Deck 10: Introduction to Metabolism

Question 1

The flow of material through a reaction pathway usually depends on .

A) control at several steps in the pathway
B) control of the first step of the pathway
C) covalent modification of the enzyme that catalyzes the reaction
D) feed-forward activation

Answer 1

control at several steps in the pathway

Question 2

Phosphorylation at the expense of ATP is catalyzed by .

A) protein kinases
B) phosphoryl isomerases
C) phosphatases
D) All of the above

Answer 2

protein kinases

Question 3

Which is not generally a molecule used to conserve energy?

A) ATP
B) NADH
C) FAD
D) QH₂

Answer 3

FAD

Question 4

The reactions that digest foods in the mouth, stomach and intestine are classified as reactions.

A) proteolytic cleavage
B) hydrolysis
C) free radical
D) reduction

Question 5

The flow of material through a metabolic pathway is called the .

A) current
B) degree of amplification
C) cascade effect
D) flux

Question 6

Which statement is false about most metabolic pathways?

A) Most pathways are reversible under physiological conditions.
B) Pathways serve to increase the efficiency of energy transfers.
C) The rates of pathway reactions vary to respond to changing conditions.
D) The enzymes that catalyze reactions in metabolic pathways generally catalyze only a single step.

Question 7

Intermediary metabolism is the term applied to reactions that .

A) degrade molecules
B) synthesize large molecules such as proteins
C) convert glucose to pyruvate
D) involve low molecular weight metabolites

Question 8

For a step in a reaction pathway to serve as a control point it should be .

A) irreversible
B) endergonic
C) far from equilibrium
D) Both A and C
E) All of the above

Question 9

The percent of genomes involved in intermediary and energy metabolisms in a wide variety of species is about

A) 10%.
B) 15-30%.
C) 20-50%.
D) 30% or more.

Question 10

Consider the synthesis of a biopolymer in which the addition of successive monomers occurs by the same kind of reactions). The synthesis of the polymer is a pathway.

A) linear
B) cyclic
C) spiral
D) branched

Question 11

Which is usually the slowest way to regulate a reaction in a metabolic pathway?

A) allosteric modulation
B) covalent modification
C) changing the enzyme concentration
D) All of the above are usually equally as fast

Question 12

Ten people are sitting in a row. Their objective is to whisper a secret from one person to the next all the way down the row. The first person whispers the secret to the second person who passes the secret to the third person and so on. After whispering to the third person, the second person in the row notices the ninth person has fallen asleep in their chair, so she gets up, goes down the row and shakes person nine awake. This example is similar to .

A) allosteric control
B) positive cooperativity
C) feed-forward activation
D) negative modulation

Question 13

An organism that uses organic molecules as carbon sources and obtains energy by oxidizing inorganic molecules is aan) .

A) photoautotroph
B) chemoautotroph
C) photoheterotroph
D) chemoheterotroph

Question 14

The glycolytic pathway oxidizes glucose to two molecules of pyruvate and also produces a net of two molecules of ATP. ATP allosterically inhibits the enzyme, PFK-1, that catalyzes the third step of glycolysis. This is an example of .

A) feed-forward activation
B) feedback inhibition
C) negative cooperativity
D) competitive inhibition

Question 15

A distinct set of metabolic reactions is called a reaction .

A) network
B) cycle
C) pathway
D) mechanism

Question 16

The most biochemically complex organisms are .

A) chemoheterotrophs
B) photoheterotrophs
C) heterotrophs
D) autotrophs

Question 17

The evolution of biochemical pathways can be studied by

A) isolating pathway enzymes from different individuals.
B) comparing pathways in closely related species.
C) comparing pathways in many diverse bacteria.
D) comparing linear and circular pathways.

Question 18

The degradation of which class of biochemicals does not significantly contribute to the release of energy to cells?

A) nucleic acids
B) proteins
C) lipids
D) carbohydrates

Question 19

Which statement does not explain why many biochemical processes are carried out via multi-step pathways rather than by single-step reactions or only a few steps)?

