answer 7

It is determined by the enzymes tertiary structure

Question 8

What is made when and enzyme and substrate bind?

Answer 8

An enzyme substrate complex

Question 9

How does an enzyme lower the activation energy?

Answer 9

It lowers temperature that the reaction needs to happen at causing it to speed up the rate of reaction by forming an enzyme substrate complex

Question 10

What are the 2 theories about how enzymes work?

Answer 10

• lock and key method
• induced fit method

Question 11

How does the lock and key method work?

Answer 11

• the enzyme and the substrate are complementary
• this means that only certain substrates can go with enzymes
• the substrate fits into the active site of the enzyme
• this forms an enzyme substrate complex
• this then breaks the bonds in the enzymes causing the products to form

Question 12

How does the induced fit theory work?

Answer 12

• the enzyme and the substrate have similar shapes
• the substrate binds with the active site changing the shape slightly to fit more closely
• this forms an enzyme substrate complex
• bonds are either formed or broken to produce the product

Question 13

What are the 4 factors the effect the rate of enzyme activity/reactions?

Answer 13

• temperature
• pH
• enzyme concentration
• substrate concentration

Question 14

How does temperature effect enzyme activity?

Answer 14

• the temperature rises and the enzymes gain kinetic energy causeing them to vibrate more
• this means the rate of reaction increases
• when the temperature goes above a certain level it causes the enzymes to denature
• so the substrate is no longer able to bind to the active site

Question 15

What happens when an enzyme denatures?

Answer 15

It causes some of the bonds to break meaning the active site to change shape

Question 16

What is the symbol for temperature coefficient?

Answer 16

Q10

Question 17

How do you work out the temperature coefficient?

Answer 17

Rate at higher temperature / rate at a lower temperature

• temperatures have to be 10 degrees apart

Question 18

How does pH effect enzyme activity?

Answer 18

It causes the ionic and hydrogen bonds to break so the enzymes active site changes shape, this is because the bonds hold the enzymes tertiary structure together

Question 19

What happens when the pH is below the optimum?

Answer 19

It causes H+ ions to be produced (found in acids) which can break bonds that are holding the tertiary structure together so the active site changes

Question 20

What happens when the pH is above the optimum?

Answer 20

It causes OH- ions to be produced (found in alkalis) causing the bonds to break so the active site changes shape

Question 21

What is Pepsins optimum pH?

Answer 21

pH 2

Question 22

What is the optimum pH for most enzymes?

Answer 22

pH7

Question 23

How does the enzyme concentration affect the rate of reaction?

Answer 23

The more enzyme molecules there are in a solution, the more likely it is for a substrate to collide with it to form an enzyme substrate complex, so the rate of reaction increases

Question 24

What is the limiting factor when the enzyme concentration is increased?

Answer 24

The amount of substrate

Question 25

How does the substrate concentration affect the rate of reaction?

Answer 25

The higher the substrate concentration the faster the reaction because the enzyme and the substrate are more likely to collide so more active sights will be used

Question 26

What happens to the rate of reaction when the saturation point is reached (substrate concentration)?

Answer 26

All the active sites are used so adding more substrate will not make a difference. But eventually the concentration decreases with the theme that the reaction is taking place so the rate of reaction decreases overtime

Question 27

What is a cofactor (enzymes)?

Answer 27

It is a substrate that the enzyme needs to work

Question 28

What is an enzyme inhibitor?

Answer 28

They stop the enzyme from being able to work

Question 29

What is end product inhibition (enzymes)?

Answer 29

It is when one or more of the enzymes in a metabolic pathway is inhibited so it is unable to produce the correct product

Question 30

What is a competitive inhibitor (enzymes)?

Answer 30

The substrate and the inhibitor have the same shape so either can bind to the enzyme, the inhibitor blocks the substrate so it is unable to bind and form a product

Question 31

Are the effects of a competitive inhibitor reversible?

Answer 31

Yes, the inhibitor is able to detach so the effect is reversible

Question 32

What is a non-competitive inhibitor?

Answer 32

The inhibitor goes to the enzyme and binds to the allosteric site and changes the shape of the active site so the substrate is unable to bing to the enzyme to form a product

Question 33

Aren the effects of a non-competitive inhibitor reversible?

Answer 33

No, the inhibitor changes the protein shape of the enzyme so the active site is permanently changed

Question 34

What is an allosteric sit on an enzyme?

Answer 34

A part of the enzyme that is not near the active site

Question 35

How do competitive inhibitors affect the rate of reaction?

Answer 35

Competitive inhibitors make the rate of reaction slower because the inhibitors rarely block every active site, but it reaches the same end point

Question 36

How do non-competitive enzyme inhibitors affect the rate of reaction?

Answer 36

They lower the rate of reaction because the enzymes changes are irreversible so there are less enzymes to break the substrate, so the end point is significantly lower