8 Enzymes

Terms in this set (19)

OriginalAlphabetical

Look at the graph of reaction rate versus substrate concentration for an enzyme.
In which region does the reaction rate remain constant?

A
B
C

Region C

Refer again to the graph.
In which region is the enzyme saturated with substrate?
Hints

region A
region B
region C

Region C

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Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction?
Hints

Increase the pH.
Increase the temperature.
Increase the enzyme concentration.
Increase the substrate concentration.

Increase the enzyme concentration
—–
If an enzyme is saturated with substrate, and it is operating at optimum pH and optimum temperature, there is very little that can be done except to increase the enzyme concentration. Some enzymes can be activated further by allosteric activators, in which case one might add some activator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

1. A (n)______________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.
2. A (n)______________ inhibitor binds to a site on the enzyme that is not the active site.
3. Usually, a(n) _____________ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.
4. The competitive inhibitor competes with the substrate for the ______________ on the enzyme.
5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the ______________ is distorted.
6. Enzyme inhibitors disrupt normal interactions between an enzyme and its ______________.

1. competitive
2. noncompetitive
3. irreversible
4. active site
5. enzyme
6. substrate

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

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

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).

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?

Add more inhibitor to speed up the reaction.
Add more substrate; it will outcompete the inhibitor and increase the reaction rate.
Increase the temperature.
Increase the pH.

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

Rank these by reaction rate, as measured by the rate of product formation per unit time, from lowest reaction rate to highest reaction rate. To rank items as equivalent, overlap them.

Order:
-reaction catalyzed by enzyme A
-reaction catalyzed by enzyme B
-uncatalyzed reaction

lowest reaction rate
uncatalyzed reaction
reaction catalyzed by enzyme A
reaction catalyzed by enzyme B
highest reaction rate
——–
Correct
Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzed reaction, and it forms products more rapidly than an uncatalyzed reaction.

1. An enzyme is _____________ when it loses its native conformation and its biological activity.
2. An enzyme is considered a _____________ because it speeds up chemical reactions without being used up.
3. An enzyme is considered _____________ because of its ability to recognize the shape of a particular molecule.
4. A _____________, such as a vitamin, binds to an enzyme and plays a role in catalysis.
5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) _____________.
6. A substrate binds to an enzyme at the _____________, where the reaction occurs.
7. In a catalyzed reaction a reactant is often called a _____________.

1. Denatured
2. Catalyst
3. Specific
4. Cofactor
5. Complex
6. Active site
7. Substrate

A substrate binds at an enzyme’s active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis to proceed. An enzyme will denature, or change its shape and lose its biological activity, at too high a temperature or at a pH outside the enzyme’s optimal range.

…

In general, enzymes are what kinds of molecules?

carbohydrates
lipids
minerals
nucleic acids
proteins

Proteins

Enzymes work by _____.

reducing EA
adding energy to a reaction
decreasing the potential energy difference between reactant and product
adding a phosphate group to a reactant
increasing the potential energy difference between reactant and product

Reducing EA

An enzyme _____.

is a inorganic catalyst
is a source of energy for endergonic reactions
increases the EA of a reaction
can bind to nearly any molecule
is an organic catalyst

is an organic catalyst

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What name is given to the reactants in an enzymatically catalyzed reaction?

reactors
products
active sites
EA
substrate

substrate

As a result of its involvement in a reaction, an enzyme _____.

is used up
loses a phosphate group
loses energy
permanently alters its shape.
is unchanged

is unchanged

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?
Hints

P0 binds E4 and activates it.
P2 binds E2 and activates it.
P4 binds E1 and deactivates it.
P3 binds E2 and activates it
P4 binds E3 and deactivates it.

P4 binds E1 and deactivates it.
—–
Many enzymatic pathways are regulated by the feedback inhibition model described here. In fact, it is so common that another name for it is end-product inhibition.

How does an enzyme increase the rate of the chemical reaction it catalyzes?

An enzyme reduces the free-energy change (ΔG) of the reaction it catalyzes.
An enzyme’s active site binds only the reactants, and not the products of a reaction, pushing the equilibrium for the reaction far to the right.
An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.

An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.
—-
An enzyme catalyzes a reaction by lowering EA, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. Read about enzymes and activation energy.

Which statement about the binding of enzymes and substrates is correct?

Substrate molecules fit into the active site of an enzyme like a key fits into a lock.
Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction.
When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.

When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.
—-
As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate’s chemical groups and chemical groups on the side chains of the amino acids that form the active site. This shape change makes the active site fit even more snugly around the substrate. This induced fit is like a clasping handshake.

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to

add more of the enzyme.
add more substrate.
add a noncompetitive inhibitor.
add an allosteric inhibitor.
heat the solution to 90°C.

add more of the enzyme

Some bacteria are metabolically active in hot springs because

high temperatures make catalysis unnecessary.
their enzymes have high optimal temperatures.
their enzymes are completely insensitive to temperature.
they are able to maintain a lower internal temperature.
they use molecules other than proteins or RNAs as their main catalysts.

their enzymes have high optimal temperatures.