The Importance of Energy Changes and Electron Transfer in Metabolism

Question 1

Which of the following statements concerning the free energy change (ΔG) is false?

a. The energy change for a reaction depends only on the initial and final states, and is independent of the path
taken.

b. The overall energy change for a reaction could be calculated by summing the energy changes for a series of separate reactions that could convert the reactants to the products.

c. The rate of a reaction can be determined from the energy change.

d. The energy change is a function of the concentrations of the products and reactants at start.

e. All of the answers are true

Answer 1

c

Question 2

The standard state of a solution is taken as
a. 1 atmosphere of pressure.
b. the pure solute.
c. 1 molar concentration.
d. 1 % by weight
e. none of the above.

Answer 2

c

Question 3

Consider this rxn which has a
ΔG° = +0.4 kJ/mol.

A + B ↔ C + D

1 M A, 1 M B, 0.1 M C and 0.1 M D are added to a container at room temperature. Which of the following statements is true?

a. The reaction will proceed in the forward direction to reach equilibrium.
b. The reaction will proceed in the backward direction to reach equilibrium.
c. The reaction will not proceed in either direction; it is already at equilibrium.
d. Cannot be determined from the information provided.

Answer 3

a

Question 4

Consider this rxn which has a
ΔG° = +0.4 kJ/mol.

succinate + FAD ↔ fumarate + FADH2

1 mM of each compound are mixed & the reaction is allowed to come to equilibrium.

Which statement is correct about
the resulting concentration of FAD at equilibrium?

a. [FAD] > [FADH2]
b. [FAD] < [FADH2]
c. [FAD] = [FADH2]
d. Cannot be determined from the information provided.

Answer 4

a

Question 5

Consider this rxn which has a
ΔG° = +0.4 kJ/mol.

A + B ↔ C + D

1 M A, 1 M B, 0.1 M C and 0.1 M D are added to a container at room temperature. Which of the following statements is true?

a. ΔG < 0 (i.e., it’s negative)
b. ΔG = 0
c. ΔG > 0 (i.e., it’s positive)
d. Cannot be determined from the information provided.

Answer 5

a

Question 6

Which of the following is not true concerning standard states?
a. For pure liquids, the standard state is 1M
b. For pure solids, the standard state is the pure solid itself
c. For gases, the standard state is 1 atmosphere
d. For solutes, the standard state is 1M
e. All of the answers are true

Answer 6

a

Question 7

A biological reaction with a significantly postive ΔG under cellular conditions may proceed in the forward direction because

a. The cell will change the concentrations of the substrates and products so that the reaction can occur
b. The cell will raise the temperature, thereby affecting the overall thermodynamics of the reaction

c. the reaction can be coupled to a reaction with a more significant negative ΔG

d. reactions with positive ΔG values always proceed in the forward direction

e. None of these

Answer 7

c

Question 8

I am performing a reaction, A → B, with ΔG°’ = −0.3 kJ/mol.

I start the reaction with 10 mM A and no B.

Afterallowing the reaction to proceed for 24 hrs at room temperature and atmospheric pressure, I analyze a sample of the
reaction mix to find I now have 1 mM A and 9 mM B. Which of the following conclusions should I make?

a. The reaction has reached equilibrium.
b. I should come back again later; equilibrium has not yet been reached.
c. The formation of B from A is thermodynamically unfavorable, so I should find another starting material to
make B.
d. I must’ve screwed up; there’s no way I could get that result with that ΔG°’

Answer 8

d

Question 9

I am performing a reaction, A → B, with ΔG°’ = −5000 kJ/mol. I start the reaction with 10 mM A and no B. After allowing the reaction to proceed for 24 hrs at room temperature and atmospheric pressure, I analyze a sample of the
reaction mix to find I now have 8 mM A and 2 mM B. Which of the following conclusions should I make?

a. The reaction has reached equilibrium.
b. I should come back again later; equilibrium has not yet been reached.
c. The formation of B from A is thermodynamically unfavorable, so I should find another starting material to
make B.
d. I must’ve screwed up; there’s no way I could get that result with that ΔG°’

Answer 9

b

Question 10

Biochemists use a modified value for standard ΔG values because
a. all reagents are not at a 1 molar concentration.
b. the pH in living systems is seldom, if ever, near 0.
c. the concentration of water is not at 1 molar concentration.
d. the reagents are not one molar and the pH = 7.
e. All of these justify why biochemists use a special ΔG value.

