Chapter 6 Review Quiz

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. Most enzymes function within a narrow range of pH. Many have a closely defined optimum pH. Enzymes which function in the stomach usually have lower pH optima than those which are found in the intestine. Enzymes could be expected to be sensitive to minor pH changes because:

At very high pH, enzymes are destroyed correct incorrect

There are no physiological buffers which can withstand enzyme activity, so special proteins are needed in order to dilute the effects of strong acids and bases correct incorrect

Acids have no effect on enzymes correct incorrect

There are no organic acids or bases correct incorrect

Changes in proton concentrations result in changes in charges of acidic or basic groups, resulting in changes in the enzyme structure correct incorrect

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. Some very powerful digestive enzymes are produced as inactive zymogens in the pancreas and transported to the intestines, where they are activated by removal of a protein "keeper." These enzymes then act during digestion, and also act on other zymogens, activating them. Occasionally, an infection or injury to the pancreas causes these enzymes to become chemically activated within the pancreas. Under these conditions:

Digestion in the intestine would proceed faster than normal correct incorrect

Fats would be absorbed more rapidly than normal correct incorrect

The liver would require less energy supply than normal correct incorrect

The patient would probably notice no differences in his or her well being correct incorrect

The pancreas would become inflamed and severe pain would result correct incorrect

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. 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?

There are too many bacteria, and some consume the sulfa drugs and die, leaving the remaining bacteria to overwhelm the host correct incorrect

Humans don't make folic acid (it=s a vitamin for us) anyway, so the sulfa drugs usually don=t harm humans correct incorrect

Humans don't metabolize folic acid correct incorrect

Humans don't metabolize sulfa drugs correct incorrect

Humans can take extra folic acid to compensate for the sulfa drugs correct incorrect

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. Enzymes have a distinct advantage over non-biological catalysts because they:

Are made of protein correct incorrect

Are very efficient, specific, and sensitive to control correct incorrect

Are all allosteric correct incorrect

Can only be described by Lineweaver-Burk plots correct incorrect

Can not be denatured by heating correct incorrect

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. In a Lineweaver-Burk plot of enzyme activity, the highest values of [S] and Km are found:

Near the origin correct incorrect

At the top of the vertical axis correct incorrect

At the right end of the horizontal axis correct incorrect

At the left end of the horizontal axis correct incorrect

At the horizontal intercept of the curve correct incorrect

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. Most synthetic reactions in which carbon dioxide is used require the vitamin biotin. The biotin becomes covalently bound to a lysine molecule which is part of an enzyme, and the biotin can then attach to and carry the carbon dioxide molecule. Biotin is best referred to as a/an:

Coenzyme correct incorrect

Enzyme inhibitor correct incorrect

Competitive inhibitor correct incorrect

Organic acid correct incorrect

Enzyme correct incorrect

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. The fact that allosteric enzymes are remarkably sensitive to control makes them ideal candidates for:

The reverse of regulatory steps in a pathway correct incorrect

The rate-limiting steps in a pathway correct incorrect

The final steps in a pathway correct incorrect

All the steps in a pathway correct incorrect

Alternative pathways correct incorrect

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. If you wanted to explain the concept of Km to someone who didn't know as much about biochemistry as you, you might say that:

Km is not really a useful concept for biochemists correct incorrect

Km is a measure of how badly the enzyme reacts in the presence of other enzymes correct incorrect

Km is the substrate concentration which allows the reaction to proceed at half the maximum velocity correct incorrect

Km is only useful when considering noncompetitive inhibitors; competitive inhibitors don't have Km values correct incorrect

Km is the reciprocal of the intercept on the vertical axis of a Lineweaver-Burk plot correct incorrect

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. 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:

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

To allow the ethanol to act as a noncompetitive inhibitor of the metabolism of methanol correct incorrect

To make the patient forget about the pain so that the operation could proceed correct incorrect

To deaden the tissues to pain correct incorrect

To dissolve the methanol and move it through the circulation faster correct incorrect

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. Most coenzymes may be included in classes of foodstuffs known as:

Minerals correct incorrect

Carbohydrates correct incorrect

Fats correct incorrect

Vitamins correct incorrect

Metallic ions correct incorrect

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. The major effect of a catalyst on a reaction is to:

Keep the substrates apart correct incorrect

Lower the equilibrium constant correct incorrect

Raise the equilibrium constant correct incorrect

Raise the activation energy correct incorrect

Lower the activation energy correct incorrect

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. It is more useful for biochemists to know the specific activity of an enzyme than the activity of the enzyme because:

