Chem 271 Ch. 6

Alcohol dehydrogenase without NAD+ is called a _______: A. Apoenzyme B. Holoenzyme C. Substrate D. Cofactor E. Coenzyme

A. Apoenzyme

Consider the following diagram. What constitutes the activation energy for the forward reaction? The reaction curve begins with A, travels horizontally then starts rising with B, peaks with C, passes D at the same level as A and ends at a lower level with E. A. C-A B. C-E C. E-A D. C-B E. E-D

A. C-A

Enzymes act by _________. A. Decreasing the energy of activation of a reaction B. Increasing the energy of activation of a reaction C. Raising the temperature of a reaction D. Providing a surface to favorably orient the reactants E. Both A and D are correct

A. Decreasing the energy of activation of a reaction

NADPH and NADH are coenzymes found in which class of enzymes? A. Dehydrogenases B. Ligases C. Hydrolases D. Transferases E. Both C and D are correct

A. Dehydrogenases

The synthesis of enzymes in response to changing metabolic needs is referred to as: A. Enzyme induction B. Allosteric regulation C. Negative feedback D. Zymogen activation E. Cooperative Binding

A. Enzyme induction

Which of the following amino acids is capable of acting as a general acid or general base at physiological pH ? A. Glycine B. Histidine C. Tyrosine D. Tryptophan E. Proline

B. Histidine

Which of the following classes of enzymes catalyze reactions involving the cleavage of bonds by the addition of water? A. Transferase B. Hydrolase C. Lyase D. Ligase E. Isomerase

B. Hydrolase

Metabolic flux is best defined as a: A. Lubrication enzyme that promotes the flow of reactants B. Rate of flow of metabolites from one point to another in a pathway C. Rate of a reaction D. Promoter molecule E. Both A and D are correct

B. Rate of flow of metabolites from one point to another in a pathway

Regulatory enzymes are a feature of what type of enzymatic control? A. Genetic control B. Covalent modification C. Allosteric regulation D. Compartmentation E. Both B and C are correct

C. Allosteric regulation

Consider the following reaction diagram. Which letter indicates the transition state? A. A B. B C. C D. D E. E

C. C

In the Lineweaver-Burk double reciprocal plot the slope is equal to _____. A.1/[S] B. 1/V C. Km/Vmax D. 1 /Vmax E. -1/Km

C. Km/Vmax

Consider the following reaction data. Alanylanine + water ---> Alanine [alanylanine] [water] Rate 0.1 0.1 1x10-4 0.2 0.2 2x10-4 0.1 0.2 2x10-4 0.2 0.2 4x10-4 The reaction is ____ order overall. A. zerp B. First C. Second D. Third E. Fouth

C. Second

Specific activity is defined as A. Enzyme concentration that converts 1 m mole of substrate to product per minute. B. Enzyme concentration that converts 1 mole of substrate to product per minute C. The number of I.U. per mg of protein D. The number of I. U. per gram of protein E. Enzyme concentration that converts 1 mm of substrate to product per minute.

C. The number of I.U. per mg of protein

Segregation of biochemical pathways into different organelles in an example of which type of enzymatic regulation? A. Genetic control B. Covalent modification C. Allosteric regulation D. Compartmentation E. Both B and C are correct

D. Compartmentation

Which of the following amino acids cannot actively participate in a catalytic site? A. Serine B. Threonine C. Tyrosine D. Glycine E. Glutamine

D. Glycine

Hexokinase is an example of which class of enzymes? A. Hydrolase B. Lyase C. Isomerase D. Transferase E. Ligase

D. Transferase

Which of the following is a feature of transition metals that makes them efficient cofactors? A. Have a high concentration of positive charge B. Can act as a Lewis acid C. Have directed valences D. Can exist as a variety of valence states E. All of the above are correct.

E. All of the above are correct.

Which of the following is not a property of enzymes? A. Capable of being regulated B. Reaction rates high in comparison to uncatalyzed reaction C. Highly specific D. Side products of reactions are rare E. All of the above are true

E. All of the above are true

Which of the following is not a type of oxidoreductase? A.Peroxidase B. Hydroxylase C. Reductase D. Dehydrogenase E. Peptidase

E. Peptidase

Which of the following is not present in the active site of alcohol dehydrogenase? A. Zn++ B. Histidine C. Cysteine D. NAD+ E. Proline

E. Proline

Most synthetic reactions in which carbon dioxide is used require the vitamin biotin. The biotin becomes covalently bound to a lysine molecule that is part of an enzyme, and the biotin can then attach to and carry the carbon dioxide molecule. Biotin is best referred to as an: a. Coenzyme b. Enzyme inhibitor c. Competitive inhibitor d. Organic acid e. Enzyme

a. Coenzyme.

