Biochem Exam 3

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until equilibrium is reached, the final mixture contains twice as much glucose 6-phosphate as fructose 6- phosphate. Which one of the following statements is best applied to this reaction outlined below? (R = 8.315 J/mol ·  K; T = 298 K)

glucose 6-phosphate → fructose 6-phosphate

ΔG'° is incalculably large and negative.

ΔG'° is –1.72 kJ/mol.

ΔG'° is zero.

ΔG'° is +1.72 kJ/mol.

ΔG'° is incalculably large and positive.

ΔG'° is +1.72 kJ/mol.

Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6- phosphatase is 99% complete at equilibrium (i.e., only 1% of the substrate remains). Which statement is MOST nearly  correct?  (R =  8.315 J/mol·K;  T =  298 K)

ΔG'° is –11 kJ/mol.

ΔG'° is –5 kJ/mol.

ΔG'° is 0 kJ/mol.

ΔG'° is +11 kJ/mol.

ΔG'° cannot be determined from the information given.

ΔG'° is –11 kJ/mol.

The reaction A + B → C has a ΔG'° of –20 kJ/mol at 25° C. Starting under standard conditions, one can predict that:

at equilibrium, the concentration of B will exceed the concentration  of A.

at equilibrium, the concentration of C will be less than the concentration of A.

at equilibrium, the concentration of C will be much greater than the concentration of A or B.

C will rapidly break down to A + B.

when A and B are mixed, the reaction will proceed rapidly toward formation of C.

at equilibrium, the concentration of C will be much greater than the concentration of A or B.

Which compound has the LARGEST negative value for the standard free- energy change(ΔG'°) upon hydrolysis?

acetic anhydride

glucose 6-phosphate

glutamine

glycerol 3-phosphate

lactose

acetic anhydride

If the ΔG'° of the reaction A → B is –40 kJ/mol, under standard conditions the reaction:

is at equilibrium.

will never reach equilibrium.

will not occur spontaneously.

will proceed at a rapid rate.

will proceed spontaneously from A to B.

will proceed spontaneously from A to B.

For the reaction A → B, ΔG'° = –60 kJ/mol. The reaction is started with

10 mmol of A; no B is initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A.  Which statement is the MOST likely explanation?

A and B have reached  equilibrium concentrations.

An enzyme has shifted the equilibrium toward A.

B formation is kinetically slow; equilibrium has not been reached by 24 hours.

Formation of B is thermodynamically unfavorable.

The result described is  impossible, given the fact that ΔG'° is –60 kJ/mol.

B formation is kinetically slow; equilibrium has not been reached by 24 hours.

When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25 °C with phosphoglycerate mutase until equilibrium is reached, the final mixture contains six times as much 2-phosphoglycerate as 3-phosphoglycerate.

Which statement is MOST nearly correct, when applied to the reaction as written? (R = 8.315 J/mol · K; T =298 K)

3-phosphoglycerate → 2-phosphoglycerate

ΔG'° is –4.44 kJ/mol.

ΔG'° is zero.

ΔG'°is +12.7 kJ/mol.

ΔG'°is incalculably large and positive.

ΔG'° cannot be calculated from the information given.

ΔG'° is –4.44 kJ/mol.

For the following reaction, ΔG'° = +29.7 kJ/mol.

L-Malate + NAD+ → oxaloacetate + NADH + H+

The reaction as written:

can never occur in a cell.

can occur in a cell only if it is coupled to another reaction for which ΔG'° is positive.

can occur only in a cell in which NADH is converted to NAD+ by electron transport.

cannot occur because of its large activation energy.

may occur in cells at some concentrations of substrate and product.

may occur in cells at some concentrations of substrate and product.

For the reaction A → B, the Keq' is 104. If a reaction mixture originally contains 1mmol of A and no B, which statement must be TRUE?

At equilibrium, there will be far more B than A.

The rate of the reaction is very slow.

The reaction requires coupling to an exergonic reaction in order to proceed.

