Introduction to General, Organic and Biochemistry

Frederick A. Bettelheim, William H. Brown, Mary K. Campbell

Chapter 23 Enzymes - all with Video Answers

Educators

Chapter Questions

01:06

Problem 1

What is the difference between a catalyst and an enzyme?

Simon Sauvageau

Numerade Educator

00:22

Problem 2

What are ribozymes made of?

Sabihah Khan

Numerade Educator

00:50

Problem 3

Would a lipase hydrolyze two triglycerides, one containing only oleic acid and the other containing only palmitic acid, with equal ease?

Simon Sauvageau

Numerade Educator

00:48

Problem 4

Compare the activation energy in uncatalyzed reactions and in enzyme-catalyzed reactions.

Simon Sauvageau

Numerade Educator

01:20

Problem 5

Why does the body need so many different enzymes?

Simon Sauvageau

Numerade Educator

02:11

Trypsin catalyzes the hydrolysis of polypeptide chains at the carboxyl side of a lysine or arginine residue (Figure 23 -1). Chymotrypsin cleaves polypeptide chains on the carboxyl side of an aromatic amino acid residue or any other nonpolar, bulky side chain. Which enzyme is more specific? Explain.

Sandra Lundell

Numerade Educator

03:58

Problem 7

Both lyases and hydrolases catalyze reactions involving water molecules. What is the difference in the types of reactions that these two enzymes catalyze?

Sandra Lundell

Numerade Educator

04:37

Problem 8

Monoamine oxidases are important enzymes in brain chemistry. Judging from the name, which of the following would be a suitable substrate for this class of enzymes:

Sandra Lundell

Numerade Educator

01:46

Problem 9

On the basis of the classification given in Section $23-2,$ decide to which group each of the following enzymes belongs:
(a) Phosphoglyceromutase
(b) Urease
(c) Succinate dehydrogenase
(d) Aspartase

Rabeya Zahid

Numerade Educator

01:31

Problem 10

What kind of reaction does each of the following enzymes catalyze?
(a) Deaminases
(b) Hydrolases
(c) Dehydrogenases
(d) Isomerases

Simon Sauvageau

Numerade Educator

01:49

Problem 11

What is the difference between a coenzyme and a cofactor?

Rabeya Zahid

Numerade Educator

01:39

Problem 12

In the citric acid cycle, an enzyme converts succinate to fumarate (see the reaction in Problem 23 - 9 c) . The enzyme consists of a protein portion and an organic molecule portion called FAD. What terms do we use to refer to (a) the protein portion and (b) the organic molecule portion?

Rabeya Zahid

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01:58

Problem 13

What is the difference between reversible and irreversible noncompetitive inhibition?

Simon Sauvageau

Numerade Educator

02:12

Problem 14

In most enzyme-catalyzed reactions, the rate of reaction reaches a constant value with increasing substrate concentration. This relationship is described in a saturation curve diagram (Figure $23-4$ ). If the enzyme concentration on a molar basis is twice the maximum substrate concentration, would you obtain a saturation curve?

Sandra Lundell

Numerade Educator

01:14

Problem 15

At a very low concentration of a certain substrate, we find that when the substrate concentration doubles, the rate of the enzyme-catalyzed reaction also doubles. Would you expect the same finding at a very high substrate concentration? Explain.

Simon Sauvageau

Numerade Educator

01:10

Problem 16

If we wish to double the rate of an enzyme-catalyzed reaction, can we do so by increasing the temperature by $10^{\circ} \mathrm{C} ?$ Explain.

Simon Sauvageau

Numerade Educator

01:17

Problem 17

A bacterial enzyme has the following temperaturedependent activity.
(a) Is this enzyme more or less active at normal body temperature than when a person has a fever?
(b) What happens to the enzyme activity if the patient's temperature is lowered to $35^{\circ} \mathrm{C} ?$

Rabeya Zahid

Numerade Educator

01:59

Problem 18

The optimal temperature for the action of lactate dehydrogenase is $36^{\circ} \mathrm{C} .$ It is irreversibly inactivated at $85^{\circ} \mathrm{C},$ but a yeast containing this enzyme can survive for months at $-10^{\circ} \mathrm{C}$. Explain how this can happen.