One way to tell whether an enzymatic reaction is carried out by an oxidoreductase is to: a. Examine the substrate and products for loss or gain of hydrogen atoms b. Examine the substrate to determine whether oxygen is present c. Watch for flames to develop in the reaction bath d. Note the increasing temperature of the reaction solution e. Note any changes of color in the solution

a. Examine the substrate and products for loss or gain of hydrogen atoms.

In a Lineweaver-Burk plot of enzyme activity, the highest values of [S] and Km are found: a. Near the origin b. At the top of the vertical axis c. At the right end of the horizontal axis d. At the left end of the horizontal axis e. At the horizontal intercept of the curve

a. Near the origin

An enzyme in liver that removes glucose from blood has a high Km; another that does the same thing in brain tissue has a small Km. The usefulness of these two different values is that: a. The enzyme in brain tissue can take glucose from the bloodstream even when levels are low, and the enzyme in liver will not take glucose from blood unless levels are high b. The enzyme in brain tissue can take glucose from the bloodstream only when levels are high, and the enzyme in liver will not take glucose from blood unless levels are low c. The enzyme in brain tissue can take glucose from the bloodstream only when levels are high, and the enzyme in liver will not take glucose from blood at any time d. This phenomenon is of no apparent value to the organism e. It is actually dangerous for the organism; ideally, both KmB s should be high

a. The enzyme in brain tissue can take glucose from the bloodstream even when levels are low, and the enzyme in liver will not take glucose from blood unless levels are high.

Methanol is a very poisonous substance, accounting for a number of deaths and many cases of blindness yearly. While the methanol itself is sometimes not toxic, it may be metabolized by the liver to more toxic molecules such as formic acid or formaldehyde. Before more efficacious treatments were developed, a person who had ingested methanol was often given a large amount of ethanol orally. The purpose of this treatment was: a. To allow the ethanol to act as a competitive inhibitor of the metabolism of methanol b. To allow the ethanol to act as a noncompetitive inhibitor of the metabolism of methanol c. To make the patient forget about the pain so that the operation could proceed d. To deaden the tissues to pain e. To dissolve the methanol and move it through the circulation faster

a. To allow the ethanol to act as a competitive inhibitor of the metabolism of methanol.

Enzymes have a distinct advantage over nonbiological catalysts because they: a. Are made of protein b. Are very efficient, specific, and sensitive to control c. Are all allosteric d. Can only be described by Lineweaver-Burk plots e. Can not be denatured by heating

b. Are very efficient, specific, and sensitive to control.

Most growing cells require folic acid. Bacteria synthesize their folic acid from a number of materials, including para-aminobenzoic acid. We slow bacterial growth by treating infections in humans with sulfa drugs. (The sulfa drugs are very similar to para-aminobenzoic acid and act as competitive inhibitors, keeping the bacteria from synthesizing folic acid.) If the sulfa drugs kill bacteria, why don"t they harm the human, too? a. There are too many bacteria, and some consume the sulfa drugs and die, leaving the remaining bacteria to overwhelm the host b. Humans donB t make folic acid (itB s a vitamin for us) anyway, so the sulfa drugs usually donB t harm humans c. Humans donB t metabolize folic acid d. Humans donB t metabolize sulfa drugs e. Humans can take extra folic acid to compensate for the sulfa drugs

b. Humans donB t make folic acid (itB s a vitamin for us) anyway, so the sulfa drugs usually donB t harm humans.

As a solution containing an enzymatic reaction is heated, the temperature rises and the reaction velocity rises gradually for some period but typically falls off very rapidly after reaching the optimum temperature because: a. The reaction runs out of substrate and substrate must be continually added to attain optimal activity b. The enzyme functions more rapidly as the solution is heated because the molecules move faster, but after a certain temperature, the enzyme becomes denatured c. Enzymes can only function for a certain time period without resting d. Substrates wear out after a certain time period e. Heating darkens the solution, and the molecules need light to react

b. The enzyme functions more rapidly as the solution is heated because the molecules move faster, but after a certain temperature, the enzyme becomes denatured.

