enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are biological catalysts

Question 2

What type of protein is an enzyme?

Answer 2

Globular proteins with complex and unique tertiary structures

Question 3

What do enzymes do?

Answer 3

They increase the rate of chemical reactions without being used up in the reaction themselves

Question 4

How do enzymes speed up reactions?

Answer 4

A certain amount of energy is required to start the reaction this is known as activation energy

An enzyme lowers the activation energy of a reaction

Question 5

What are intracellular enzymes and give an example?

Answer 5

Intracellular enzymes act within the cells that produce them

Catalyse -this catalyses the breakdown of hydrogen peroxide into oxygen and water. Which prevents the accumulation of toxic hydrogen peroxide inside cells.

Question 6

What are extracellular enzymes and give examples?

Answer 6

Extra cellular enzymes act outside the cells that produce and secrete them

Amylase - secreted by the salivary glands, pancreas and small intestine to breakdown starch into Maltose

Trypsin- secreted by the pancreas into the small intestine to breakdown proteins into smaller polypeptides

Question 7

How does an enzyme bind with the substrate?

Answer 7

• enzymes have unique tertiary structures which determine the shape of their active site

• this shape is complementary to the substrate

• the substrate binds the active site to form an enzyme substrate complex

• temporary bonds formed between the R groups within the active site and the substrate. These bonds lower the activation energy to help break down the substrate into products.

• the products are released from the active site, leaving the enzyme free to be used again

Question 8

What is the lock and key model?

Answer 8

1. The substrate collide with the active site of the enzyme. The substrate must be a complementary shape to the enzymes active site in order to fit
2. An enzyme substrate complex forms due to the lowered activation energy. An enzyme product complex is them formed
3. The enzyme modifies the substrate form in the product which is then released from the active site

Question 9

What is the induced fit model?

Answer 9

Active site changes shapes slightly to fit the substrate

Substrate enters active site, enzyme changes shape to fit, product leaves the active site

Question 10

What can affect the the rate of enzyme controlled reactions?

Answer 10

• Temperature
• pH
• Substrate concentration
• Enzyme concentration

Question 11

How is an enzyme denatured?

Answer 11

• the bonds break as more collision/vibration occur, changing the enzymes tertiary structure

• active site changes to the substrate no longer fits

• no enzyme substrate complexes conform

Question 12

How does temperature affect enzyme reactions?

Answer 12

Optimum temperature can vary

1. As temperature increases, the rate of reaction increases. The molecules have more kinetic energy, causing more collisions and enzyme substrate complexes
2. The maximum rate is reached at the optimum temperature, this is the temperature that enzyme works the fastest
3. As the temperature increases past the optimum temperature, the rate of reaction decreases until the reaction stops, too much kinetic energy causes the active site to change shape in the enzyme denatures.

Question 13

What is the temperature coefficient (Q10)?

Answer 13

The temperature coefficient is a value that shows how much the rate of reaction changes when the temperature is increased by 10°

Question 14

How do you work out the temperature coefficient?

Answer 14

Q10= R2/R1

R2- the rate of reaction at the higher temperature (+10°)
R1-the rate of reaction at the lower temperature

Question 15

How does pH affect enzyme reactions?

Answer 15

Optimum pH can vary

1. Below the optimum pH, the rate of reaction is low or zero. In acidic conditions, positive hydrogen ions break ionic/hydrogen bonds and denature enzymes
2. The maximum rate of reaction is reached at the optimum pH, this is the pH the enzymes work the fastest
3. Above the optimum pH, the rate of reaction is low or zero. In alkaline solutions, OH negative ions break ionic bonds or hydrogen bonds and denatured enzymes.

Question 16

How does substrate concentration affect enzyme reactions?

Answer 16

1. As the substrate concentration increases, the rate of reaction decreases. There are more substrate molecules to form more enzyme substrate complexes
2. As the substrate concentration increases further, the rate of reaction plateaus. This is the saturation point, which is when all active sites are occupied by a substrate and enzyme concentration becomes the limiting factor.

Question 17

How does enzyme concentration affect enzyme reactions?

Answer 17

1. As the enzyme concentration increases, the rate of reaction increases. There are more enzyme molecules to form more enzyme substrate complexes
2. As the enzyme concentration increases further, the rate of reaction plateaus. All the substrate molecules available are being acted upon a substrate concentration becomes the limiting factor.

Question 18

What are inhibitors?

Answer 18

Inhibitors are molecules that bind to enzymes to reduce their activity

Question 19

What is a reversible inhibitor?

Answer 19

These form weak bonds (E.g hydrogen or ionic) with the enzyme and can be changed

Question 20

What are irreversible inhibitors?

Answer 20

These form strong bonds (e.g covalent) with the enzyme and can’t be changed

Question 21

What are competitive inhibitors?

Answer 21

These bind to the active site

Question 22

What are non-competitive inhibitors?

Answer 22

These bind away from the active site (allosteric)

Question 23

How to competitive inhibitors work?

Answer 23

Competitive inhibitors have a similar shape to the substrate and so they bind to the active site of the enzyme. This stops the substrate from binding and this reduces the formation of enzyme substrate complexes. This result in a decrease in the rate of enzyme catalyse reactions

Most competitive inhibitors are reversible as they only temporarily bind to the enzyme

The higher the substrate concentration, the more likely the substrate will bind the active sites rather than the inhibitor molecules

Question 24

How do non-competitive inhibitors work?

Answer 24

This binding changes the tertiary structure of the enzyme, causing the active site to change shape

This results in the active site no longer be complementary to the substrate, than the substrate and enzyme can’t bind. Less enzyme substrate complex is formed and the rate of the enzyme catalysed reaction decreases.

Non-competitive inhibitors do not compete with the substrate to bind the active site, so increasing the amount of substrate has no effect on the rate of reaction

Question 25

What are coenzymes?

Answer 25

These are organic cofactors and are usually derived from vitamins

Question 26

What are prosthetic groups?

Answer 26

These are cofactors that are tightly bounded to enzymes E.g zinc is the prosthetic group for the enzyme carbonic anhydrase