Exam 2 (6) - Enzymes

Question 1

What is a Catalyst?

Answer 1

Speed up chemical reactions but are unchanged by the reaction

Question 2

What is an enzyme?

Answer 2

Large Protein —> Catalysts

Question 3

What are substrates?

Answer 3

Reactant of enzymatically accelerated reaction.

Question 4

Each enzyme accelerates specific reactions. (T/F)

Answer 4

True

Question 5

Each enzyme in metabolic pathway requires a unique and specific enzyme ( T/F)

Answer 5

True

Question 6

What is necessary for the end product to appear in a metabolic pathway?

Answer 6

All enzymes need to be present and functional. ( precisely regulated)

Question 7

What is the energy of activation?

Answer 7

• reactants are often reluctant to participate in reactions
• energy must be added to 1 or more reactants
• enzymes operate by LOWERING the energy of activation

Question 8

How do enzymes lower the energy of activation?

Answer 8

1) bring substrates into contact w/ one another

2) strain/ stretch the bonds in reactants

3) changing the local environment of reactant

4) Adding or removing functional group to or from substrate

Question 9

What is the cleft/grove on the surface of the large enzyme?

Answer 9

active site

Question 10

What does the substrate bind to?

Answer 10

The active site

Question 11

What is the induced fit model?

Answer 11

shape change forces substrates together insinuating bond

Question 12

What happens when a specific substrate binds to an active site?

Answer 12

It causes the active site to change shape

• induced fit model

Question 13

The same enzyme can catalyze the forward reaction and the reverse reaction. T/F

Answer 13

T, both a degradation reaction and a synthesis reaction are possible with the same enzyme

Question 14

General sequence for an enzymatically catalyzed sequence
?

Answer 14

E+Substrate–> E-S complex–> E + Products

Question 15

How would a degradation reaction work with the general sequence for enzyme reactions?

Answer 15

• Enzyme complexes with a single substrate molecule
• Substrate Is broken apart into two product molecules ( Hydrolysis)
• Enzyme walks away unharmed

Question 16

How would a synthesis reaction work with the general sequence for enzyme reactions?

Answer 16

• Enzyme complexes with two substrate molecules
• Substrates are joined together and released as a single product molecule

Question 17

What are the factors that affect enzyme reactions?

Answer 17

• Enzyme concentration
• Substrate concentration
  -Vmax
  -temperature
• pH
• denaturation,
  -cofactors
• coenzymes (vitamins)
• modulators or inhibitors

Question 18

How does Enzyme concentration affect the rate of a reaction?

Answer 18

The rxn rate increases as enzyme conc increases ( w/excess substrate) — a linear relationship

Question 19

How does substrate concentration affect the rate of a reaction?

Answer 19

• enzyme activity increases w/ substrate concentration to a point ( saturation)
• more collisions between substrate molecules and the enzyme
• Vmax

Question 20

What is Vmax?

Answer 20

plateau where nearly all active sites are occupied by substrates

Question 21

What is the relationship between Km and affinity?

Answer 21

Lower Km =Higher affinity

Question 22

What is Km

Answer 22

1/2 Vmax

Question 23

What is the relationship between enzymes and temperature?

Answer 23

temp. increase = enzyme activity increase
( too high for too long = denaturation)

Question 24

What is the relationship between enzymes and pH?

Answer 24

most enzymes are optimized for a particular ph

Question 25

What are cofactors

Answer 25

inorganic molecules required to activate enzymes

Question 26

What are coenzymes

Answer 26

organic molecules required to activate enzymes

Question 27

what is a modulator?

Answer 27

enhances enzyme activity

Question 28

what is an inhibitor?

Answer 28

blocks enzyme activity

Question 29

What are the different kinds of enzyme inhibitors?

Answer 29

• competitive inhibition
  -noncompetitive inhibition
  -feedback inhibition
• irreversible inhibition

Question 30

What is competitive inhibition?

Answer 30

Substrate and inhibitor are both able to bind to the active site

• normally inhibitors can bind more tightly, and high affinity
• inhibitor temporarily binds to active site blocking normal molecule

Question 31

What is noncompetitive inhibition?

Answer 31

the inhibitor binds not at the active site, but at the allosteric site

Question 32

what is the allosteric site?

Answer 32

Some other pocket or groove on that enzyme that binds with the inhibitor or modulator

Question 33

why is feedback inhibition important?

Answer 33

• can be both competitive or non-competitive
• found in all cells
• an important regulatory process in enzyme function.

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Question 34

what is feedback inhibition?

Answer 34

Where some end product feeds back into an early step and shuts the enzyme off temporarily ( until it is needed again)

Question 35

What is irreversible inhibition?

Answer 35

Materials that irreversibly inhibit an enzyme.

Question 36

poison

Answer 36

Materials that irreversibly inhibit an enzyme.

Question 37

PRACTICE QUESTION:
An alcoholic can be treated with Antabuse. This drug causes the accumulation of acetaldehyde, an alcohol byproduct, resulting in chest pains, headaches, vomiting, anxiety, and other symptoms, causing the patient to cease alcohol consumption. Acetaldehyde is normally degraded by the enzyme aldehyde oxidase. The Antabuse molecule resembles acetaldehyde. Use YOUR knowledge of enzymes to speculate as to how the drug may work.

Answer 37

This is a case of competitive inhibition. Antabuse replaces acetaldehyde at the enzyme’s active site preventing the enzyme from degrading its normal substrate. The buildup of acetaldehyde leads to unpleasant symptoms the more the person drinks alcohol.