The fact that allosteric enzymes are remarkably sensitive to control makes them ideal candidates for: a. The reverse of regulatory steps in a pathway b. The rate-limiting steps in a pathway c. The final steps in a pathway d. All the steps in a pathway e. Alternative pathways

b. The rate-limiting steps in a pathway.

Melanin, the dark pigment in our hair and skin, is produced by a series of enzymatic reactions that start with phenylalanine. The phenylalanine is converted to tyrosine, then to ι-DOPA, and finally through a series of steps to melanin and other substances. If the conversion of phenylalanine to tyrosine were blocked, the individual affected would probably: a. Enjoy enhanced mental abilities b. Be able to function in environments having low oxygen concentration c. Have light-colored hair d. Produce pleasant body odors e. Have dark-colored hair

c. Have light-colored hair.

Consider the reaction: thyl acetate + H2O C> ethanol + acetic acid. The enzyme which catalyzes this reaction is classified as an: a. Oxidoreductase b. Transferase c. Hydrolase d. Lyase e. Isomerase

c. Hydrolase.

If you wanted to explain the concept of Km to someone who didnB t know as much about biochemistry as you, you might say that: a. Km is not really a useful concept for biochemists b. Km is a measure of how badly the enzyme reacts in the presence of other enzymes c. Km is the substrate concentration that allows the reaction to proceed at half the maximum velocity d. Km is only useful when considering noncompetitive inhibitors; competitive inhibitors donB t have Km values e. Km is the reciprocal of the intercept on the vertical axis of a Lineweaver-Burk plot

c. Km is the substrate concentration that allows the reaction to proceed at half the maximum velocity.

In addition to activation and inhibition, enzymes may be controlled by: a. Polymerization, hydrolysis, and esterification b. Hydrolysis, esterification, and compartmentation c. Esterification, compartmentation, and induction d. Compartmentation, induction, and covalent modification e. Induction, covalent modification, and polymerization

d. Compartmentation, induction, and covalent modification.

A molecule of an enzyme that has a high turnover number: a. Can easily be denatured b. Can easily be replaced with another enzyme c. Needs a constant supply of cofactors d. Converts substrate to product very rapidly e. Can be easily controlled

d. Converts substrate to product very rapidly.

Most amino acids found in living things are ι-form amino acids. A few amino acids found in antibiotics are D-form. The enzyme that converts D-alanine to ι-alanine is best classified as an: a. Transferase b. Hydrolase c. Lyase d. Isomerase e. Ligase

d. Isomerase.

Parkinson"s disease is caused by a deficiency of dopamine in the substantia nigra of the brain. Dopamine is produced in the brain from ι-DOPA (ι-dihydroxyphenylalanine) by removal of a molecule of carbon dioxide. The ι-DOPA is produced by oxidation of tyrosine, which is in turn produced from phenylalanine by another oxidoreductase. The enzyme that converts ι-DOPA to dopamine is best classified as an: a. Oxidoreductase b. Transferase c. Hydrolase d. Lyase e. Isomerase

d. Lyase.

Most coenzymes may be included in classes of foodstuffs known as: a. Minerals b. Carbohydrates c. Fats d. Vitamins e. Metallic ions

d. Vitamins.

During replication, a number of DNA fragments are produced. Energy is required for an enzyme to join these fragments together to form an intact strand of DNA. The enzyme is classified as an): a. Transferase b. Hydrolase c. Lyase d. Isomerase e. Ligase

e. Ligase

The major effect of a catalyst on a reaction is to: a. Keep the substrates apart b. Lower the equilibrium constant c. Raise the equilibrium constant d. Raise the activation energy e. Lower the activation energy

e. Lower the activation energy.

It is more useful for biochemists to know the specific activity of an enzyme than the activity of the enzyme because: a. High levels of activity indicate very busy enzymes b. Specific activity tells us exactly which reaction is being catalyzed and results in more positive identification of enzymes c. Biochemistry is a very specialized field d. Enzyme activation is brought about only under specialized conditions e. Specific activity is a measure of the purity of the enzyme preparation

e. Specific activity is a measure of the purity of the enzyme preparation.