enzymes

Question 1

Define

Metabolism

Answer 1

All the chemical reactions that take place in cells.

Question 2

Define

Catabolism

Answer 2

Reactions in which large molecules are broken down into smaller ones. These reactions release energy.
Example: digestion

Question 3

Anabolism

Answer 3

Process in which small molecules are built up into larger ones. These reactions require energy.
Example: protein synthesis.

Question 4

Define

Enzyme

Answer 4

A biological catalyst that speeds up chemical reactions by lowering the activation energy. It is not consumed or altered in the reaction.

Question 5

** What do catalysts do?

Answer 5

Lower the activation energy while not being consumed in the reaction.

Question 6

Define

Substrate

Answer 6

The molecule on which an enzyme acts.

Question 7

Define

Active site

Answer 7

The part of the enzyme molecule that combines with the substrate.

Question 8

Define

Enzyme-substrate complex

Answer 8

A temporary molecule formed when the substrate binds to the enzyme.

Question 9

Explain

Lock and key model

Answer 9

The shape of the enzyme (key) is always complementary to the shape of the substrate (lock). Therefore, they will fit exactly together to form the enzyme-substrate complex.

Question 10

Explain

Induced-fit model

Answer 10

When the enzyme and substrate join, they form weak bonds that cause the shape of the enzyme to change, creating complementary shapes.

Question 11

7 factors affecting enzyme activity.

Answer 11

1. Temperature
2. pH
3. Enzyme concentration
4. Substrate concentration
5. Product concentration
6. Cofactors
7. Enzyme inhibitors

Question 12

How does temperature affect the rate of enzyme activity?

Answer 12

• As the temperature increases, the enzymes and substrates move faster (higher kinetic energy) so the active sites and substrates collide more often, speeding up the rate of activity.
• (Problem) However, continually raising the temperature causes hydrogen bonds in the enzyme’s active site to break, causing it to change shape (denature), so the substrate(s) can no longer bind to them. this results in a decline in the rate of activity.

Question 13

Define

pH

Answer 13

A measure of the concentration of hydrogen ions in a substance. (Stands for potential of hydrogen)

Question 14

How does pH affect the rate of enzyme activity?

Answer 14

• Enzymes work at specific pH.
  
  • e.g., pepsin works in acidic conditions.
• Changing pH alters the enzyme’s shape, affecting rate of activity.

Question 15

How does enzyme concentration affect the rate of enzyme activity?

Answer 15

• As enzyme concentration increases, there are more active sites available for substrates to bind to.
• Unless the substrate increases, the product(s) produced remains the same (conservation of mass).

Question 16

How does substrate concentration affect the rate of enzyme activity?

Answer 16

• As the substrate concentration increases, so does the rate of activity until all the active sites are occupied.
• We are limited by the available active sites, so rate no longer increases. this is called the turnover number.

Question 17

How does product concentration affect the rate of enzyme activity?

Answer 17

The products must be continually removed otherwise the rate of reaction will slow because it becomes more difficult for the substrate molecules to make contact with the enzyme molecules (because products are in the way).

Question 18

Define

Cofactor

Answer 18

Ions or non-protein molecules that catalyse a reaction by changing the shape of the active site so that the enzyme can combine with the substrate. Without a cofactor, the enzyme is intact but cannot function.

Question 19

Define

Coenzymes

Answer 19

Cofactors that are non-protein organic molecules. Many vitamins function as coenzymes.

Question 20

Define

Enzyme inhibitors

Answer 20

Substances that slow or even stop the enzyme’s activity.
- May be used by cells to control reactions so that the products are produced in specific amounts.
- Many drugs are enzyme inhibitors.
- E.g., penicillin inhibits an enzyme in bacteria that is involved in construction of the cell wall.