PL.6

Question 1

What are enzymes?

Answer 1

Biological catalysts that are highly specific to reactions.

Question 2

What are two factors that enzymes are very sensitive to?

Answer 2

pH and temperature.

Question 3

Where does the catalysis take place in enzymes?

Answer 3

On the active site.

Question 4

What is the active site?

Answer 4

A cleft in the enzyme as a result of the tertiary structure that specific molecules can bind to and possibly react with.

Question 5

What is are specific molecules that can fit into the active site also known as?

Answer 5

Substrate.

Question 6

What part of the enzyme form bonds with the substrate?

Answer 6

The R groups on the amino acid residues.

Question 7

Is the bond between the enzyme and the substrate strong or weak and why?

Answer 7

Weak, because the bond must break when products are formed and need to leave the active site after the reaction.

Question 8

What does ES stand for?

Answer 8

Enzyme-substrate complex.

Question 9

What does EP stand for?

Answer 9

Enzyme-product complex.

Question 10

What is the mechanism for enzyme catalysis?

Answer 10

E + S → ES → EP → E + P, the enzyme is free to react with another substrate molecule once the reaction is finished.

Question 11

When the enzyme catalysis reaction is first order with respect to the substrate, which step is the rate determining step?

Answer 11

E + S → ES

Question 12

When is the reaction first order with respect to the substrate?

Answer 12

When the substrate concentration is low, and not all enzyme active sites are occupied, the rate of reaction depend on how frequent substrates and active sites encounter and therefore the number of substrates.

Question 13

When the enzyme catalysis reaction is zero order with respect to the substrate, which step is the rate determining step?

Answer 13

EP → E + P

Question 14

When is the reaction zero order with respect to the substrate?

Answer 14

When the substrate concentration is high, and all enzyme active sites are fully occupied, the rate of reaction depend on how fast products are made and active sites are freed and therefore it does not depend on the number of substrates.

Question 15

What are competitive inhibitors?

Answer 15

Molecules that can fit into the active site but cannot be catalyzed. They compete with substrates for the active sites, but once there, they do not react further and essential block the active site.

Question 16

What about an enzyme’s active site mean that it is often sensitive to pH changes?

Answer 16

The active site usually contain ionizable groups that will change will pH changes.

Question 17

How can high pH, alkaline conditions affect the COOH groups in the active site stopping it from functioning properly?

Answer 17

COOH groups can be ionized to COO-, meaning that it can no longer bind to substrates by hydrogen bonding.

Question 18

How can low pH, acidic conditions affect the NH2 groups in the active site stopping it from functioning properly?

Answer 18

NH2 groups can be ionized to NH3+, meaning that it can no longer bind to substrates by hydrogen bonding.

Question 19

If the shape of the active site is destroyed, the enzyme is said to be what?

Answer 19

Denatured.

Question 20

Why can enzymes become denatured if the pH is too far from the optimum pH?

Answer 20

Ionic bonds holding the enzyme’s tertiary structure may be broken meaning the overall shape changes and can no longer function properly.

Question 21

Why can high temperatures cause enzymes to become denatured?

Answer 21

Some bonds holding the tertiary structure together are weak dipole bonds and can easily be broken with temperature rise, this cause the shape of the enzyme to change and active sites are destroyed.