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Introduction to General, Organic and Biochemistry

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

Chapter 22

Enzymes - all with Video Answers

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Chapter Questions

01:06

Problem 1

What is the difference between a catalyst and an enzyme?

Simon Sauvageau
Simon Sauvageau
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00:22

Problem 2

What are ribozymes made of?

Sabihah Khan
Sabihah Khan
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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
Simon Sauvageau
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00:48

Problem 4

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

Simon Sauvageau
Simon Sauvageau
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01:20

Problem 5

Why does the body need so many different enzymes?

Simon Sauvageau
Simon Sauvageau
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02:11

Problem 6

Trypsin catalyzes the hydrolysis of polypeptide chains at the carboxyl side of a lysine or arginine residue (Figure 22.1 ). 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
Sandra Lundell
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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
Sandra Lundell
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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
Sandra Lundell
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10:26

Problem 9

On the basis of the classification given in Section 22.2 decide to which group each of the following enzymes belongs:
(a) Phosphoglyceromutase
(b) Urease
(c) Succinate dehydrogenase
(d) Aspartase

Sandra Lundell
Sandra Lundell
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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
Simon Sauvageau
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01:58

Problem 11

What is the difference between reversible and irreversible noncompetitive inhibition?

Simon Sauvageau
Simon Sauvageau
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02:12

Problem 12

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 22.3 ). If the enzyme concentration on a molar basis is twice the maximum substrate concentration, would you obtain a saturation curve?

Sandra Lundell
Sandra Lundell
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01:14

Problem 13

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
Simon Sauvageau
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01:10

Problem 14

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
Simon Sauvageau
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03:22

Problem 15

A bacterial enzyme has the following temperature-dependent 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 $35^{\circ} \mathrm{C} ?$

Sandra Lundell
Sandra Lundell
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01:59

Problem 16

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
Sandra Lundell
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03:43

Problem 17

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: (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

Sandra Lundell
Sandra Lundell
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02:15

Problem 18

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
Sandra Lundell
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04:53

Problem 19

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

Ronald Prasad
Ronald Prasad
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02:38

Problem 20

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,
(b) a competitive inhibition, and
(c) a noncompetitive inhibition.

Sana Riaz
Sana Riaz
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01:15

Problem 21

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

Sandra Lundell
Sandra Lundell
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01:15

Problem 22

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

Sandra Lundell
Sandra Lundell
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00:56

Problem 23

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
Simon Sauvageau
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04:11

Problem 24

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

Sana Riaz
Sana Riaz
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00:51

Problem 25

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
Simon Sauvageau
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04:26

Problem 26

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 M urea is competitive or noncompetitive.

Sana Riaz
Sana Riaz
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02:59

Problem 27

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?

Sana Riaz
Sana Riaz
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02:36

Problem 28

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

Sana Riaz
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00:42

Problem 29

What is the difference between a $z$ ymogen and a proenzyme?

Simon Sauvageau
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01:31

Problem 30

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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05:40

Problem 31

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

Sana Riaz
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00:39

Problem 32

What is an isozyme?

Simon Sauvageau
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06:37

Problem 33

The enzyme glycogen phosphorylase initiates the phosphorolysis of glycogen to glucose- -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 $a$
(c) by changing the size and shape of the active site upon binding.

Sana Riaz
Sana Riaz
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01:10

Problem 34

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

Sana Riaz
Sana Riaz
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06:02

Problem 35

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

Sana Riaz
Sana Riaz
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04:36

Problem 36

Which type of regulation discussed in Section 22.6 is the least reversible? Explain.

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Sana Riaz
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01:18

Problem 37

The enzyme phosphofructokinase (PFK) (Chapter 27 ) has two types of subunits, $\mathrm{M}$ and $\mathrm{L}$, for muscle and liver, respectively. These subunits combine to form a tetramer. How many isozymes of PFK exist? What are their designations?

Rabeya Zahid
Rabeya Zahid
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05:12

Problem 38

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

Sana Riaz
Sana Riaz
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00:32

Problem 39

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
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00:33

Problem 40

Which disease(s) can be diagnosed by altered levels of amylase?

Simon Sauvageau
Simon Sauvageau
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03:26

Problem 41

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

Sana Riaz
Sana Riaz
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06:59

Problem 42

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

Sana Riaz
Sana Riaz
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04:58

Problem 43

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?

Sana Riaz
Sana Riaz
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01:33

Problem 44

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

Prashant Bana
Prashant Bana
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03:26

Problem 45

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
Noah Boudrie
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04:07

Problem 46

What is the biochemical reaction catalyzed by carbonic anhydrase?

Sana Riaz
Sana Riaz
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04:04

Problem 47

Why is $\mathrm{CO}_{2}$ transported as bicarbonate and carbonic acid in the blood?

Sana Riaz
Sana Riaz
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00:53

Problem 48

Why do we now believe that carbonic anhydrase is responsible for our perception of taste with carbonated beverages?