A) Multi-step pathways allow for more control points to regulate biochemical processes.
B) The end products of most pathways can usually be produced only by the pathway reactions that nature has evolved.
C) Sharing of intermediates between pathways is facilitated this way.
D) There is greater control over the amounts of energy that are consumed or released at any one time.

Question 20

Which statement is not true about catabolic pathways?

A) They have a net release of energy.
B) They have a net consumption of ATP.
C) They liberate smaller molecules from larger ones.
D) They include the citric acid cycle.

Question 21

Which statement is false about ATP?

A) Its concentration in a particular cell usually fluctuates very little.
B) The concentration of ATP in cells is generally much lower than that of AMP.
C) Its concentration is maintained in part by adenylate kinase.
D) The intracellular concentration of ATP varies among cell types.

Question 22

Fatty acid synthesis occurs in the , while fatty acid breakdown occurs in the .

A) cytosol; mitochondria
B) cytosol; nucleus
C) mitochondria; cytosol
D) Golgi apparatus; cytosol

Question 23

The ultimate product of complete oxidation of carbohydrates is .

A) carbon dioxide
B) acetyl CoA
C) pyruvate
D) acetate ion

Question 24

Which of the following is not a factor contributing to the large free energy of hydrolysis of ATP?

A) Electrostatic repulsion of oxygen atoms
B) Better solvation of products than ATP itself
C) Complexes with Mg²⁺ or Mn²⁺ ions
D) Better stability of products than ATP itself
E) Electrical shielding of products of hydrolysis

Question 25

Levels of ATP and ADP are partly maintained in cells by

A) phosphoglucomutase.
B) the ADP concentration.
C) adenylate kinase.
D) and equilibrium with dissolved oxygen.

Question 26

The amount of energy recovered as ATP can be estimated by measuring free energy of hydrolysis of

A) phosphoester bond in ATP.
B) phosphoanhydride bonds in ADP.
C) phosphoester bond ADP.
D) phosphoanhydride bonds in ATP.
E) All of the above

Question 27

Which are membrane associated pathways?

A) electron transport chain in eukaryotes
B) citric acid cycle in bacteria
C) photosynthesis
D) glycolysis
E) Both A and C above

Question 28

Calculate △G°^ʹ for the reaction shown if the mass action ratio, Q, is 5.3 × 10² M^-1 and △G is 46 kJ/mol at a temperature of 298 K. R = 8.315 J/K-mol) ADP + P_i ⇌ ATP

A) 30 kJ/mol
B) -30 kJ/mol
C) 61 kJ/mol
D) -61 kJ/mol

Question 29

The conversion of glucose-1-phosphate to glucose-6-phosphate by the enzyme phosphoglucomutase has a △G°^ʹ of -7.6 kJ/mol. Calculate the equilibrium constant for this reaction at 298 K and a pH of 7. R = 8.315 J/K-mol)

A) 0.003
B) 0.047
C) 1.00
D) 21

Question 30

Nucleoside triphosphates exist in a cell as complexes with

A) Phosphate ion.
B) Mg²⁺ only.
C) Mn²⁺ only.
D) Mg²⁺ and sometimes Mn²⁺.
E) All of the above

Question 31

A reaction that best serves as a control point for regulation .

A) is a near equilibrium reaction
B) has a large positive △G
C) is metabolically irreversible
D) follows Michaelis-Menten kinetics

Question 32

A chemical reaction with a negative enthalpy change and a negative entropy change .

A) must be spontaneous
B) must be nonspontaneous
C) could be either spontaneous or nonspontaneous depending on the temperature
D) is not possible

Question 33

The free energy for ATP hydrolysis in vivo is actually greater than the standard free energy change of -30 kJ mol^-1 because

A) it has stronger electrostatic repulsion.
B) of the actual concentrations of ATP and its hydrolysis products in cells.
C) it can easily be formed from other nucleotide triphosphates.
D) it can participate in phosphoryl group transfers.
E) All of the above

Question 34

Which thermodynamic quantity is used to determine if a reaction in a cell is spontaneous?

A) △G°^ʹ
B) △G
C) △H
D) △S

Question 35

ATP is classified as an energy-rich compound because

A) it complexes with Mg²⁺.
B) it has a relatively low free energy of hydrolysis.
C) its complete oxidation to carbon dioxide releases a large amount of energy.
D) of the free energy released from cleavage of the phosphoanhydride bond.

