Enzymes

Question 1

What is an enzyme and what type of protein are they?

Answer 1

Enzymes are globular proteins that act as biological catalysts

Question 2

Define metabolism

Answer 2

Refers to all the reactions of the body

Question 3

What is an anabolic reaction?

Answer 3

Building up molecules
e.g protein synthesis

Question 4

What is a catabolic reaction?

Answer 4

Breaking molecules down
e.g digestion

Question 5

What is an enzyme- substrate complex?

Answer 5

Enzyme acts on substrate forming temporary bonds at the active site

Question 6

How are enzymes secreted from cells?

Answer 6

By exocytosis

Question 7

What are the two models of enzyme action?

Answer 7

The lock and key model
The induced fit model

Question 8

How do enzymes use induced fit to catalyse a reaction?

Answer 8

1. Active site not complementary to substrate
2. As substrate binds, active site changes shape to form enzyme-substrate complex
3. This stresses bonds in substrate causing reaction to occur

Question 9

For an enzyme to catalyse a reaction, it must…

Answer 9

Come into contact with substrate
Substrate must be complementary to active site
Must collide with enough energy at the right orientation

Question 10

How do enzymes actually speed up the rate of reaction?

Answer 10

Lower the activation energy

Question 11

What is an exergonic reaction?

Answer 11

Energy released

Question 12

What is an endergonic reaction?

Answer 12

Energy absorbed

Question 13

What is a catalyst?

Answer 13

A substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction

Question 14

What is an enzyme inhibitor and what does it do?

Answer 14

Substances that directly or indirectly affect the functioning of the active site of a specific enzyme and so prevent the substrate binding, preventing the formation of enzyme substrate complexes and therefore decrease the rate of reaction

Question 15

What are the two types of inhibitors?

Answer 15

Competitive and non-competitive

Question 16

How does a competitive inhibitor work?

Answer 16

Have a similar structure to the substrate, so they can bind to the active site of an enzyme. Binding of a competitive inhibitor to the active site is reversible, so when it leaves the active site, another molecule can enter (substrate or inhibitor)

Question 17

How does a non-competitive inhibitor work?

Answer 17

Binds to an enzyme at a site that is NOT the active site (allosteric site). Binding of the inhibitor causes a change in the tertiary structure of the enzyme, therefore changing the shape of the active site. This means that the active site is no longer complementary to the substrate so the substrate can no longer bind (so no enzyme substrate complex formed and no reaction)

Question 18

How can competitive inhibition be overcome?

Answer 18

Increase substrate concentration

Question 19

What does negative feedback do?

Answer 19

speed up/slow down/stop enzymes to control the metabolic pathway based on the cells demands

Question 20

What determines the shape of an enzyme’s active site?

Answer 20

Tertiary structure – held in place by selection of bonds – ionic/disulphide/hydrogen

Question 21

What is pH?

Answer 21

A measure of its hydrogen ion
concentration

Question 22

Define limiting factor

Answer 22

A factor is limiting when an increase in its value causes an increase in the rate of reaction

Question 23

Name 4 factors that could affect the rate of enzyme action

Answer 23

• Temperature
• pH
• Enzyme concentration
• Substrate concentration