Enzymes

Question 0

Extracellular enzymes

Answer 0

Enzymes that catalyse reactions outside the cell

Question 1

Endothermic animals

Answer 1

Animals with the ability to maintain their internal body temperatures independent of their surroundings

Question 2

Intracellular enzymes

Answer 2

Enzymes that catalyse reactions inside the cell

Question 3

List the five characteristics that all enzymes share

Answer 3

• They are all globular proteins
• They act as catalysts
• They are specific to their reaction and substrate
• They have an active site
• Their activity is affected by temperature and pH

Question 4

Name the structure of an enzyme and what it’s made of

Answer 4

Tertiary structure - primary and secondary structures make it up

Question 5

Catalyst

Answer 5

A molecule (or element) that speeds up a chemical reaction but does not get used up. At the end of the reaction, the catalyst remains unchanged.

Question 6

Name the suffix given to enzymes in their name

Answer 6

• ase

Question 7

Activation energy

Answer 7

The amount of energy that must be applied for a reaction to proceed. Different reactions require different levels of activation energy. Enzymes lower this value

Question 8

Explain the lock and key theory

Answer 8

The substrate is the key, and the active site of the enzyme is the lock. As the substrate fits into the active site, an enzyme substrate complex is formed. The substrate will then form a product and the enzyme can be reused.

Question 9

Explain the induced fit hypothesis

Answer 9

Induced fit is when the enzyme molecule changes its shape slightly to accommodate the substrate. It makes the active site fit more closely around the substrate and forms an enzyme substrate complex.

Question 10

Describe the graph of rate of reaction versus temperature on enzyme activity

Answer 10

Steady rise to the optimum temperature and a steeper decrease.

Question 11

Explain why the rate of reaction decreases when the temperature reaches a certain point.

Answer 11

Because the enzymes are being denatured and the bonds in their tertiary structure are being broken so the active site is no longer complementary with the shape of the substrate molecule. This decreases the number of successful collisions and therefore the number of product molecules formed.

Question 12

Denaturation

Answer 12

This changes the tertiary structure of an enzyme such that it cannot function and it’s function cannot be restored. It does not change the primary structure of an enzyme.

Question 13

Optimum pH

Answer 13

The pH value at which the rate of an enzyme controlled reaction is at its maximum. Each enzyme has a specific optimum pH.

Question 14

A buffer (solution)

Answer 14

A chemical solution that resists changes in pH by maintaining a constant level of hydrogen ions in solution.

Question 15

How does the pH of a solution change the tertiary structure of an enzyme?

Answer 15

The hydrogen and ionic bonds which give the enzyme its shape are altered as the H+ ions in the acid (or lack of them in alkaline solutions) interfere.

Question 16

What happens if you increase the concentration of substrate to the rate? Can you describe the graph?

Answer 16

As the concentration of substrate increases, the number of collisions between enzyme and substrate molecules occur more often. More enzyme substrate complexes form, so more product is formed. The rate increases.

However a point will eventually be reached where the reaction rate is at its maximum. Here, all active sites are occupied. The rate levels off here.

Question 17

What happens if you increase the enzyme concentration? Can you describe the graph?

Answer 17

Much like increasing the substrate concentration, there will be an increase in rate but there will reach a maximum point where all the substrate molecules have formed enzyme substrate complexes and therefore cannot react any more.

Question 18

Limiting factor

Answer 18

A factor in a situation where, if all other conditions are kept constant, increasing the concentration of that factor alone will increase the reaction rate.

Question 19

Enzyme inhibitor

Answer 19

An enzyme inhibitor is any substance or molecule that slows down the rate of an enzyme p- controlled reaction by affecting the enzyme molecule in some way.

Question 20

How do competitive inhibitors work?

Answer 20

These inhibitors have similar shapes to the real substrate. This means they can occupy the active site to form enzyme inhibitor complexes but there is no formation of product because the inhibitor is not identical to the substrate.

Question 21

How do non competitive inhibitors work?

Answer 21

These inhibitors do not compete with substrate molecules for the actives site. Instead, they attach to the enzyme mole rule in a region away from the active site.