Enzymes

Question 1

What does an enzyme do with reference to activation energy?

Answer 1

Lowers the activation energy of a reaction

Question 2

Explain the induced fit model of enzyme action

Answer 2

Before the substrate bonds to the active site, they are not completely complimentary shape. As the substrate binds, the active site moulds to the shape of the substrate, similar to a sock moulding to the shape of a foot.

Question 3

What are the two main theories of how enzymes lower the activation energy of substrates?

Answer 3

• enzymes bring molecules together into positions so that the reaction can take place more easily
• enzymes place the molecules under stress so that the bonds break more easily

Question 4

What impact does temperature have on enzyme activity?

Answer 4

Every enzyme has an optimum temperature. If the temperature goes too high, then the kinetic energy increases, so the molecules vibrate more vigourously. This breaks the hydrogen and ionic bonds in the structure, and so the enzymes active site changes and it becomes denatured.

Question 5

What impact does pH have on enzyme activity?

Answer 5

A small change from the ideal pH would alter charges on the amino acids that make up the active site, so the substrate no longer binds. A large pH change breaks the hydrogen bonds, denaturing the enzyme.

Question 6

Explain competitive inhibitors

Answer 6

Competitive inhibitors are molecules with a similar shape to the enzyme substrate, and so they compete with the substrate for space on the active site. The effect of the competitive inhibitor can be reduced by adding more substrate.

Question 7

Explain non-competitive inhibitors

Answer 7

Non competitive inhibitors bind onto the allosteric site, the opposite side to the active site. This changes the shape of the active site, so no substrate molecules fit. Increasing the amount of substrate has no effect on non competitive inhibitors.

Question 8

Name two variables that will increase the rate of reaction and why.

Answer 8

• temperature: increasing temperature increases the kinetic energy of the molecules. This means that they move faster, and so collisions are more likely to occur.
• increasing concentration: by increasing the concentration of the enzymes or substrate, the rate of reaction will increase as there are more collision opportunities.

Question 9

Give the formula to calculate the pH of a solution using the hydrogen ion concentration

Answer 9

pH = -log10(H+)