Enzymes

Question 1

Define metabolism and what is the name of the sequences?

Answer 1

All the reactions of the body. They are called metabolic pathways.

Question 2

Name and describe the two types of metabolic pathways.

Answer 2

• Anabolic reactions- building up molecules.
• Catabolic reactions- breaking down molecules.

Question 3

List the general properties of enzymes.

Answer 3

• They speed up reactions
• They are not used up in the reactions
• They are not charged
• They have a high turn-over number (they catalyse many reactions per second)

Question 4

Describe the structure of enzymes

Answer 4

Proteins with tertiary structures. The protein chain folds into spherical or globular shapes with hydrophilic R groups on the outside of the molecule, making enzymes soluble.

Question 5

What are the three sites where enzymes act?

Answer 5

• Extracellular- by being secreted from cells by exocytosis. E.G. Amylase from salivary glands to act in the mouth
• Intracellular in solution- act in solution inside cells. E.G. enzymes that catalyse the breakdown of glucose
  -Intracellular, membrane-bound- may be attached to membranes. E.G. on the cristae of mitochondria

Question 6

What is an enzyme-substrate complex?

Answer 6

When an enzyme temporarily bonds with a substrate at the active site.

Question 7

Describe the lock and key model.

Answer 7

The substrate has ‘enzyme specificity’ and will only fit with the specific enzyme needed. The active site and substrate fit perfectly.

Question 8

Describe the induced fit model.

Answer 8

The idea that the active site alters shape to accommodate for the substrate as it is not enzyme specific.

Question 9

Define activation energy.

Answer 9

The minimum energy that must be put into a chemical system for a reaction to occur.

Question 10

How do enzymes lower the activation energy?

Answer 10

They work by modifying the substrate .

Question 11

List the factors that affect enzyme action.

Answer 11

• Temperature- the higher the temperature usually speeds up enzyme action but too hot will denature the enzymes, reducing enzyme action.
• pH- most enzymes have an optimum pH. Extremes of pH denature enzymes.
• Substrate concentration- varies with enzyme concentration. They are the limiting factor.
• Enzyme concentration- varies with substrate concentration.

Question 12

Define enzyme inhibition.

Answer 12

The decrease in the rate of an enzyme- controlled action by another molecule (inhibitor).

Question 13

Describe competitive inhibition.

Answer 13

They have a complementary shape to the active site and are similar to the substrate, so they compete for the active site against the substrate.

Question 14

Describe non-competitive inhibition.

Answer 14

The non-competitive inhibitor binds to the enzyme at the allosteric site which is not the active site so they do not compete with the substrate.

Question 15

Define immobilised enzymes.

Answer 15

Enzyme molecules bound to and inert material over which the substrate molecules move.

Question 16

Why are immobilised enzymes beneficial?

Answer 16

Enzymes that are free are more prone to enzyme instability due to temperature, pH etc. Immobilising enzymes creates a more stable environment, allowing reactions to occur at higher temps/ more extreme pH levels etc.

Question 17

List the advantages of immobilised enzymes.

Answer 17

• Increased stability and function over a wider range of conditions
• Products are not contaminated with enzyme
• Enzymes are easily recovered for reuse
• Several enzymes with differing conditions can be used
• Enzymes are easily added/ removed