High levels of activity indicate very busy enzymes correct incorrect

Specific activity tells us exactly which reaction is being catalyzed and results in more positive identification of enzymes correct incorrect

Biochemistry is a very specialized field correct incorrect

Enzyme activation is brought about only under specialized conditions correct incorrect

Specific activity is a measure of the purity of the enzyme preparation correct incorrect

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. An enzyme in liver which removes glucose from blood has a high Km; another which does the same thing in brain tissue has a small Km. The usefulness of these two different values is that:

The enzyme in brain tissue can take glucose from the blood stream even when levels are low, and the enzyme in liver will not take glucose from blood unless levels are high correct incorrect

The enzyme in brain tissue can take glucose from the blood stream only when levels are high, and the enzyme in liver will not take glucose from blood unless levels are low correct incorrect

The enzyme in brain tissue can take glucose from the blood stream only when levels are high, and the enzyme in liver will not take glucose from blood at any time correct incorrect

This phenomenon is of no apparent value to the organism correct incorrect

It is actually dangerous for the organism; ideally, both Km=s should be high correct incorrect

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. A molecule of an enzyme which has a high turnover number:

Can easily be denatured correct incorrect

Can easily be replaced with another enzyme correct incorrect

Needs a constant supply of cofactors correct incorrect

Converts substrate to product very rapidly correct incorrect

Can be easily controlled correct incorrect

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. Most amino acids found in living things are L-form amino acids. A few amino acids found in antibiotics are D-form. The enzyme which converts D-alanine to L-alanine is best classified as an:

Transferase correct incorrect

Hydrolase correct incorrect

Lyase correct incorrect

Isomerase correct incorrect

Ligase correct incorrect

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. In addition to activation and inhibition, enzymes may be controlled by

Polymerization, hydrolysis, and esterification correct incorrect

Hydrolysis, esterification, and compartmentation correct incorrect

Esterification, compartmentation, and induction correct incorrect

Compartmentation, induction, and covalent modification correct incorrect

Induction, covalent modification, and polymerization correct incorrect

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. Consider the reaction: ethyl acetate + H₂OC> ethanol + acetic acid The enzyme which catalyzes this reaction is classified as a/an:

Oxidoreductase correct incorrect

Transferase correct incorrect

Hydrolase correct incorrect

Lyase correct incorrect

Isomerase correct incorrect

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. One way to tell whether an enzymatic reaction is carried out by an oxidoreductase is to:

Examine the substrate and products for loss or gain of hydrogen atoms correct incorrect

Examine the substrate to determine whether oxygen is present correct incorrect

Watch for flames to develop in the reaction bath correct incorrect

Note the increasing temperature of the reaction solution correct incorrect

Note any changes of color in the solution correct incorrect

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. Parkinson's disease is caused by a deficiency of dopamine in the substantia nigra of the brain. Dopamine is produced in the brain from L-DOPA (L-dihydroxyphenylalanine) by removal of a molecule of carbon dioxide. The L-DOPA is produced by oxidation of tyrosine, which is in turn produced from phenylalanine by another oxidoreductase. The enzyme which converts L-DOPA to dopamine is best classified as a/an:

Oxidoreductase correct incorrect

Transferase correct incorrect

Hydrolase correct incorrect

Lyase correct incorrect

Isomerase correct incorrect

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. 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:

The reaction runs out of substrate and substrate must be continually added in order to attain optimal activity correct incorrect

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

Enzymes can only function for a certain time period without resting correct incorrect

Substrates wear out after a certain time period correct incorrect

Heating darkens the solution, and the molecules need light in order to react correct incorrect

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. 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 a/an:

Transferase correct incorrect

Hydrolase correct incorrect

Lyase correct incorrect

Isomerase correct incorrect

Ligase correct incorrect

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. Melanin, the dark pigment in our hair and skin, is produced by a series of enzymatic reactions which start with phenylalanine. The phenylalanine is converted to tyrosine, then to L-DOPA, and finally though a series of steps to melanin and other substances. If the conversion of phenylalanine to tyrosine were blocked, the individual affected would probably:

Enjoy enhanced mental abilities correct incorrect

Be able to function in environments having low oxygen concentration correct incorrect

Have light-colored hair correct incorrect

Produce pleasant body odors correct incorrect

Have dark-colored hair correct incorrect