The reaction will proceed toward B at a very high rate.

ΔG'° for the reaction will be large and positive.

At equilibrium, there will be far more B than A.

For the reaction A → B, the Keq' is 10–6. If a reaction mixture originally contains 1mmol of A and 1 mmol of B, which statement must be TRUE?

At equilibrium, there will still be equal levels of A and B.

The rate of the reaction is very slow.

At equilibrium, the amount of A will greatly exceed the amount of B.

The reaction will proceed toward B at a very high rate.

ΔG'° for the reaction will be large and positive.

At equilibrium, there will still be equal levels of A and B.

In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (ΔG'°) of 23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (ΔG) be negative, enabling the reaction to proceed spontaneously to the right?

Under standard conditions, enough energy is released to drive the reaction to the right.

The reaction will not go to the right spontaneously under any conditions because the ΔG'° is positive.

The reaction will proceed spontaneously to the right if there is a high concentrations of products relative to the concentration of fructose 1,6-bisphosphate.

The reaction will proceed spontaneously to the right if there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

None of these conditions is sufficient.

Under standard conditions, enough energy is released to drive the reaction to the right.

During glycolysis, glucose 1-phosphate is converted to fructose 6-phosphate in two successive reactions:

glucose 1-phosphate → glucose 6-phosphate ΔG'° = –7.1 kJ/mol glucose 6-phosphate → fructose 6-phosphate ΔG'° = +1.7 kJ/mol

ΔG'° for the overall reaction is:

–8.8 kJ/mol.

–7.1 kJ/mol.

–5.4 kJ/mol.

+5.4 kJ/mol.

+8.8 kJ/mol

–5.4 kJ/mol.

The standard free-energy changes for the reactions below are given.

phosphocreatine → creatine + Pi ΔG'° = –43.0 kJ/mol

ATP → ADP + Pi ΔG'° = –30.5 kJ/mol

What is the overall ΔG'° for the following reaction?

phosphocreatine + ADP  → creatine + ATP

–73.5 kJ/mol

–12.5 kJ/mol

+12.5 kJ/mol

+73.5 kJ/mol

ΔG'° cannot be calculated without Keq'.

–12.5 kJ/mol

The ΔG'° values for the two reactions shown below are given.

oxaloacetate + acetyl-CoA + H2O → citrate + CoASH ΔG'° = –32.2 kJ/mol

oxaloacetate + acetate → citrate ΔG'° = –1.9 kJ/mol

What is the ΔG'° for the hydrolysis of acetyl-CoA?

Acetyl-CoA + H2O → acetate + CoASH + H+

–34.1 kJ/mol

–32.2 kJ/mol

–30.3 kJ/mol

+61.9 kJ/mol

+34.1 kJ/mol

–30.3 kJ/mol

Which item is NOT nucleophilic?

a proton

a carbanion

an imidazole

a hydroxide

a carboxylic acid

a proton

Which item is NOT electrophilic?

a proton

a sulfhydryl

a protonated imine

a carbonyl group

a phosphoryl group

a sulfhydryl

Which statement is NOT true?

The carbon adjacent to a carbonyl can be resonance stabilized to form a carbanion.

A carbonyl carbon can be made more electrophilic by a nearby metal ion.

The carbon adjacent to an imine can be resonance stabilized to form a carbanion

Decarboxylation of an α-keto acid goes through a carbocation intermediate.

A Claisen ester condensation reaction goes through a carbanion intermediate.

Decarboxylation of an α-keto acid goes through a carbocation intermediate.

The reaction ATP → ADP  + Pi is an example of a(n) ___ reaction.

homolytic cleavage

internal rearrangement

free radical

group transfer

oxidation/reduction

group transfer

Which statement is TRUE about oxidation-reduction reactions?

They usually proceed through homolytic cleavage.

During oxidation a compound gains electrons.

Dehydrogenases typically remove two electrons and two hydrides.

There are four commonly accessed oxidation states of carbon.