Answer 10

b

Question 11

Which best describes the ΔG for hydrolysis of creatine phosphate under cellular conditions in which the concentration
of creatine phosphate, creatine, and phosphate all equal 1 mM at 25°C. The ΔG° for the hydrolysis of creatine phosphate
at 25°C is −43 kJ/mol.
a. ΔG < −43 kJ/mol
b. ΔG = −43 kJ/mol
c. −43 kJ/mol < ΔG ≤ 0 kJ/mol
d. ΔG > 0 kJ/mol

Answer 11

a

Question 12

By definition, a spontaneous reaction is one in which
a. energy is released.
b. energy is absorbed.
c. the energy change is zero.
d. the reaction happens quickly
e. energy is released and the reaction happens quickly

Answer 12

a

Question 13

The standard state usually used in biochemistry (ΔG°’) includes
a. all concentrations at 1 M.
b. all concentrations at 1 M, except for [H+], which is 10−
7 M.
c. same as a), but at 25° C.
d. same as b), but at 25° C.
e. None of the answers

Answer 13

b

Question 14

“Metabolism” refers to
a. the breakdown of larger molecules into smaller ones.
b. the production of larger molecules from smaller ones.
c. both of these
d. none of these

Answer 14

c

Question 15

The production of larger molecules from smaller ones is called
a. metabolism.
b. catabolism.
c. anabolism.
d. none of these

Answer 15

c

Question 16

In general, catabolism
a. releases energy.
b. absorbs energy.
c. neither absorbs nor releases energy.

Answer 16

a

Question 17

In general, catabolism
a. is an oxidative process that releases energy
b. is a reductive process that releases energy
c. is an oxidative process that requires energy
d. is a reductive process that requires energy
e. none of these

Answer 17

a

Question 18

Which of the following statements apply to anabolism?
a. proceeds in stages
b. requires energy
c. requires reducing agents
d. all of these

Answer 18

d

Question 19

Living things are _____
a. a closed system
b. an open system
c. an isolated system
d. none of these

Answer 19

b

Question 20

An isolated system can exchange ______ with its surroundings
a. energy but not matter
b. matter but not energy
c. both matter and energy
d. neither matter nor energy

Answer 20

d

Question 21

“Oxidation” refers to
a. the loss of oxygen.
b. the gain of oxygen.
c. the loss of electrons.
d. the gain of electrons.

Answer 21

c

Question 22

An organism that is at equilibrium would be
a. in a steady state
b. an open system
c. dead
d. energetically balanced

Answer 22

c

Question 23

An oxidizing agent
a. loses oxygen.
b. gains oxygen.
c. loses electrons.
d. gains electrons.

Answer 23

d

Question 24

Consider the reaction of alcohol dehydrogenase.

CH₃-CH₂OH + NAD⁺ → CH₃-CHO + NADH + H⁺

Which is the oxidizing agent?

a. Ethanol
b. NAD⁺
c. Acetaldehyde
d. NADH
e. H⁺

Answer 24

b

Question 25

Consider the reaction of alcohol dehydrogenase.

CH₃-CH₂OH + NAD⁺ → CH₃-CHO + NADH + H⁺

Which molecule is reduced?

a. Ethanol
b. NAD⁺
c. Acetaldehyde
d. NADH
e. H⁺

Answer 25

b

Question 26

Consider the reaction of alcohol dehydrogenase.

CH₃-CH₂OH + NAD⁺ → CH₃-CHO + NADH + H⁺

Which molecule loses electrons?

a. Ethanol
b. NAD⁺
c. Acetaldehyde
d. NADH
e. H⁺

Answer 26

a

Question 27

During reduction
a. electrons are lost.
b. electrons are gained.
c. electrons may either be lost or gained.
d. hydrogen is formed.

Answer 27

a

Question 28

In general, the anabolic pathways tend to involve oxidation reactions.
a. True
b. False

Answer 28

b

Question 29

Which of the following is not true?
a. Molecular oxygen is always a substrate in oxidation reactions.
b. Oxidation reactions involve the movement of electrons from one molecule to another
c. When a molecule is oxidized, it loses electrons
d. Reduction involves the gain of electrons

Answer 29

a

Question 30

Which of the following coenzymes is not a carrier of electrons in biological redox reactions?
a. Coenzyme A
b. Niacin.
c. Riboflavin.
d. Transition metal ions, such as those of iron or copper.
e. All of these can be intermediate electron carriers.

Answer 30

a

Question 31

In biological redox reactions, hydrogen ions are usually transferred along with electrons.
a. True
b. False

Answer 31

a

Question 32

Which of the following coenzymes is derived from riboflavin?
a. Coenzyme A
b. NAD+
c. FAD
d. All of the above.
e. None of the above.

