Deck 15: The Importance of Energy Changes and Electron Transfer in Metabolism

Question 1

Living things are _____

A) a closed system
B) an open system
C) an isolated system
D) none of these

Answer 1

an open system

Question 2

I am performing a reaction, A → B, with Δ G ° ' = − 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 Δ G ° '

Answer 2

I should come back again later; equilibrium has not yet been reached.

Question 3

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 3

energy is released.

Question 4

A biological reaction with a significantly postive Δ G 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 Δ G
D) reactions with positive Δ G values always proceed in the forward direction
E) None of these

Question 5

In general, catabolism

A) releases energy.
B) absorbs energy.
C) neither absorbs nor releases energy.

Question 6

The production of larger molecules from smaller ones is called

A) metabolism.
B) catabolism.
C) anabolism.
D) none of these

Question 7

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.

Question 8

Which of the following statements concerning the free energy change ( Δ G) 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

Question 9

"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

Question 10

I am performing a reaction, A → B, with Δ G ° ' = − 0.3 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 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 Δ G ° '

Question 11

Biochemists use a modified value for standard Δ G 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 Δ G value.

Question 12

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

Question 13

Which best describes the Δ G 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 Δ G ° for the hydrolysis of creatine phosphate at 25 ° C is − 43 kJ\mol.

A) Δ G − 43 kJ\mol
B) Δ G = − 43 kJ\mol
C) − 43 kJ\mol Δ G ≤ 0 kJ\mol
D) Δ G > 0 kJ\mol

Question 14

Consider this rxn which has a Δ G ° = +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) Δ G
B) Δ G = 0
C) Δ G > 0 (i.e., it's positive)
D) Cannot be determined from the information provided.

Question 15

Consider this rxn which has a Δ G ° = +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.

Question 16

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

Question 17

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

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

Question 19

Consider this rxn which has a Δ G ° = +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]
C) [FAD] = [FADH₂]
D) Cannot be determined from the information provided.

Question 20

The standard state usually used in biochemistry ( Δ G ° ') 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

Question 21

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.

Question 22

Consider these reactions: What is the Δ G ° ' 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.

Question 23

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.

Question 24

Exhibit 15A Consider the reaction of alcohol dehydrogenase. Refer to Exhibit 15A. Which molecule loses electrons?

A) Ethanol
B) NAD⁺
C) Acetaldehyde
D) NADH
E) H⁺

Question 25

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.

Question 26

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

Question 27

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.

Question 28

An oxidizing agent

A) loses oxygen.
B) gains oxygen.
C) loses electrons.
D) gains electrons.

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

Question 30

Exhibit 15A Consider the reaction of alcohol dehydrogenase. Refer to Exhibit 15A. Which molecule is reduced?

A) Ethanol
B) NAD⁺
C) Acetaldehyde
D) NADH
E) H⁺

Question 31

The oxidation of nutrients supplies the energy to produce ATP.

Question 32

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

Question 33

Exhibit 15A Consider the reaction of alcohol dehydrogenase. Refer to Exhibit 15A. Which is the oxidizing agent?

A) Ethanol
B) NAD⁺
C) Acetaldehyde
D) NADH
E) H⁺

Question 34

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.

Question 35

Which of the following is not a part of FAD?

A) Ribitol
B) isoalloxazine
C) adenine
D) ribose
E) nicotinamide

Question 36

In biological redox reactions, hydrogen ions are usually transferred along with electrons.

Question 37

In general, the anabolic pathways tend to involve oxidation reactions.

Question 38

An organism that is at equilibrium would be

A) in a steady state
B) an open system
C) dead
D) energetically balanced

Question 39

"Oxidation" refers to

A) the loss of oxygen.
B) the gain of oxygen.
C) the loss of electrons.
D) the gain of electrons.

Question 40

During reduction

A) electrons are lost.
B) electrons are gained.
C) electrons may either be lost or gained.
D) hydrogen is formed.

Question 41

Many cells oxidize fatty acids to produce ATP. If no ATP were produced, the Δ G ° ' of this process would be

A) unchanged
B) a larger positive number
C) a larger negative number
D) impossible to determine

Question 42

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

Question 43

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.

Question 44

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

Question 45

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.

Question 46

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.

Question 47

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.

Question 48

The body allows energy consuming reactions to occur by coupling them with reactions which have a negative Δ G.

Question 49

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

Question 50

If the reaction A → B has Δ G = +25 Joule\mol and the reaction B → C has Δ G = − 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.

Question 51

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.

Question 52

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

Question 53

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

Question 54

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

Question 55

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

Question 56

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

Question 57

Spontaneous reaction always occurs at a relatively fast rate.

Question 58

The linking of an exergonic reaction to drive an endergonic reaction is called:

A) coupling
B) a state function
C) resonance
D) catabolsim

Question 59

In order to initiate many metabolic pathways it is necessary to activate the starting materials.

Question 60

The hydrolysis of ATP can be used to drive reactions that have a Δ G ° ' 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

Question 61

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

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^-1 and 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

Question 63

​ 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

Question 64

​ 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)
B)
C)
D)

Question 65

Explain the differences between catabolism and anabolism.