Simon Sauvageau
Simon Sauvageau
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01:03

Problem 49

(Chemical Connections 22 B) PKM $\zeta$ is a type of enzyme called a kinase. Kinases are very important in metabolism. Look through the metabolism chapters (Chapters 26 and 27 ) and find two examples of kinases. What reactions do kinases catalyze?

Simon Sauvageau
Simon Sauvageau
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04:51

Problem 50

(Chemical Connections $22 \mathrm{B}$ ) Explain how researchers used the drug ZIP to test its effect on long-term memory. How did they know that food aversion was a longterm memory phenomenon?

Sana Riaz
Sana Riaz
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06:20

Problem 51

(Chemical Connections 22 B ) Why would researchers want to be able to selectively block long-term memory?

Sana Riaz
Sana Riaz
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04:57

Problem 51

(Chemical Connections $22 \mathrm{C}$ ) What is the strategy in drug design to fight AIDS?

Sana Riaz
Sana Riaz
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04:25

Problem 52

(Chemical Connections $22 \mathrm{C}$ ) What is the strategy in drug design to fight AIDS?

Sana Riaz
Sana Riaz
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05:03

Problem 53

(Chemical Connections $22 \mathrm{C}$ ) Why did scientists want to create a drug to inhibit cGMP diesterases?

Sana Riaz
Sana Riaz
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05:13

Problem 54

(Chemical Connections $22 \mathrm{C}$ ) How can the crystal structures of enzymes be used in drug design?

Sana Riaz
Sana Riaz
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05:34

Problem 55

(Chemical Connections $22 \mathrm{C}$ ) Would reducing the population of intestinal bacteria be a useful way to alleviate the side effects of treatment for colon cancer?

Sana Riaz
Sana Riaz
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04:57

Problem 56

(Chemical Connections 22 D) How does feedback inhibition play a role in the activity of phosphofructokinase?

Sana Riaz
Sana Riaz
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04:40

Problem 57

(Chemical Connections 22 D) What is the relationship between protein modification and allosteric control of phosphofructokinase?

Sana Riaz
Sana Riaz
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04:41

Problem 58

(Chemical Connections $22 \mathrm{C}$ ) What role does $\mathrm{Mn}^{2+}$ play in anchoring the substrate in the active site of protein kinase?

Sana Riaz
Sana Riaz
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05:59

Problem 59

(Chemical Connections $22 \mathrm{C}$ ) 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?

Sana Riaz
Sana Riaz
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04:10

Problem 60

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

Sana Riaz
Sana Riaz
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02:10

Problem 61

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
Prashant Bana
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03:40

Problem 62

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?

Sana Riaz
Sana Riaz
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02:49

Problem 63

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

Sana Riaz
Sana Riaz
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06:00

Problem 64

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

Sana Riaz
Sana Riaz
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04:09

Problem 65

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

Sana Riaz
Sana Riaz
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03:37

Problem 66

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?

Sana Riaz
Sana Riaz
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05:02

Problem 67

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

Sana Riaz
Sana Riaz
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05:25

Problem 68

What enzyme is monitored in the diagnosis of infectious hepatitis?

Sana Riaz
Sana Riaz
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01:11

Problem 69

The enzyme chymotrypsin catalyzes the following type of reaction: On the basis of the classification given in Section 22.2 to which group of enzymes does chymotrypsin belong?

Sana Riaz
Sana Riaz
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05:17

Problem 70

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?

Sana Riaz
Sana Riaz
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02:44

Problem 71

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

Sana Riaz
Sana Riaz
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05:01

Problem 72

In Section $28.5,$ a reaction between pyruvate and glutamate to form alanine and $\alpha$ -ketoglutarate is given. How would you classify the enzyme that catalyzes this reaction?

Sana Riaz
Sana Riaz
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05:29

Problem 73

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?

Sana Riaz
Sana Riaz
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04:11

Problem 74

What is the function of a ribozyme?

Sana Riaz
Sana Riaz
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04:16

Problem 75

Can an enzyme catalyze the forward reaction but not the backward reaction for its substrate-product $\operatorname{pair}(\mathrm{s}) ?$ Explain

Sana Riaz
Sana Riaz
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06:20

Problem 76

Why was the discovery of ribozymes a remarkable event?

Sana Riaz
Sana Riaz
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05:11

Problem 77

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?

Sana Riaz
Sana Riaz
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09:49

Problem 78

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?

Sana Riaz
Sana Riaz
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05:22

Problem 79

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?

Sana Riaz
Sana Riaz
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03:49

Problem 80

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 replication. Explain why this was so, given that it takes temperatures of around $90^{\circ} \mathrm{C}$ to separate strands of DNA.

Sana Riaz
Sana Riaz
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03:44

Problem 81

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

Sana Riaz
Sana Riaz
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