Sandra Lundell

Numerade Educator

03:03

Problem 19

The activity of pepsin was measured at various pH values. When the temperature and the concentrations of pepsin and substrate were held constant, the following activities were obtained:
$$\begin{array}{lc}
\text { pH } & \text { Activity } \\
1.0 & 0.5 \\
1.5 & 2.6 \\
2.0 & 4.8 \\
3.0 & 2.0 \\
4.0 & 0.4 \\
5.0 & 0.0
\end{array}$$
(a) Plot the pH dependence of pepsin activity.
(b) What is the optimal pH?
(c) Predict the activity of pepsin in the blood at pH 7.4

Rabeya Zahid

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02:15

Problem 20

How can the pH profile of an enzyme tell you something about the reaction mechanism if you know the amino acids at the active site?

Sandra Lundell

Numerade Educator

04:53

Problem 21

Urease can catalyze the hydrolysis of urea but not the hydrolysis of diethylurea. Explain why diethylurea is not hydrolyzed.

Ronald Prasad

Numerade Educator

03:58

Problem 22

The following reaction may be represented by the cartoon figures:
Glucose $+\mathrm{ATP} \rightleftharpoons$ glucose 6 -phosphate $+\mathrm{ADP}$
In this enzyme-catalyzed reaction, $\mathrm{Mg}^{2+}$ is a cofactor, fluoroglucose is a competitive inhibitor, and $\mathrm{Cd}^{2+}$ is a noncompetitive inhibitor. Identify each component of the reaction by a cartoon figure and assemble them to show (a) the normal enzyme reaction, $(\mathrm{b})$ a competitive inhibition, and
(c) a noncompetitive inhibition.

Danielle Ashley

Numerade Educator

01:15

Problem 23

Which amino acids appear most frequently in the active sites of enzymes?

Sandra Lundell

Numerade Educator

01:15

Problem 24

What kind of chemical reaction occurs most frequently at the active site?

Sandra Lundell

Numerade Educator

00:56

Problem 25

Which of the following is a correct statement describing the induced-fit model of enzyme action? Substrates fit into the active site:
(a) because both are exactly the same size and shape.
(b) by changing their size and shape to match those of the active site.
(c) by changing the size and shape of the active site upon binding.

Simon Sauvageau

Numerade Educator

04:27

Problem 26

What is the maximum rate that can be achieved in competitive inhibition compared with noncompetitive inhibition?

Rabeya Zahid

Numerade Educator

00:51

Problem 27

Enzymes are long protein chains, usually containing more than 100 amino acid residues. Yet the active site contains only a few amino acids. Explain why the other amino acids of the chain are present and what would happen to the enzyme activity if the enzyme's structure were changed significantly.

Simon Sauvageau

Numerade Educator

04:26

Problem 28

On some baking product labels, you might see an ingredient called "invert sugar." This is made by hydrolyzing sucrose (common table sugar) to glucose and fructose. The reaction is catalyzed by the enzyme invertase. Using the following data, determine whether the inhibition by $2 \mathrm{M}$ urea is competitive or noncompetitive.
$$\begin{aligned}
&\begin{array}{lcc}
\begin{array}{l}
\text { Sucrose } \\
\text { Concentration (M) }
\end{array} & \begin{array}{c}
\text { Velocity } \\
\text { (arbitrary units) }
\end{array} & \begin{array}{c}
\text { Velocity + } \\
\text { Inhibitor }
\end{array} \\
0.0292 & 0.182 & 0.083 \\
0.0584 & 0.265 & 0.119 \\
0.0876 & 0.311 & 0.154 \\
0.117 & 0.330 & 0.167 \\
0.175 & 0.372 & 0.192
\end{array}
\end{aligned}$$

Sana Riaz

Numerade Educator

00:48

Problem 29

The hydrolysis of glycogen to yield glucose is catalyzed by the enzyme phosphorylase. Caffeine, which is not a carbohydrate and not a substrate for the enzyme, inhibits phosphorylase. What kind of regulatory mechanism is at work?

Rabeya Zahid

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01:06

Problem 30

Can the product of a reaction that is part of a sequence act as an inhibitor for another reaction in the sequence? Explain.