Answer 32

c

Question 33

Which of the following is not a part of FAD?
a. Ribitol
b. isoalloxazine
c. adenine
d. ribose
e. nicotinamide

Answer 33

e

Question 34

The conversion of NAD+
to NADH is an example of reduction because
a. the pyridine ring loses electrons (and a hydrogen)
b. the pyridine ring gains electrons (and a hydrogen)
c. the adenine ring loses electrons
d. the adenine ring gains electrons

Answer 34

b

Question 35

In the coenzyme FAD the site to which electrons are transferred is
a. the ribose moiety of the molecule
b. a purine ring system
c. a pyrimidine ring system
d. a nitrogen-containing ring system

Answer 35

d

Question 36

What happens to the entropy when ATP is hydrolysed to ADP?
a. Entropy increases
b. Entropy decreases.
c. Entropy doesn’t change.
d. ATP has no entropy.

Answer 36

a

Question 37

The oxidation of nutrients supplies the energy to produce ATP.
a. True
b. False

Answer 37

a

Question 38

In order to drive the synthesis of ATP, the hydrolysis of an organic phosphate
a. must have a higher free energy change.
b. must have a lower free energy change.
c. must have a free energy change equal to that of ATP.

Answer 38

a

Question 39

Consider these reactions:

ATP → ADP + Pi
ΔG°’ = −31 kJ/mol

glucose-6-phosphate → glucose + Pi
ΔG°’ = −13 kJ/mol

glucose + ATP → glucose-6-phosphate + ADP
ΔG°’ = ?

What is the ΔG°’ of the last reaction?
a. −44 kJ/mol
b. −18 kJ/mol
c. +18 kJ/mol
d. +44 kJ/mol
e. Cannot be determined from the information provided.

Answer 39

b

Question 40

ATP is a good source of energy to run metabolic reactions for all the following reasons, except:
a. The pyrophosphate bond has a high energy of hydrolysis.
b. The sugar group is very reactive.
c. The bonds between the phosphates are acid anhydrides.
d. The phosphate groups can combine readily with other molecules.
e. All of these explain why ATP is a good energy source.

Answer 40

b

Question 41

The body allows energy consuming reactions to occur by coupling them with reactions which have a negative ΔG.
a. True
b. False

Answer 41

a

Question 42

The number of degrees of freedom a molecule has is related to the numbers of resonant structures it has.
a. True
b. False

Answer 42

a

Question 43

What happens to the entropy of a molecule as the number of resonance structures increases?

a. Entropy also increases.
b. Entropy decreases.
c. Entropy has no relationship to the number of resonance structures.

Answer 43

a

Question 44

Many cells oxidize fatty acids to produce ATP. If no ATP were produced, the ΔG°’ of this process would be
a. unchanged
b. a larger positive number
c. a larger negative number
d. impossible to determine

Answer 44

c

Question 45

When we say that the efficiency of glycolysis is about 33% we mean that
a. 2 ATP are produced and 6 ATP are involved in the overall process
b. 2 ATP are produced in the oxidation of glucose, which contains six carbon atoms
c. the energy used to phosphorylate 2 ATP is 33% of the energy released in the process
d. all of these

Answer 45

c

Question 46

The energy released during metabolism of nutrients can be used to synthesize ATP from ADP and phosphate.
a. True
b. False

Answer 46

a

Question 47

In order to initiate many metabolic pathways it is necessary to activate the starting materials.
a. True
b. False

Answer 47

a

Question 48

If the reaction A → B has ΔG = +25 Joule/mol and the reaction B → C has ΔG = −15 Joule/mol, the overall energy
change A → C will be
a. −40 Joule/mol.
b. −15 Joule/mol.
c. +10 Joule/mol.
d. +40 Joule/mol.
e. You cannot determine the overall reaction from the given data.

Answer 48

c

Question 49

Which of the following are examples of endergonic processes?
a. protein synthesis and active transport
b. protein synthesis and oxidation of carbohydrates
c. active transport and oxidation of carbohydrates
d. oxidation of fats and of carbohydrates

Answer 49

a

Question 50

Which of the following are examples of exergonic processes?
a. protein synthesis and active transport
b. protein synthesis and oxidation of carbohydrates
c. active transport and oxidation of carbohydrates
d. oxidation of fats and of carbohydrates

Answer 50

d

Question 51

The phosphorylation of ADP to produce ATP is endergonic because
a. a negatively charged ion is bonded to a molecule that already carries a negative charge
b. ATP is more stable than ADP
c. the entropy of the products is less than that of the reactants
d. polyphosphate chains are the storage form of phosphorus in living organisms