Every oxidation must be accompanied by a reduction.

Every oxidation must be accompanied by a reduction.

Which factor does NOT contribute to the large, negative, free-energy change upon hydrolysis of high-energy compounds?

electrostatic repulsion in the reactant

low activation energy of forward reaction

stabilization of products by extra resonance forms

stabilization of products by ionization

stabilization of products by solvation

low activation energy of forward reaction

The hydrolysis of ATP has a large negative ΔG'°; nevertheless it is stable in solution due to:

entropy stabilization.

ionization of the phosphates.

resonance stabilization.

the hydrolysis reaction being endergonic.

the hydrolysis reaction having a large activation energy.

the hydrolysis reaction having a large activation energy.

The hydrolysis of phosphoenolpyruvate proceeds with a ΔG'° of about –62 kJ/mol. The greatest contributing factors to this reaction are the destabilization of the reactants by electrostatic repulsion and stabilization of the product pyruvate by:

electrostatic attraction.

ionization.

polarization.

resonance.

tautomerization.

tautomerization.

Which compound(s) do(es) NOT have a large negative free energy of hydrolysis?

1,3-bis phosphoglycerate

3-phosphoglycerate

ADP

phosphoenolpyruvate

thioesters (e.g., acetyl-CoA)

3-phosphoglycerate

The immediate precursors of DNA and RNA synthesis in the cell all contain:

3′ triphosphates.

5′ triphosphates.

adenine.

deoxyribose.

ribose.

5′ triphosphates.

Muscle contraction involves the conversion of:

chemical energy to kinetic energy.

chemical energy to potential energy.

kinetic energy to chemical energy.

potential energy to chemical energy.

potential energy to kinetic energy.

chemical energy to kinetic energy.

Biological oxidation-reduction reactions always involve:

direct participation of oxygen.

formation of water.

mitochondria.

transfer of electron(s).

transfer of hydrogens.

transfer of electron(s).

Biological oxidation-reduction reactions never involve:

transfer of e- from one molecule to another.

formation of free e–.

transfer of H+  (or H3O+) from one molecule to another.

formation of free H+ (or H3O+).

None of the answers is correct.

formation of free e–.

The standard reduction potentials (E'°) for the following half reactions are given.

fumarate + 2H+ + 2e– → succinate E'° = +0.031 V

FAD + 2H+ + 2e–  → FADH2 E'° = –0.219 V

If you mixed succinate, fumarate, FAD, and FADH2 together, all at 1M concentrations and in the presence of succinate dehydrogenase, what would happen initially?

Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced.

Fumarate would become reduced; FADH2 would become oxidized.

No reaction would occur because all reactants and products are already at their standard concentrations.

Succinate would become oxidized; FAD would become reduced.

Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor.

Fumarate would become reduced; FADH2 would become oxidized.

E'° of the NAD+/NADH half reaction is –0.32 V. The E'° of the oxaloacetate/malate half reaction is –0.175 V. When the concentrations of NAD+, NADH, oxaloacetate, and malate are all 10^–5 M, the spontaneous reaction is:

malate + NAD+ → oxaloacetate +  NADH + H+.

malate + NADH  + H+ →  oxaloacetate + NAD+.

NAD+ + NADH + H+ → malate  + oxaloacetate.

NAD+ + oxaloacetate → NADH + H+ + malate.

oxaloacetate + NADH + H+ → malate + NAD+.

oxaloacetate + NADH + H+ → malate + NAD+.

The structure of NAD⁺ does NOT include:

a flavin nucleotide.

a pyrophosphate bond.

an adenine nucleotide.

nicotinamide.

two ribose residues.

a flavin nucleotide.

Which statement is NOT true for the nicotinamide cofactors?

The oxidized form is positively charged.

The reduced form has a large extinction coefficient at  340 nm.

The oxidized form provides reducing equivalents to other molecules.

Oxidation-reduction reactions with nicotinamides usually involve hydride transfer.

Enzymes transfer hydrides stereospecifically to one or the other side of the nicotinamide ring.