Rabeya Zahid

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01:15

Problem 31

What is the difference between a $z y$ mogen and a proenzyme?

Rabeya Zahid

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01:31

Problem 32

The enzyme trypsin is synthesized by the body in the form of a long polypeptide chain containing 235 amino acids (trypsinogen), from which a piece must be cut before the trypsin can be active. Why does the body not synthesize trypsin directly?

Simon Sauvageau

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01:14

Problem 33

Give the structure of a tyrosyl residue of an enzyme modified by a protein kinase.

Rabeya Zahid

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00:39

Problem 34

What is an isozyme?

Simon Sauvageau

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02:14

Problem 35

The enzyme glycogen phosphorylase initiates the phosphorolysis of glycogen to glucose 1-phosphate. The enzyme exists in two forms: phosphorylase $b$ is less active, and phosphorylase $a$ is more active. The difference between the $b$ and $a$ forms is the modification of the apoenzyme. Phosphorylase $a$ has two phosphate groups added to the polypeptide chain. In analogy with the pyruvate kinase discussed in the text, give a scheme indicating the transition between the $b$ and $a$ forms. Which enzymes and which cofactors control this reaction?

Rabeya Zahid

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01:12

Problem 36

How can you tell if an enzyme is allosteric by plotting velocity versus substrate?

Rabeya Zahid

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00:42

Problem 37

Explain the nature of the two types of control of glycogen phosphorylase. What is the advantage to having both control types?

Rabeya Zahid

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03:11

Problem 38

Which type of regulation discussed in Section $23-6$ is the least reversible? Explain.

Rabeya Zahid

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01:13

Problem 39

The enzyme phosphofructokinase (PFK) (Chapter 28 ) has two types of subunits, $M$ and $L$, for muscle and liver, respectively. These subunits combine to form a tetramer. How many isozymes of PFK exist? What are their designations?

Rabeya Zahid

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01:25

Problem 40

If you separated PFK using electrophoresis, how would the isozymes migrate if the M subunit has a lower pI than the L subunit?

Rabeya Zahid

Numerade Educator

00:32

Problem 41

After a heart attack, the levels of certain enzymes rise in the serum. Which enzyme would you monitor within 24 hours following a suspected heart attack?

Simon Sauvageau

Numerade Educator

00:53

Problem 42

The enzyme formerly known as GPT (glutamatepyruvate transaminase) has a new name: ALT (alanine aminotransferase). Looking at the equation in Section $28-9,$ which is catalyzed by this enzyme, what prompted this change of name?

Rabeya Zahid

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00:58

Problem 43

If an examination of a patient indicated elevated levels of AST but normal levels of ALT, what would be your tentative diagnosis?

Rabeya Zahid

Numerade Educator

01:49

Problem 44

Which LDH isozyme is monitored in the case of a heart attack?

Rabeya Zahid

Numerade Educator

00:47

Problem 45

Chemists who have been exposed for years to organic vapors usually show higher-than-normal activity when given the alkaline phosphatase test. Which organ in the body do organic vapors affect?

Rabeya Zahid

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01:33

Problem 46

Which enzyme preparation is given to patients after duodenal ulcer surgery?

Prashant Bana

Numerade Educator

03:26

Problem 47

Chymotrypsin is secreted by the pancreas and passed into the intestine. The optimal pH for this enzyme is $7.8 .$ If a patient's pancreas cannot manufacture chymotrypsin, would it be possible to supply it orally? What happens to chymotrypsin's activity during its passage through the gastrointestinal tract?

Noah Boudrie

Numerade Educator

00:54

Problem 48

Explain why transition-state analogs are potent inhibitors.

Rabeya Zahid

Numerade Educator

00:47

Problem 49

How do transition-state analogs relate to the idea of the induced-fit model of enzymes?

Rabeya Zahid

Numerade Educator

02:01

Problem 50

Explain the relationship between transition-state analogs and abzymes.

Rabeya Zahid

Numerade Educator

00:56

Problem 51

(Chemical Connections 23 A) Acetylcholine causes muscles to contract. Succinylcholine, a close relative, is a muscle relaxant. Explain the different effects of these related compounds.

Rabeya Zahid

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00:49

Problem 52

(Chemical Connections 23 A) An operating team usually administers succinylcholine before bronchoscopy. What is achieved by this procedure?

