Mastering Biology: Chapter 6 Enzymes

**The 4 ways that enzymes can lower activation energy

-Orienting substrates correctly -Straining substrate bonds -Providing a favorable microenvironment -Covalently bonding to the substrate

(See MB question #6)

-reaction rate is constant where it levels off at the end (c) -this is also where the enzyme is saturated with substrate (c)

Which statement about the binding of enzymes and substrates is correct? When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape. 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

(See mastering biology for question 3)

activation energy: c

A substrate binds to an enzyme at the ______, where the reaction occurs

active site

Cooperativity is a form of allosteric activation in which the product of a metabolic pathway serves as a competitive inhibitor of an early enzyme in the pathway. binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits. all of the enzymes in a metabolic pathway are contained within a single multienzyme complex. completion of one step in a metabolic pathway is required before a subsequent step can occur.

binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits

The active site of an enzyme is the region that binds substrates for the enzyme. binds allosteric regulators of the enzyme. is inhibited by the presence of a coenzyme or a cofactor. binds noncompetitive inhibitors of the enzyme.

binds substrates for the enzyme

An enzyme is considered a _____ because it speeds up chemical reactions without being used up

catalyst

A noncompetitive inhibitor decreases the rate of an enzymatic reaction by changing the G for the reaction. changing the shape of the enzyme active site. binding to the active site of the enzyme. decreasing the activation energy required for the reaction.

changing the shape for the enzyme active site

A ______, such as a vitamin, binds to an enzyme and plays a role in catalysis

cofactor

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n) competitive inhibitor of the enzyme. noncompetitive inhibitor of the enzyme. allosteric activator of the enzyme. coenzyme derived from a vitamin. cofactor necessary for enzyme activity.

cofactor necessary for enzyme activity

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? denaturation of the enzyme competitive inhibition allosteric inhibition saturation of the enzyme activity

competitive inhibition

When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) ______

complex

An enzyme is ____ when it loses its native conformation and its biological activity

denatured

The mechanism by which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as irreversible inhibition. noncooperative inhibition. feedback inhibition. metabolic inhibition.

feedback 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 reduces the free energy of activation (EA) 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

What will happen to the rates of the forward and reverse reactions when a catalyst is added? Forward rate increases; reverse rate decreases. Both forward and reverse rates increase. Both forward and reverse rates decrease. Forward rate decreases; reverse rate increases.

Both forward and reverse rates increase

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

Increase the enzyme concentration

In the figure, why does the reaction rate plateau at higher reactant concentrations? -Most enzyme molecules are occupied by substrate at high reactant concentrations. -The reaction nears equilibrium at high reactant concentrations. -The activation energy for the reaction increases with reactant concentration. -Feedback inhibition by product occurs at high reactant concentrations. -The rate of the reverse reaction increases with reactant concentration.

Most enzyme molecules are occupied by substrate at high reactant concentrations.

Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes? The binding of two substrates in the active site provides the correct orientation for them to react to form a product. The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction. The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction. Binding of the substrate to the active site can stretch bonds in the substrate that need to be broken. The active site can provide heat from the environment that raises the energy content of the substrate.

The active site can provide heat from the environment that raises the energy content of the substrate.

Which of the following statements about feedback regulation of a metabolic pathway is correct? The final product of a metabolic pathway is usually the compound that regulates the pathway. The compound that regulates the pathway acts as a competitive inhibitor or a positive allosteric regulator. The products of the pathway become the reactants for a different reaction, and thus products are unable to accumulate. The enzyme that is regulated by feedback inhibition is usually the last enzyme in the metabolic pathway. Accumulation of the product of the pathway increases further formation of that product.

The final product of a metabolic pathway is usually the compound that regulates the pathway.

The Haber process is typically carried out at a temperature of approximately 500∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C?

The reaction rate would decrease

N2(g)+3H2(g)⇌2NH3(g) What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased?

The reaction rate would decrease; as nitrogen decreases, collisions between N & H are less likely to occur

Enzymes are described as catalysts, which means that they __________. increase the rate of a reaction without being consumed by the reaction provide activation energy for the reactions they facilitate are proteins increase the free energy of the reactants to make the reaction go faster can alter the free energy change (ΔG) for a chemical reaction

increase the rate of a reaction without being consumed by the reaction

Ammonia, NH3, is used in numerous industrial processes, including the production of pharmaceuticals such as sulfonamide and antimalarials and vitamins such as the B vitamins. The equilibrium equation for the synthesis of ammonia (sometimes known as the Haber process) is N2(g)+3H2(g)⇌2NH3(g) Which of the following would increase the rate of the reverse reaction? increasing the concentration of ammonia decreasing the temperature increasing the concentration of nitrogen

increasing the concentration of ammonia

A mutation that results in a single amino acid substitution in a region of the enzyme outside of the active site will almost always destroy the activity of the enzyme. will often change the substrate specificity of the enzyme. may alter the optimal pH for the enzyme. may alter the ability of a competitive inhibitor to bind to the enzyme.

may alter the optimal pH for the enzyme

An enzyme is considered _____ because of its ability to recognize the shape of a particular molecule

specific

(See mastering biology for question 2)

stomach: 1 & 4

In a catalyzed reaction a reactant is often called a ______

substrate