Enzymes

Question 1

enzymes

Answer 1

proteins (usually end in -ase) that act as biological catalysts

Question 2

how do enzymes catalyze reactions?

Answer 2

by lowering the activation energy required for the reaction to occur; more molecules can then enter the transition state and proceed to products

Question 3

what do enzymes bind?

Answer 3

substances that are reacting called substrates, in which enzymes release the products upon completion of reaction

Question 4

steps in an enzyme-catalyzed reaction

Answer 4

1. binding of the substrate
2. conversion of substrate to product
3. release of product

Question 5

protein conformation in enzymatic reactions

Answer 5

the shape or “conformation” of the molecule brings the substrates together so that the reaction can proceed and the active site of the molecule is dependent on the a.a.’s that are located there

Question 6

zinc as a cofactor

Answer 6

in addition to the a.a.’s lining the active site, there may be another group, such as the zinc ion in carbonic anhydrase; it is held in place by binding to 3 histidines in the active site and the +ve charge attracts electrons from water to make it easer to remove one of the H’s for the rxn to proceed

Question 7

enzyme cofactors

Answer 7

molecules required to activate enzyme

Question 8

coenzymes

Answer 8

organic molecules that are not proteins and are usually synthesized from vitamins; they contribute functional groups that help catalyze the rxn but are not very active on their own

Question 9

lock and key enzyme model

Answer 9

shape of enzyme active site allows a specific substrate to fit; explains enzyme specificity but not the enzymes ability to stabilize the transition state

Question 10

induced fit model

Answer 10

allows for flexibility of the enzyme in binding to the substrate, and so is thought to be the most accurate; binding of the substrate induces changes in the shape or “conformation” of the enzyme

Question 11

pH dependence

Answer 11

enzymes function at an optimal pH, which usually corresponds w/ physiological pH (some work best in acidic conditions, e.g. pepsin, the stomach enzyme that breaks down proteins at a pH of 1.5-2; above 5 it is denatured)

Question 12

temperature and concentration

Answer 12

for both factors, rate of reaction of an enzyme increases

Question 13

optimal temp. for most enzyme function

Answer 13

normal physiological temp; 37ºC

Question 14

enzyme inhibition

Answer 14

a competitive inhibitor is a molecule w/ a similar shape to one of the substrates and when the inhibitor binds instead of the substrate, the rxn cannot occur, and the product is not produced

Question 15

competitive inhibitors

Answer 15

bind to the enzyme reversibly or irreversibly; reversible inhibitors only inhibit when they are bound in the active site, many can be displaced by increasing the concentration of substrate while
irreversible inhibitors do not detach and the enzyme action is permanently shut down

Question 16

noncompetitive (allosteric) inhibition

Answer 16

binds to part of the enzyme away from the active site which prevents the reaction from proceeding by changing the conformation of the enzyme; either the affinity of the enzyme for the substrates is reduced or the rxn can’t occur b/c of the change in shape

Question 17

cytochrome P450 enzymes

Answer 17

• large family of enzymes important in drug metabolism, particularly the liver
• oxidize hydrophobic compounds making them more soluble to allow excretion vs. build up
  (CYP enzymes are also intestinal cells, this is where grapefruit juice interferes, statins are not metabolized and can build up to toxic levels in the blood)