The oxidized form provides reducing equivalents to other molecules.

Which amino acid can participate in nucleophilic catalysis?

His

Cys

Tyr

All of the answers are correct.

None of the answers is correct.

All of the answers are correct.

Which atom is a common electrophile?

a hydrogen atom

an oxygen  atom of a carbonyl group

an oxygen atom of a phosphate group

All of the answers are correct.

None of the answers is correct.

None of the answers is correct.

Which atom is a possible nucleophile?

an oxygen atom in a hydroxide ion

an oxygen atom of a carboxylate group

a nitrogen atom of a deprotonated amine

All of the answers are correct.

None of the answers is correct.

All of the answers are correct.

Which statement is always TRUE for ΔG'?

The temperature is 25°C.

The pH is 7.0.

The value for ΔG' is a constant.

The initial concentration of each component is 1.0 M.

The pressure is 1 atm.

The pH is 7.0.

ΔG'° for the hydrolysis of ATP is –30.5 kJ/mol. What effect will doubling ATP concentration have on the value of ΔG'° for ATP hydrolysis?

Make the value of ΔG'° more negative.

Make the value of ΔG'°  less negative.

There will be no change in the value of ΔG'°.

Make the value of ΔG'° more positive.

Make the value of ΔG'°  less positive.

There will be no change in the value of ΔG'°.

Which carbon atom is in the MOST oxidized state?

a carbon in an alkyl group

a carbon in a ketone group

a carbon in carbon dioxide

a carbon in a carboxylic acid group

a carbon in an alcohol group

a carbon in carbon dioxide

Which is the MOST oxidized carbon atom in a ketohexose sugar?

C1

C2

C3

C5

C6

C2

Which carbon atom is in the MOST reduced state?

a carbon in an alkyl group

a carbon in an aldehyde group

a carbon in a ketone group

a carbon in a carboxylic acid group

a carbon in an alcohol group

a carbon in an alkyl group

Which compound is classified as high energy?

phosphoarginine

succinyl-CoA

fatty acid-CoA

All of the answers are correct.

None of the answers is correct.

All of the answers are correct.

What is the equilibrium constant for a reaction with a standard free-energy change of +25kJ/mol?

–1.1

–10.1

4.1 × 10^–5

10.1

2.4 × 10⁴

4.1 × 10^–5

What is the equilibrium constant for the reaction shown below?glutathione + NADPH + H⁺ ↔ reduced glutathione + reduced glutathione + NADP⁺

0.073

1.073

7.03

17.4

1,487

1,487

What is the ΔG'° for the following reaction if the concentrations of glucose-6-phosphate and glucose-1-phosphate at equilibrium are 19 mM and 1 mM, respectively?

glucose-6-phosphate ↔ glucose-1-phosphate

7.3 kJ/mol

7.6 kJ/mol

–7.3 kJ/mol

–7.6 kJ/mol

ΔG'° cannot be determined from the information given.

7.3 kJ/mol

In the following reaction, which molecule is the reductant?

1,3-bisphosphoglycerate + NADH +  H⁺ ↔ glyceraldehyde-3-phosphate + Pi + NAD⁺

1,3-bisphosphoglycerate

NADH

H+

glyceraldehyde-3-phosphate

both NADH and glyceraldehyde-3-phosphate

both NADH and glyceraldehyde-3-phosphate

In the following reaction, which molecule is the oxidant?

1,3-bisphosphoglycerate + NADH +  H⁺ → glyceraldehyde-3-phosphate + Pi + NAD⁺

1,3-bisphosphoglycerate

NADH

H+

glyceraldehyde-3-phosphate

NAD+

1,3-bisphosphoglycerate

In the following reaction, which molecule is the reducing agent?

glyceraldehyde-3-phosphate + Pi + NAD⁺ →  1,3-bisphosphoglycerate +  NADH + H⁺

1,3-bisphosphoglycerate

NADH

H+

glyceraldehyde-3-phosphate

NAD+

glyceraldehyde-3-phosphate

Which molecule is NOT considered a universal electron carrier?

