Enzymes (Biochemistry Chapter 2)

Question 1

If an enzyme ends with the word synthase, what two types of enzymes can it be?

Answer 1

If an enzyme ends with the word synthase then the enzyme must be a ligase or lyase.

Question 2

If an enzyme ends with the word synthetase, what class of enzyme must it be?

Answer 2

If the enzyme ends in synthetase, then it must be a ligase.

Question 3

What enzyme requires ATP to join two large molecules together, usually of the same type?

Answer 3

An enzyme that joins two large molecules together by harnessing the energy from ATP, it must be a ligase.

Question 4

What class of enzymes often employ coenzyme donors?

Answer 4

Transferases often employ coenzyme donors.

• Ex: Coenzyme A

Question 5

Digestive enzymes, such as trypsin and pepsin, are often what class of enzyme?

Answer 5

Digestive enzymes are mostly hydrolases.

Question 6

What class of enzymes often form rings or multiple bonds to reform octets?

Answer 6

Lyases often form rings or multiple bonds to reform octets.

Question 7

How does the active site of an enzyme lower the activation energy?

Answer 7

The active site of an enzyme lowers the activation energy by forcing the substrates into positions that favor the transition state.

Question 8

How do enzymes affect the thermodynamics and kinetics of a reaction?

Answer 8

Enzymes do not affect the thermodynamics at all. Instead, enzymes lower the activation energy and make the overall reaction proceed faster towards equilibrium.

• Reactions are reversible, but occur more slowly than the foward reaction.

Question 9

What is the opposite of a hydration or hydrolysis reaction catalyzed by a hydrolase?

Answer 9

Dehydration synthesis (condensation) is the opposite of hydrolysis. Hydrolases catalyze both the forward and reverse of these reactions.

Question 10

If an enzyme is named “[substrate] + ase” then what class of enzyme is it?

Answer 10

If an enzyme is named “[substrate] + ase” then it is a hydrolase enzyme.

Question 11

What class of enzyme joins and splits molecules without water?

Answer 11

Lyases join and split molecules without using water.

Question 12

What are the 5 mechanisms in which enzymes can lower the activation energy?

Answer 12

1. Stabilize the transition state
   
   • Dissipation of torsional strain and favorable bond formation
   • Eyx: SN2 reactions
2. Adjust the microenvironment
   
   • Adjusts the local environment’s pH through the exclusion of water
3. Adjust substrate proximity
   
   • Increases the frequency of favorable collisions
4. Transient covalent bonding
   
   • Substrates briefly contact active site residues sequentially
5. Reactant Destabilization
   
   • Create torsional strain or hydrophobic-hydrophili reactions

Question 13

What are the two enzyme-substrate binding theories?

Answer 13

The two enzyme-substrate binding theories are

1. Induced fit
2. Lock and key

Question 14

What happens to the rate of a reaction that is catalyzed by an enzyme as the temperature is increased by 10°C?

Answer 14

For every 10°C increase up to 37°C (body temp.), the reaction of rate catalyzed by an enzyme doubles.

Question 15

At what pH do pancreatic enzymes optimally function within the small intestine?

Answer 15

Pancreatic enzymes optimally function at the small intestine’s pH of 8.5

Question 16

What affect do salt increases have on enzymatic activity?

Answer 16

In vivo (in the body), increasing the salt concentration does not have any affect on enzymatic activity. However in vitro (in a test tube), increasing the salt concentration reduces the enzymatic activity.

Question 17

How does competitive inhibition affect K_m and V_max?

Answer 17

Competitive inhibition increases K_m but does not affect V_max as increasing the substrate concentration a significant amount will overcome the inhibition.

Question 18

What is noncompetitive inhibition and how does it affect K_m and V_max?

Answer 18

Noncompetitive inhibition is when an inhibitor binds to an allosteric site on an enzyme. K_m remains unchanged however V_max decreases.

• Inhibitor has equal affinity for the enzyme and enzyme-substrate complex (ES).

Question 19

What is uncompetitive inhibition and how does it affect K_m and V_max?

Answer 19

Uncompetitive inhibition occurs when an inhibitor binds to the enzyme-substrate complex (ES) and prevents the substrate from leaving the active site. Uncompetitive inhibition decreases both K_m and V_max.

Question 20

What is mixed inhibiton and how does it affect K_m and V_max?

Answer 20

Mixed inhibition is a mix between noncompetitive and uncompetitive inhibition. Mixed inhibition occurs when an inhibitor has different affinities for the enzyme and enzyme-substrate complex.

• If the inhibitor binds preferentially to the enzyme only, then K_m will increase.
• If the inhibitor binds preferentially to the enzyme-substrate complex, then K_m will decrease.
• V_max decreases in all mixed inhibition scenarios.

Question 21

If a Lineweaver-Burk plot has parallel lines plotted, what type of inhibtion is the enzyme?

Answer 21

If parallel lines are plotted on a lineweaver-burk plot, the enzyme must be uncompetitive inhibition.

Question 22

What type of inhibition has equal affinity for the enzyme and enzyme-substrate complex?

Answer 22

In noncompetitive inhibition, the inhibitor has equal affinity for the enzyme and enzyme-substrate complex.