2.1.4 Enzymes - Enzymes

Question 1

Define Anabolic reactions

Answer 1

Reactions that build up molecules

Question 2

Define Catabolic reactions

Answer 2

Reactions that break down molecules

Question 3

Define Metabolism

Answer 3

Combination of anabolic and catabolic reactions

Question 4

Define Catalyst

Answer 4

A substance that speeds up reactions without changing the produced substances.

Question 5

Define Metabolic pathway

Answer 5

Sequence of enzyme-controlled reactions.

Question 6

Define Specificity

Answer 6

Only able to catalyse specific reactions

Question 7

Define Substrate

Answer 7

The molecule(s) the enzyme works on.

Question 8

Define Product

Answer 8

Molecule(s) produced by enzymes.

Question 9

Define Activation Energy

Answer 9

The minimum amount of energy needed for a reaction to start.

Question 10

What are enzymes?

Answer 10

Enzymes are Biological Catalysts that help to speed up metabolic reactions.

• Remain unchanged at the end of a reaction, so can be used again
• Can catalyse large numbers of Substrates into Products
• Increase a rate of reaction by lowering its activation energy
• Can be intracellular, or extracellular
• Can be prevented from working by molecules called Enzyme Inhibitors

Question 11

What is a catabolic reaction?

Answer 11

A Catabolic reaction is an example of a hydrolysis reaction, where water is added to an enzyme substrate complex to break the bond between the substrate to form an enzyme-product complex.

Question 12

What are the stages/flowchart of enzymes?

Answer 12

Enzyme + substrate  enzyme-substrate complex  (substrate breaks to form)  enzyme-product complex  enzyme + product

Question 13

What is the lock and key hypothesis?

Answer 13

The lock and key hypothesis suggests that the enzyme is like a lock and the substrate is like a key. This means that the substrate is very specific to the active site just like a key fits into a lock, (substrate fits into the active site).
However now scientists use/believe the induced fit hypothesis rather than the lock and key hypothesis.

Question 14

What is the induced fit hypothesis?

Answer 14

The induced fit hypothesis suggests that the active site is flexible and only assumes its catalytic conformation after the substrate molecules bind to the site. When the product leaves the enzyme the active site reverts to its inactive state.
This means that substrates always have a complementary fit to the active site of the enzyme. It also means that substrates are not very specific to enzymes however this means that there is a better fit between the substrate and active site of the enzyme.

Question 15

What factors affect enzymes?

Answer 15

• Temperature
• pH
• substrate concentration

Question 16

How does Temperature affect enzymes?

Answer 16

Low temperature = Low rate of reaction:
Enzymes have too little kinetic energy and move slowly. Few successful collisions between enzyme and substrate leads to low rate of reaction.

Optimum temperature = High rate of reaction:
Enzymes have a lot of kinetic energy and move quickly. Lots of successful collisions between enzyme and substrate leads to high rate of reaction.

High temperature = low rate of reaction:
Heat breaks the bonds maintaining the tertiary structure of the enzyme. The active site becomes denatured and substrate no longer fits. No successful collisions lead to a low rate of reaction.

Question 17

How does pH affect enzymes?

Answer 17

Low pH = Low rate of reaction:
Acidity breaks the bonds maintaining the tertiary structure of the enzyme. The active site becomes denatured and substrate no longer fits. No successful collisions lead to a low rate of reaction.

Optimum pH = High rate of reaction:
Many collisions between working enzyme and substrate means high rate of reaction.

High pH = low rate of reaction:
Alkalinity breaks the bonds maintaining the tertiary structure of the enzyme. The active site becomes denatured and substrate no longer fits. No successful collisions lead to a low rate of reaction.

Question 18

How does substrate concentration affect enzymes?

Answer 18

Low substrate concentration = Low rate of reaction:
Few substrate molecules limits the chance of successful collisions between enzyme and substrate. Rate of reaction is low

High substrate concentration = High rate of reaction:
More substrate molecules increase the chance of successful collisions between enzyme and substrate. Rate of reaction is high.

Question 19

Define temperature coefficient, Q10?

Answer 19

The Temperature coefficient, Q10, of a reaction (or process) is a measure of how much the rate of reaction increases with a 10oC rise in temperature.