NADH

ATPF

ADH2

FMNH2

both ATPF and FMNH2

ATPF

Under standard conditions, is the oxidation of NADH by free FAD sufficiently exergonic to drive the synthesis of ATP?

no, as oxidation of NADH by FAD only generates  –9.65 kJ/mol

no, as oxidation of NADH by FAD only generates  –19.3 kJ/mol

no, as oxidation of NADH by FAD only generates 9.65 kJ/mol

no, as oxidation of NADH by FAD only generates 19.3 kJ/mol

yes, as oxidation of NADH by FAD generates  –104.2 kJ/mol

no, as oxidation of NADH by FAD only generates  –19.3 kJ/mol

Under standard conditions, is the oxidation of free FADH2 by ubiquinone sufficiently exergonic to drive the synthesis of ATP?

no,as oxidation of FADH2 by ubiquinone generates 33.6 kJ/mol

no, as oxidation of FADH2 by ubiquinone generates 50.9 kJ/mol

no, as oxidation of FADH2 by ubiquinone generates  –25.5 kJ/mol

yes, as oxidation of FADH2  by ubiquinone generates –33.6 kJ/mol

yes, as oxidation of FADH2  by ubiquinone generates –50.9 kJ/mol

yes, as oxidation of FADH2  by ubiquinone generates –50.9 kJ/mol

Which atom is the LEAST electronegative?

C

N

H

O

S

H

Which atom is the MOST electronegative?

C

N

P

O

S

O

Which statement is FALSE regarding biological oxidations?

The redox potential is the affinity of a substance to accept electrons.

Oxidation can occur by addition of oxygen to a molecule.

Electrons are transferred from substances with a high reduction potential to substances with a lower reduction potential.

Oxidases, oxygenases, and dehydrogenases are all enzymes that catalyze biological oxidation reactions.

NAD+ is a cosubstrate of certain dehydrogenases and always accepts electrons in the form of hydride ions.

Electrons are transferred from substances with a high reduction potential to substances with a lower reduction potential.

Which statement about NAD+ and NADH is FALSE?

NAD+ is oxidized to NADH by α-ketoglutarate dehydrogenase.

Lactate dehydrogenase binds NAD+ tightly in the Rossmann fold.

NAD+ accepts both electrons as a hydride ion.

NAD+ is oxidized to NADH by α-ketoglutarate dehydrogenase, and lactate dehydrogenase binds NAD+ tightly in the Rossmann fold.

NAD+ is oxidized to NADH by α-ketoglutarate dehydrogenase, and NAD+ accepts both electrons as a hydride ion.

NAD+ is oxidized to NADH by α-ketoglutarate dehydrogenase, and lactate dehydrogenase binds NAD+ tightly in the Rossmann fold.

The phosphate bonds found in a phosphorylated tyrosine and in an acyl phosphate are likely to have similar standard free energies of hydrolysis.

true

false because hydrolysis of a phosphorylated tyrosine would release significantly more energy than hydrolysis of an acyl phosphate.

false because hydrolysis of an acyl phosphate would release significantly more energy than hydrolysis of a phosphorylated tyrosine

false because hydrolysis of an acyl phosphate would release significantly more energy than hydrolysis of a phosphorylated tyrosine

Which statement is NOT true regarding the biochemical standard state?

The [H+] is  10–7M.

Temperature is 28°C.

All reactants and products are present at 1 M concentrations.

The pressure  is 1 atm.

The concentration of water is essentially constant at 55.5 M.

Temperature is 28°C.

What is the CORRECT order of substances in terms of electronegativity, greatest to least?

H → C → N → S → O

H → C → S → O → N

O → S → N → C → H

N → O → S → H → C

O → N → S → C → H

O → N → S → C → H

Which statement is FALSE regarding carbonyl groups?

