2.5 Enzymes

Question 1

Define enzyme.

Answer 1

globular proteins that act as catalysts, speeding up reactions by lowering the activation energy

Question 2

Define active site.

Answer 2

the part of an enzyme that interacts with the substrate

Question 3

Define denaturation.

Answer 3

The loss of an enzyme’s quaternary, tertiary, and secondary structure such that they no longer function as enzymes.

Question 4

Define substrate.

Answer 4

substances converted into products by enzymes in biochemical reactions

Question 5

Explain enzyme-substrate specificity.

Answer 5

The shape and chemical properties of the active site and the substrate match each other. This allows the substrate to bind, but not other substances. Substrates are converted into products while they are bound to the active site and the products are then released. And so in order for a reaction to occur, there must be a match between the enzyme and substrate.

Question 6

Differentiate between the Induced Fit and Lock & Key models?

Answer 6

Induced Fit: conformational change of the active site to fir the substrate after binding
Lock & Key: substrate and active site are complementary

Question 7

What are the three stages of an enzyme-catalyzed reaction?

Answer 7

1. The substrate(s) binds to the active site of the enzyme.
2. While the substrate(s) is(/are) bound to the active site, they change into different chemical substances, which are the products of the reaction.
3. The products separate from the active site, leaving it vacant for substrates to bind again.

Question 8

How are enzyme-catalyzed reactions affected by the molecular motion of particles?

Answer 8

Both substrates and enzymes with active sites are moving in solution (usually) and so collisions occur because of the random, independent movements of both the substrate and enzyme. The more often they collide, the more often the two will bind.

Question 9

Explain the effects of temperature on the rate of enzyme-controlled reactions. How does rate of reaction graph look?

Answer 9

• In liquids, as temperature increases, so too does the kinetic energy and therefore motion of particles, increasing the chance of collision. However, when temperatures increase, bonds in the enzyme vibrate more and so they are more likely to break, denaturing the enzymes.
• It increases linearly to a point and then drops off as enzymes are denatured more rapidly.

Question 10

Explain the effects of pH on the rate of enzyme-controlled reactions. How does enzyme activity graph look?

Answer 10

• When the hydrogen ion concentrations are higher or lower than an enzymes optimum pH level, the enzyme’s structure begins to denature.
• The graph rapidly increases and then decreases in enzyme activity around the optimum pH.

Question 11

Explain the effects of substrate concentration on the rate of enzyme-controlled reactions. How does rate of reaction graph look?

Answer 11

• As the concentration of substrates increases, so does the enzyme activity. However, as substrate concentration rises, more and more active sites are blocked. As a result, increases in the rate of enzyme activity plateaus.
• Increase and then a plateau.

Question 12

What happens to the active site in denaturation?

Answer 12

The active site is altered so the substrate can no longer bind or, if it does bind, it cannot catalyze reactions.

Question 13

What does it mean for an enzyme to be immobilized?

Answer 13

It is attached to another material or into aggregations so that movement is restricted.

Question 14

What are some benefits of immobilized enzymes?

Answer 14

• Can be easily separated from the products of the reaction, preventing contamination of products
• Enzyme may be recycled
• Increases stability of enzymes to changes in temperature and pH
• Substrates can be exposed to higher enzyme concentrations