Rabeya Zahid

Numerade Educator

01:39

Problem 53

(Chemical Connections $23 \mathrm{B}$ ) PKM $\zeta$ is a type of enzyme called a kinase. Kinases are very important in metabolism. Look through the metabolism chapters (Chapters 27 and 28 ) and find two examples of kinases. What reactions do kinases catalyze?

Rabeya Zahid

Numerade Educator

01:50

Problem 54

(Chemical Connections $23 \mathrm{B}$ ) Explain how researchers used the drug ZIP to test its effect on long-term memory. How did they know that food aversion was a long-term memory phenomenon?

Rabeya Zahid

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00:43

Problem 55

(Chemical Connections 23 B) Why would researchers want to be able to selectively block long-term memory?

Rabeya Zahid

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01:48

Problem 56

(Chemical Connections $23 \mathrm{C}$ ) What role does $\mathrm{Mn}^{2+}$ play in anchoring the substrate in the active site of protein kinase?

Rabeya Zahid

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00:52

Problem 57

(Chemical Connections $23 \mathrm{C}$ ) Which amino acids of the active site interact with the $=\mathrm{CH}_{2}$ group of the phosphoenol pyruvate? Do these amino acids provide the same surface environment? What is the nature of the interaction?

Rabeya Zahid

Numerade Educator

00:49

Problem 58

(Chemical Connections 23 D) What is the strategy in drug design to fight AIDS?

Rabeya Zahid

Numerade Educator

00:47

Problem 59

(Chemical Connections 23 D) Why did scientists want to create a drug to inhibit cGMP diesterases?

Rabeya Zahid

Numerade Educator

00:39

Problem 60

(Chemical Connections 23 D) How can the crystal structures of enzymes be used in drug design?

Rabeya Zahid

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02:35

Problem 61

(Chemical Connections 23 D) Would reducing the population of intestinal bacteria be a useful way to alleviate the side effects of treatment for colon cancer?

Rabeya Zahid

Numerade Educator

01:03

Problem 62

(Chemical Connections $23 \mathrm{E}$ ) How does feedback inhibition play a role in the activity of phosphofructokinase?

Rabeya Zahid

Numerade Educator

01:02

Problem 63

(Chemical Connections $23 \mathrm{E}$ ) What is the relationship between protein modification and allosteric control of phosphofructokinase?

Rabeya Zahid

Numerade Educator

01:32

Problem 64

(Chemical Connections $23 \mathrm{F}$ ) Can the functional groups in the side chains of enzymes serve as nucleophiles or not? Give an example to support your answer

Rabeya Zahid

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00:35

Problem 65

(Chemical Connections $23 \mathrm{F}$ ) Can the functional groups in the side chains of enzymes participate in acid-base catalysis? Give an example to support your answer.

Rabeya Zahid

Numerade Educator

00:35

Problem 65

(Chemical Connections $23 \mathrm{F}$ ) Can the functional groups in the side chains of enzymes participate in acid-base catalysis? Give an example to support your answer.

Rabeya Zahid

Numerade Educator

00:53

Problem 66

(Chemical Connections $23 \mathrm{F}$ ) One of the requirements for a substance to be considered a catalyst is that it is regenerated in its original form. Do enzymes fulfill this requirement?

Rabeya Zahid

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00:28

Problem 67

Is it possible to produce an abzyme that will hydrolyze the coat protein of a virus?

Rabeya Zahid

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01:19

Problem 68

How would the binding of HIV to a cell be affected if the coat protein gp120 is damaged?

Rabeya Zahid

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00:40

Problem 69

Is it possible for an abzyme to affect more than one virus particle?

Rabeya Zahid

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01:13

Problem 70

Where can one find enzymes that are both stable and active at $90^{\circ} \mathrm{C} ?$

Rabeya Zahid

Numerade Educator

02:10

Problem 71

Food can be preserved by inactivation of enzymes that would cause spoilage- for example, by refrigeration. Give an example of food preservation in which the enzymes are inactivated (a) by heat and (b) by lowering the pH.

Prashant Bana

Numerade Educator

01:05

Problem 72

Enzyme therapy (administration of digestive enzymes) is suggested as a treatment for various medical conditions, including autism. How likely is it that this method will be effective?

