Exam 2

Question 1

An enzyme ____.

a) is an inorganic catalyst
b) is an organic catalyst
c) is a source of energy for endergonic reactions
d) can bind to nearly any molecule
e) increases the E(subA) of a reaction

Answer 1

An enzyme is an organic catalyst.

Enzymes are proteins that behave as catalysts.

Question 2

A(n) _______ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the subtrate.

Answer 2

competitive

Question 3

A(n) _______ inhibitor binds to a site on the enzyme that isn’t the active site

Answer 3

noncompetitive

Question 4

Usually, a(n) __ inhibitor forms a covalent bond with an amino acid side group withing the active site, which prevents the substrate from entering the active site or prevents catalytic activity.

Answer 4

Irreversible

Question 5

The competitive inhibitor competes with the substrate for the _______ on the enzyme

Answer 5

Active site

Question 6

Enzyme inhibitors disrupt normal interactions between an enzyme and its ________.

Answer 6

Substrate

Question 7

When the noncompetitive inhibitor is bonded to the enzyme, the shape of the _______ is distorted.

Answer 7

Enzyme

Question 8

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, reaction has stopped completely. What can you do to regain the activity of the enzyme?

a) Removing the irreversible inhibitor should get the reaction working again.
b) The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.
c) Adding more substrate will increase the rate of reaction
d) Adding more inhibitor should get the reaction up to speed again

Answer 8

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

Question 9

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down.
What can you do to speed the reaction up again?
a) Add more inhibitor to speed up the reaction
b) Add more substrate; it will outcompete the inhibitor and increase the reaction rate
c) Increase the temperature
d) Increase the pH

Answer 9

Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme’s shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor’s shape and structure should be.