Question 36

Anabolic and catabolic reactions in eukaryotes can occur simultaneously in cells. This is possible because .

A) they all occur in the cytosol
B) the anabolic and catabolic pathways do not share any intermediate metabolites
C) of the compartmentation of metabolites for the reactions of opposing pathways
D) all catabolic reactions are exergonic and all anabolic reactions are endergonic

Question 37

The hydrolysis of ATP to ADP has a △G°^ʹ of -30 kJ/mol. If in an E. coli cell the concentrations of ATP, ADP and inorganic phosphate are 7.90 mM, 1.04 mM and 7.9 mM, respectively, which statement is true about the hydrolysis of ATP in the cell? Assume a temperature of 298 K. R = 8.315 J/K-mol)

A) Hydrolysis can proceed spontaneously.
B) The hydrolysis is at equilibrium.
C) The formation of ATP from ADP is occurring more rapidly than the hydrolysis.
D) The hydrolysis is being allosterically controlled.

Question 38

What defines a near-equilibrium reaction?

A) Q is close to K_eq
B) DE^0ʹ = 0
C) the reaction is a closed system with no flux in or out of the system
D) pH is approximately equal to pK_eq

Question 39

In order for a reaction to proceed spontaneously from left to right as written

A) ATP must be involved in the reaction.
B) a common intermediate must be formed.
C) the overall free-energy change must be negative.
D) a phosphate group must be transferred.
E) All of the above

Question 40

Compartmentation of enzymes

A) helps prevent loss by diffusion.
B) keeps separate pools of metabolites in cells.
C) can help control metabolic pathways.
D) All of the above

Question 41

If the standard reduction potential of a certain half-reaction is -0.30 V, which statement below is true for this half-reaction to proceed as a reduction?

A) This half-reaction will proceed if it is coupled to another half-reaction that has a standard reduction potential greater than +0.30 V.
B) This half-reaction will proceed if it is coupled to another half-reaction that has a standard reduction potential greater than -0.30 V.
C) This half-reaction will proceed if it is coupled to another half-reaction that has a standard reduction potential less than -0.30 V.
D) It doesnʹt matter what half-reaction this is coupled with, it will proceed spontaneously.

Question 42

Thioesters are similar to oxygen esters of carboxylic acids except that

A) the energy associated with their hydrolysis is much less than that of the phosphoanhydride in ATP.
B) they are more stable at neutral pH values in cells.
C) they are less stable because S is present instead of O in the linkage.
D) they are used in glycolysis and the citric acid cycle.
E) they are not hydrolyzed enzymatically.

Question 43

The formation of acetyl CoA is driven to completion by

A) the negative standard free energy for the first step of the reaction.
B) the negative standard free energy for the final step of the reaction.
C) removal of the product pyrophosphate by the enzyme pyrophosphatase.
D) the negative free energy for the formation of an ADP intermediate.
E) All of the above

Question 44

The biochemical reactions that degrade molecules, such as nutrients, are called anabolic reactions.

Question 45

Mutant organisms can be helpful in the study of metabolism because

A) one can compare the mutant to a non-mutant organism.
B) there may be an indication of a natural role for an enzyme.
C) there may be accumulations of products prior to defective enzymes.
D) the structures of enzymes may be deduced.
E) All of the above

Question 46

ATP can be used to activate a substrate by

A) phosphorylation.
B) adding a nucleotidyl group.
C) producing inorganic phosphate.
D) Both A and B

Question 47

The chemical energy generated by oxidation reactions cannot be captured by

A) NADH.
B) NADP.
C) FMN.
D) FAD.
E) Q.

Question 48

In theory at least, the energy released by the oxidation of one molecule of NADH is sufficient to form ATP molecules).

