Enzymes

Which of the following statements is true of enzyme catalysts?

A.They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates.

B. They lower the free energy of the reaction

C. They increase the equilibrium constant for a reaction, thus favoring product formation.

D. They lower the free energy of the transition state

E. They specifically bind to substrates, but are never covalently attached to substrate or product.

Which of the following are typical characteristics of enzymes:

A. Enzymes act on only one substrate molecule

B. Enzymes are highly specific.

C. Enzymes are usually highly regulated

D. Enzymes alter the equilibrium of a reaction

E. Enzymes increase the rate of reactions much more than non-enzyme catalysts for the same type of reaction.

Enzymes act as catalysts because:

A. they are not altered by the reaction catalysed

B. their active sites are complementary to the substrate of the reaction

C. they do not change the position of a thermodynamic quilibrium

D. they are specific for only one substrate

E. they bind the transition state of the reaction catalysed

If the pKa of the histidine is known to be 6.5 in the active site and the pH of maximum catalytic activity is 7.2, what is likely the primary role of histidine in the catalytic reaction?

A. acts as a proton donor

B. forms a covalent bond with the substrate

C. stabilizes a charged intermediate

D. reduces the entropy of the substrate

Allosteric enzymes:

A. depend mainly upon covalent modification of the enzyme

B. bind ligands reversibly

C. have a Km that is 1/3 Vmax

D. usually show strict Michaelis-Menten kinetics.

E. have a Vmax that depends only on substrate concentration

True or False

An enzyme can only use one substrate at a time

When a non-protein factor is needed for an enzyme to work, and the factor is not bound, the enzyme is known as:

A. A holoenzyme

B. An apoenzyme

C. An allosteric enzyme

D. A unconjugated enzyme

When a non-protein factor is needed for an enzyme to work, and the factor is bound, the enzyme is known as:

A. A holoenzyme

B. An apoenzyme

C. An allosteric enzyme

D. A unconjugated enzyme

Why is it important that the enzymes in lysosomes are more active at acidic pH than at neutral pH?

A. The pH dependence allows for minimum efficiency for the digestion of food

B. It prevents their diffusion out of the lysosomes.

C. It maximizes the interaction with their substrates which are always bases.

D. It prevents them from accidentally degrading the macromolecules in the cytosol.

E. It allows for regulation of their uptake by the mitochondria.

When no other non-protein factor is needed for an enzyme to work then the enzyme is known as:

A. A Holoenzyme

B. Unconjugated

C. An Apoenzyme

D. Conjugated

Allosteric modulators seldom resemble the substrate or product of the enzyme. What does this observation show?

A. Modulators likely bind at a site other than the active site.

B. Modulators always act as activators.

C. Modulators bind non-covalently to the enzyme.

D. The enzyme catalyzes more than one reaction

An enzyme that catalyzes conversions of L-sugars to D-sugars is called a/an ________.

A. lyase

B. hydrolase

C. synthetase

D. synthase

E. isomerase

The release of free energy as a result of the interaction between enzyme and substrate is sometimes called the binding energy. Which of the following is true of the binding energy derived from enzyme-substrate interactions?

A. Most of it is used for enzyme stability

B. Most of it is derived from covalent bonds between enzyme and substrate.

C. It is sometimes used to hold two substrates in the optimal orientation for reaction.

D. It is the difference in initial and final free energy between reactants and products.

E. It is used to provide more kinetic energy to the reactants

Chemical reactions in the absence of a catalyst may be distinguished from enzyme-catalysed reactions because:

A. enzyme-catalysed reactions produce a variety of products from a single substrate

B. enzyme-catalysed reactions are not first-order with respect to substrate concentration below the Km value

C. the free energy of activation is lower for an enzyme-catalysed reaction

D. chemical reactions are saturable with substrate

E. chemical reactions proceed at lower temperatures

True or False

Enzymes are not as efficient as most catalysts used in organic chemistry, since they must function at body temperature.

True or False

Enzymes increase the rates of both forward and reverse reactions but do not affect the equilibrium of chemical reactions.

The enzyme fumarase catalyzes the reversible hydration of fumaric acid to L-malate; however, the enzyme will not catalyze the hydration of maleic acid, the cis isomer of fumaric acid. This is an example of:

A. chiral activity.

B. stereospecificity.

C. racemization.

D. stereoisomerization.

E. biological activity.

Which of the following statements does not apply to the effect of temperature on an enyme-catalysed reaction?

A. At high temperatures the enzyme may be denatured

B. At low temperatures the rate doubles (approximately) for each 10°C rise

C. Denatured enzymes always regain their lost activity on cooling

D.Enzymes are inactivated both by being held for long periods of time at moderate temperatures and by being held for short periods of time at high temperatures

Which of the following potentially provide an answer to the question 'Why are enzymes so big?' when compared with small non-enzyme catalysts?

A. The large size of the enzyme forms a scaffold to optimally interact with the substrate.

B. The large size of the enzyme may protect it the active site from damage.

C. The large size of the enzyme may be involved in its regulation

D. The large size of the enzyme is needed to increase the activation energy of a reaction

Which are true about an enzyme catalase:

A. Catalase provides the energy to make the reaction proceed faster

B. Catalase can change the reaction mechanism

C. Catalyse alters the equilibrium in favour of the products.

D. Catalase reduces the free energy change (ΔG) for the activation of the reaction

E. Catalase is used up in the reactionF. Catalase reduces the free energy change (ΔG) for the reaction

Which of the following statements is true of enzyme catalysts?

A.They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates.

B. They lower the free energy of the reaction

C. They increase the equilibrium constant for a reaction, thus favoring product formation.

D. They lower the free energy of the transition state

E. They specifically bind to substrates, but are never covalently attached to substrate or product

When a non-protein factor is needed for an enzyme to work then the enzyme is known as:

A. Conjugated

B. Allosteric

C. Unconjugated

D. Non-allosteric

Oxidases, peroxidases, oxygenases or reductases are all:

A. lyases.

B. synthases.

C. synthetases.

D. oxidoreductases.

E. hydrolases.