Answer 51

a

Question 52

Spontaneous reaction always occurs at a relatively fast rate.
a. True
b. False

Answer 52

b

Question 53

The efficiency of aerobic metabolism is greater than that of anaerobic metabolism even though much more energy is
released in aerobic than in anaerobic metabolism because
a. aerobic metabolism is linked to oxygen, which is a more powerful oxidizing agent than those in anaerobic
metabolism
b. aerobic metabolism produces carbon dioxide and water
c. aerobic metabolism traps much more energy in the form of ATP than does anaerobic metabolism
d. anaerobic metabolism produces two- and three-carbon compounds

Answer 53

c

Question 54

The hydrolysis of ATP can be used to drive reactions that have a ΔG°’ that is
a. greater than +5 kJ/mol
b. less than +5 kJ/mol
c. between +20 and +40 kJ/mol
d. not possible to determine from the information in this chapter

Answer 54

b

Question 55

The linking of an exergonic reaction to drive an endergonic reaction is called:
a. coupling
b. a state function
c. resonance
d. catabolsim

Answer 55

a

Question 56

What happens to the entropy when ATP is hydrolysed to ADP?
a. Entropy increases
b. Entropy decreases.
c. Entropy doesn’t change.
d. ATP has no entropy.

Answer 56

a

Question 57

In metabolism the term “activation” refers to
a. conversion of a component of a metabolic pathway into a reactive compound.
b. addition of a catalyst.
c. bypassing endergonic reactions in a pathway.
d. bypassing the unreactive components of a pathway.

Answer 57

a

Question 58

An example of an activation step in metabolism is
a. the hydrolysis of a triacylglycerol.
b. the cis-trans isomerization of retinal.
c. the formation of an acyl derivative of coenzyme A.
d. the formation of the peptide bond.

Answer 58

c

Question 59

Which of the following is not a mechanism used to activate substrates for further metabolism?
a. Addition of a phosphate group.
b. Combination with a vitamin, such as coenzyme A.
c. Hydrolyzing a polymer into its component monomers.
d. Addition of a phosphate group or combining with a vitamin.
e. All of these processes activate substrates.

Answer 59

c

Question 60

Metabolism takes place in stages
a. because enzymes cannot catalyze the process efficiently
b. and allows for efficient production and use of energy
c. because large free energy changes cannot occur in living organisms
d. to use highly unreactive compounds

Answer 60

b

Question 61

For a general equation , the relation between the free-energy change () for the reaction under any condition and the
free energy change under standard conditions () can be written as _____.

a.
ΔG = ΔG° + RT ln
{[𝐴]^𝑎[𝐵]^𝑏} / {[𝐶]^𝑐[𝐷]^𝑑}

b.
ΔG = ΔG° + RT ln
{[𝐶]^𝑐[𝐷]^𝑑} / {[𝐴]^𝑎[𝐵]^𝑏}

c.
ΔG = ΔG° + R ln
{[𝐴]^𝑎[𝐵]^𝑏} / {[𝐶]^𝑐[𝐷]^𝑑}

d.
ΔG = ΔG° + R ln
{[𝐶]^𝑐[𝐷]^𝑑} / {[𝐴]^𝑎[𝐵]^𝑏}

Answer 61

b

Question 62

Identify the value of if a reaction is at equilibrium and the equilibrium constant () for the reaction is 20. (The values of R and T are 8.31 J mol-1 K-1and 273.0 K, respectively)

a. -2941.008 J mol-1
b. -6097.091 J mol-1
c. -2951.555 J mol-1
d. -6796.208 J mol-1

Answer 62

d

Question 63

Explain what happens to carbon atoms in biological oxidation-reduction reactions.

Answer 63

In many biological oxidation-reduction reactions, the oxidation state of carbon atoms changes. For
example, an alkane (carbon in its most reduced form) is oxidized to an alcohol, an aldehyde, a
carboxylic acid, and ultimately carbon dioxide. Each of these oxidations requires the loss of two
electrons.

Question 64

Among the following organophosphates, which compound has the highest amount of free energy of hydrolysis?
a. Phosphoenolpyruvate
b. Glucose 6-phosphate
c. Adenosine triphosphate
d. Acetyl phosphate

Answer 64

a

Question 65

Explain the differences between catabolism and anabolism.

Answer 65

Catabolism refers to the breakdown of nutrients to provide energy. Anabolism refers to the
synthesis of biomolecules from simpler compounds. Catabolism releases energy, whereas
anabolism consumes energy. The ATP produced by catabolism is hydrolyzed to release the energy
required by anabolism