A) 0.5 meaning it takes about 2 NADH to form 1 ATP)
B) 1
C) several
D) about 20
E) about 50

Question 49

Studies of specific enzymes in cells may not give information about cell metabolism since

A) it is difficult to label many enzymes.
B) the pathways are too complex.
C) many enzymes are mutant ones.
D) conditions in isolation may not be like those inside the cell.
E) All of the above

Question 50

Calculate the equilibrium constant for an oxidation-reduction reaction involving the transfer of 1 mole of electrons with DE^0ʹ= 0.25 V. R = 8.315 JK^-1mol^-1, F = 96.48 kJV^-1mol^-1, T = 298 K)

A) 1
B) 6 x 10^-5
C) 1.7 x 10⁴
D) 0.49

Question 51

The ability and capacity of coenzymes to become oxidized or reduced reduction potential) may be found by

A) measuring the flow of zinc and copper electrons.
B) measuring the flow of electrons when compared to hydrogen gas at standard conditions.
C) measuring the number of H atoms present.
D) All of the above

Question 52

Metabolic pathways generally have easily distinguished starting and stopping points.

Question 53

ATP is thermodynamically suited as a carrier of phosphoryl groups in animal cells because

A) it is stable under cell conditions.
B) it is not hydrolyzed in cells without enzyme action.
C) it is intermediate in group-transfer potential.
D) it can be produced from phosphocreatine.
E) All of the above

Question 54

g-Glutamyl phosphate is formed as an intermediate in the conversion of glutamate to glutamine by the enzyme glutamine synthetase because

A) it has a large negative free energy.
B) it is positively charged.
C) it is unstable in water.
D) it is a nucleophile.
E) All of the above

Question 55

A given cell type tends to maintain relatively constant internal concentrations of inorganic ions, enzymes and metabolites.

Question 56

The standard potential for electron transfer can be related to the standard free-energy change for redox reactions by using

A) a calorimeter.
B) an electrochemical cell.
C) two solutions separated by a salt bridge.
D) the Nernst equation.
E) the Faraday equation.

Question 57

Phosphatases catalyze the hydrolytic removal of phosphate groups.

Question 58

Which compound has a greater free energy of hydrolysis than ATP?

A) glucose 1-phosphate
B) any phosphoester
C) phosphoenolpyruvate
D) acetyl CoA
E) All of the above

Question 59

Most metabolic reactions occur continuously at a fixed rate.

Question 60

When a reduction half-reaction is negative, positive), electrons flow to the more readily reduced substance which is negative, positive) in value.

A) negative; negative
B) negative; positive
C) positive; positive
D) positive; negative

Question 61

Phosphorylation of enzymes involved in catabolic pathways usually activates them.

Question 62

ATP is thermodynamically suited as a carrier of phosphoryl groups because it has one of the highest phosphoryl-group-transfer potentials in cells.

Question 63

The presence of Mg²⁺ ions decreases the free energy released by the hydrolysis of ATP.

Question 64

Phosphagens are energy-rich phosphoanhydrides found in animal muscle cells and which have higher group-transfer potentials than ATP.

Question 65

The phosphoester bond and phosphoanhydride bonds in ATP have the approximately same free energies of hydrolysis.

Question 66

Reactions of most metabolic pathways are in a state of equilibrium and have a △G equal to zero.

Question 67

The process of dissolving table salt, NaCl, in water involves an increase in entropy.

Question 68

It would be possible for cells to couple glutathione reduction E° = -0.23) to the oxidation of cytochrome c₁ E°^ʹ = 0.23).

Question 69

The synthesis of acetyl CoA shows that another important role for ATP in cells is to provide its nucleotidyl group for transfer in metabolism.

Question 70

By linking a reaction that would not ordinarily proceed to the hydrolysis of ATP, the overall coupled reaction may be completed.

Question 71

ATP has the highest possible standard free energy of hydrolysis in cells; therefore it is the most energy-rich compound in living systems.

Question 72

All metabolic reactions occur in the cytosol of cells.

Question 73

Many dehydrogenases can be assayed by measuring the decrease of absorption of NAD⁺ or the increase of absorption of NADH.

Question 74

Although the CoA thioester is less stable than oxygen esters, it is stable in cells, resisting nonenzymatic hydrolysis at neutral pH values.

Question 75

Both NADH and NADPH are oxidized in cells, but NADH is more often used in specialized pathways to provide hydride ions for reductive reactions in metabolism.