Rabeya Zahid

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00:38

Problem 73

Would you expect to find active digestive enzymes in a cooked hot dog? What is the reason for your answer?

Rabeya Zahid

Numerade Educator

01:29

Problem 74

Why is enzyme activity during myocardial infarction measured in patients' serum rather than in his or her urine?

Rabeya Zahid

Numerade Educator

00:41

Problem 75

What is the common characteristic of the amino acids of which the carboxyl groups of the peptide bonds can be hydrolyzed by trypsin?

Rabeya Zahid

Numerade Educator

00:51

Problem 76

Many enzymes are active only in the presence of $\mathrm{Zn}^{2+} .$ What common term is used for ions such as $\mathrm{Zn}^{2+}$ when discussing enzyme activity?

Rabeya Zahid

Numerade Educator

00:40

Problem 77

An enzyme has the following pH dependence:
At what pH do you think this enzyme works best?

Rabeya Zahid

Numerade Educator

00:37

Problem 78

What enzyme is monitored in the diagnosis of infectious hepatitis?

Rabeya Zahid

Numerade Educator

00:49

Problem 79

The enzyme chymotrypsin catalyzes the following type of reaction:
On the basis of the classification given in Section $23-2,$ to which group of enzymes does chymotrypsin belong?

Rabeya Zahid

Numerade Educator

00:56

Problem 80

Nerve gases operate by forming covalent bonds at the active site of cholinesterase. Is this an example of competitive inhibition? Can the nerve gas molecules be removed by simply adding more substrate (acetylcholine) to the enzyme?

Rabeya Zahid

Numerade Educator

00:45

Problem 81

What would be the appropriate name for an enzyme that catalyzes each of the following reactions:

Rabeya Zahid

Numerade Educator

02:05

Problem 82

In Section $29-5,$ a reaction between pyruvate and glutamate to form alanine and $\alpha$ -ketoglutarate is given. How would you classify the enzyme that catalyzes this reaction?

Rabeya Zahid

Numerade Educator

00:39

Problem 83

A liver enzyme is made of four subunits: $2 \mathrm{A}$ and $2 \mathrm{B}$ The same enzyme, when isolated from the brain, has the following subunits: $3 \mathrm{A}$ and $1 \mathrm{B}$. What would you call these two enzymes?

Rabeya Zahid

Numerade Educator

00:31

Problem 84

What is the function of a ribozyme?

Rabeya Zahid

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01:09

Problem 85

Can an enzyme catalyze the forward reaction but not the backward reaction for its substrate-product pair(s)? Explain.

Rabeya Zahid

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00:43

Problem 86

Why was the discovery of ribozymes a remarkable event?

Rabeya Zahid

Numerade Educator

00:37

Problem 87

In some health food stores, it is possible to buy supplements that contain isolated enzymes. For example, the enzyme superoxide dismutase functions as an antioxidant in cells that are exposed to oxygen. Do you think that these supplements are likely to have significant value?

Rabeya Zahid

Numerade Educator

01:09

Problem 88

Caffeine is a stimulant that is taken by many people in the form of coffee, tea, chocolate, and cola beverages. It is also used by many athletes. Caffeine has many effects, including stimulating lipases. Given its effect on lipases and on glycogen phosphorylase, would you predict caffeine to be more effective as an aid to a runner in a $10 \mathrm{K}$ race or in a 1 -mile race?

Patina Herring

Numerade Educator

01:14

Problem 89

Caffeine is also a diuretic, which means it increases the movement of water through the kidneys and into the urine. Why would this potentially offset its value to a distance athlete?

Rabeya Zahid

Numerade Educator

00:38

Problem 90

Before the discovery of thermophilic bacteria that live in conditions of extreme heat and pressure, it was impossible to have an automated system of DNA synthesis. Explain why this was so, given that it takes temperatures of around $90^{\circ} \mathrm{C}$ to separate strands of DNA.

Rabeya Zahid

Numerade Educator

01:07

Problem 91

What characteristics of RNA make it likely to have catalytic ability? Why is DNA less likely to have catalytic activity?

Rabeya Zahid

Numerade Educator