Ch. 3

Question 1

What is the measure of disorder in a system called?

Answer 1

Entropy

Question 2

Which of the following represents energy in its most disordered form?

Answer 2

Heat energy

Question 3

Because they generate order (by surviving, growing and forming complex communities), living cells defy the second law of thermodynamics.

Answer 3

False

Question 4

Which of the following does NOT follow the first law of thermodynamics?

Answer 4

The use of heat to burn foodstuff inside cells

Question 5

What is the origin of the energy that animals acquire by eating plants or other animals?

Answer 5

Sunlight

Question 6

Which energy conversion characterizes photosynthesis?

Answer 6

Electromagnetic (light) energy → chemical bond energy

Question 7

In both plants and animals, the process of “controlled burning” that extracts energy from food molecules is a process of gradual:

Answer 7

oxidation.

Question 8

Which of the following does not describe oxidation?

Answer 8

The conversion of a chlorine atom to Cl-

Question 9

Which of the following does describe oxidation?

Answer 9

The addition of oxygen atoms to a molecule and The removal of electrons from a molecule

Question 10

Which of the following statements is NOT true?

Answer 10

Hydrogenation reactions are oxidations, and dehydrogenation reactions are reductions.

Question 11

Which of the following statements IS true?

Answer 11

• Oxidation and reduction reactions always occur simultaneously.
• When a sugar molecule is oxidized to CO2 and H2O, O2 molecules are reduced.

Question 12

Chemical reactions proceed spontaneously only in the direction that:

Answer 12

leads to a loss of free energy.

Question 13

In thermodynamics, what does the term “free energy” refer to?

Answer 13

Energy that can be harnessed to do work or drive chemical reactions

Question 14

Which statement about enzymes is NOT true?

Answer 14

Enzymes can force reactions to occur that are overall energetically unfavorable.

Question 15

Which statement about enzymes IS true?

Answer 15

• Enzymes can speed up energetically favorable reactions.

- Enzymes can help build highly ordered structures.

Question 16

What is the term for the extra energy boost required to initiate an energetically favorable reaction?

Answer 16

Activation energy

Question 17

An enzyme can lower the activation energy of a reaction.

Answer 17

TRUE

Question 18

.After an enzyme catalyzes a reaction, the enzyme has been consumed and cannot perform additional reactions.

Answer 18

FALSE

Question 19

A reaction occurs spontaneously only if the change in free energy (/δ∊λταG) is:

Answer 19

negative.

Question 20

Energetically favorable reactions are those that create disorder by decreasing the free energy of the system to which they belong.

Answer 20

True

Question 21

Which of the following results in increased disorder?

Answer 21

Dissolving salt in water

Question 22

nergetically unfavorable reactions can occur if they are coupled to a second reaction with a negative /δ∊λτα Gso large that the net /δ∊λτα Gof the entire process is negative.

Answer 22

True

Question 23

Which is NOT true of a reaction at chemical equilibrium?

Answer 23

Both the forward and reverse reactions have completely stopped.

Question 24

Which IS true of a reaction at chemical equilibrium?

Answer 24

• /delta G is equal to zero.

- The rates of the forward and reverse reactions are equal.

Question 25

The free energy change (/δ∊λτα G) and the standard-free energy change(/δ∊λτα G°) of a reaction differ in that /δ∊λταG depends on the concentrations of the molecules in the reaction, whereas for /δ∊λτα G°, the concentrations are set to a fixed value.

Answer 25

true

Question 26

For the simple reaction Y → X, the equilibrium constant K is:

Answer 26

[X]/[Y]

Question 27

For every 1.42 kcal/mole difference in free energy at 37°C, K changes by a factor of:

Answer 27

10

Question 28

Consider the reaction A + B → AB. How is the equilibrium constant expressed for this reaction with two substrates and a single product?

Answer 28

K = [AB]/[A][B]

Question 29

Two molecules will bind to each other by means of noncovalent bonds if the /δ∊λτα Γ° of the interaction is:

Answer 29

negative (the free energy of the product is lower than the sum of the free energies of the unbound partners).

Question 30

Consider two molecules that associate with each other through hydrogen bonds. The larger the equilibrium constant, K, for this association:

Answer 30

the more tightly the two molecules will bind.

Question 31

The overall free-energy change for coupled reactions is equal to the sum of the free-energy changes for each individual reaction.

Answer 31

true

Question 32

In cells, small molecules can diffuse over short distances quickly.

Answer 32

TRUE

Question 33

The rate at which an enzyme will encounter its substrate depends on:

Answer 33

the concentration of the substrate.

Question 34

In an enzyme catalyzed reaction, a low value of KM indicates that a substrate binds:

Answer 34

very tightly to the enzyme.

Question 35

When an enzyme lowers the activation energy for the forward reaction X → Y, it also lowers the reaction rate for the reverse reaction Y → X by the same amount.

Answer 35

True

Question 36

In isolation, the formation of an activated carrier molecule, such as ATP, NADH, or NADPH, is an energetically unfavorable reaction.

Answer 36

TRUE

Question 37

The/δ∊λτα Γ° of the hydrolysis reaction of ATP is -7.3 kcal/mole, but in a cell the actual /δ∊λτα Γ is much more negative because:

Answer 37

ATP is much higher in concentration than the products ADP and Pi.

Question 38

Which statement is true about the removal of a terminal phosphate from ATP?

Answer 38

The reaction is energetically favorable.

Question 39

Which statement is NOT true about the removal of a terminal phosphate from ATP?

Answer 39

• The reaction is a condensation reaction.

- The reaction is associated with a positive change in /δ∊λτα Γ°.

Question 40

The formation of ATP can be coupled to energetically unfavorable reactions to allow them to proceed.

Answer 40

False

Question 41

What is the difference between NAD+ and NADH?

Answer 41

NADH carries an extra proton and two high-energy electrons.

Question 42

Which of the following statements is NOT true?

Answer 42

NADPH is an activated carrier molecule that is used primarily by plants.

Question 43

Which of the following statements IS true?

Answer 43

• NADPH is an activated carrier molecule that is usually used in biosynthetic reactions to build energy-rich molecules.
• NADH is an activated carrier molecule that is usually used in oxidation reactions to produce ATP.

Question 44

Which of the following is true?

Answer 44

NADPH and NADH are used in independent pathways in cells.

Question 45

Which of the following is NOT true?

Answer 45

• NADPH loses a phosphate group to form NADH during biosynthetic reactions.
• NADPH and NADH deliver electrons to the same set of enzymes.
• NADH caries electrons in animal calls and NADPH does the same in plants.

Question 46

Activated carriers that transfer methyl, carboxyl, and glucose groups for the purpose of biosynthesis are typically generated in reactions coupled to ATP hydrolysis.

Answer 46

True

Question 47

Which statement is true about the breakdown of polymers?

Answer 47

The reaction is associated with a negative change in free energy.

Question 48

Which statement is NOT true about the breakdown of polymers?

Answer 48

• The reaction occurs without the need of enzymes.

- The reaction is energetically unfavorable.

Question 49

What is the difference between catabolism and anabolism? Give an example of each.

Answer 49

Catabolic pathways break down foodstuffs into smaller molecules to generate energy for the cell; anabolic pathways use energy to drive the synthesis of the molecules that form the cell. Cellular respiration is an example of catabolism, and photosynthesis is an example of anabolism.

Question 50

Does an enzyme change the Δ G° of the reaction it catalyzes?

Answer 50

An enzyme functions by lowering the activation energy of a reaction. At the same time, it lowers the activation energy of the reverse reaction by the same amount. Therefore, the forward and reverse reactions will be accelerated by the same factor. So, the equilibrium point for the reaction, and therefore its Δ G°, will not change.

Question 51

The organic chemistry of living cells is said to be special for two reasons: it occurs in an aqueous environment and it accomplishes some very complex reactions. But do you suppose it is really all that much different from the organic chemistry carried out in the top laboratories in the world? Why or why not?

Answer 51

Organic chemistry in laboratories—even the very best—is rarely carried out in a water environment because of low solubility of some components and because water is reactive and usually competes with the intended reaction. The most dramatic difference, however, is the complexity. It is critical in laboratory organic chemistry to use pure components to ensure a high yield of the intended product. By contrast, living cells carry out thousands of different reactions simultaneously with good yield and virtually no interference between reactions. The key, of course, is that cells use enzyme catalysts, which bind substrate molecules in an active site, where they are isolated from the rest of the environment. There the reactivity of individual atoms is manipulated to encourage the correct reaction. It is the ability of enzymes to provide such special environments—miniature reaction chambers—that allows the cell to carry out an enormous number of reactions simultaneously without cross talk between them.