The carbon atom in a carbonyl group is more oxidized than the carbon atom in carbon dioxide.

The carbon atom of a carbonyl group is an electrophile.

Electron delocalization by a carbonyl group stabilizes an adjoining carbanion, thus facilitating its formation.

Positively charged metal ions may enhance the ability of a carbonyl group to act as an electron sink.

The functional group of aldehydes and ketones is a carbonyl group.

The carbon atom in a carbonyl group is more oxidized than the carbon atom in carbon dioxide.

If the equilibrium constant for the dissociation of lactic acid is 1.38 × 10^–4, what is the ΔG°' for this reaction?

16.3kJ/mol

–16.3 kJ/mol

16.96 kJ/mol

–16.96 kJ/mol

27.5 kJ/mol

16.3kJ/mol

Which statement is TRUE?

The rate of a reaction that generates NAD+ can be determined by measuring the rate of increase in absorbance at 340 nm.

NADH and NADPH are classified as pyrimidine nucleotides due to the presence of the nicotinamide ring which resembles pyrimidine.

NAD+ has a net charge of +1.

In many cells, the ratio of NADP+ to NADPH is high favoring the reduction of biomolecules.

A phosphoanhydride bond links the two nucleotides in nicotinamide dinucleotides.

A phosphoanhydride bond links the two nucleotides in nicotinamide dinucleotides.

Which biochemical reaction is NOT used in the process of activating a biological molecule?

Phosphoryl group transfer from ATP forming a new phosphoester linkage.

Formation of a thioester bond by linking a molecule to coenzyme A.

Pyrophosphoryl group transfer from ATP forming a new phosphodiester linkage.

Adenylyl transfer from ATP by forming a new phosphodiester linkage.

All these reactions may be involved.

Pyrophosphoryl group transfer from ATP forming a new phosphodiester linkage.

Under cellular conditions (37°C), what is the actual free energy for the reaction shown below when the ratio of glucose-6-phosphate to fructose-6- phosphate is 0.8:0.2?

glucose-6-phosphate ↔ fructose-6-phosphate ΔG′° = 1.7 kJ/mol

1730 kJ/mol

1870 KJ/mol

1.73 kJ/mol

–1.73 kJ/mol

–1.87 kJ/mol

–1.87 kJ/mol

Which phosphorylated amino acid is used by invertebrates in a similar manner that invertebrates use phosphocreatine?

phosphocysteine

phosphoarginine

phosphohistidine

phosphoaspartate

phosphotyrosine

phosphoarginine

Which statement is TRUE regarding coupled reactions?

The standard free energy changes of the coupled reactions are additive, and their equilibrium constants are multiplicative.

The coupled reactions must share a common intermediate.

The free energy of the endergonic reaction must be greater in magnitude than the free energy of the exergonic reaction.

The standard free energy changes of the coupled reactions are additive, their equilibrium constants are multiplicative, and the coupled reactions must share a common intermediate.

None of the statements is true.

The standard free energy changes of the coupled reactions are additive, their equilibrium constants are multiplicative, and the coupled reactions must share a common intermediate.

Which statement is TRUE regarding the actual free-energy change for a reaction?

The actual free-energy change varies depending on the pathway by which the reaction occurs.

When the standard free energy is large and positive, the reaction will never occur.

The actual free energy varies depending on the standard free energy and the concentration of reactants and products.

All of the statements are true.

None of the statements is true.

The actual free energy varies depending on the standard free energy and the concentration of reactants and products.

Which statement about Gibbs free energy is FALSE?

At equilibrium, the actual free energy  is zero and ΔG′° = –RTln Keq

When the reactants are in excess of their equilibrium concentrations, the conversion of product to reactant is more likely to occur.

The standard free energy of a redox reaction can be determined if the standard reduction potentials of both the products and reactants are known.

All of the statements are false.

None of the statements is false.

When the reactants are in excess of their equilibrium concentrations, the conversion of product to reactant is more likely to occur.

Which conjugate redox pair is involved in biological oxidations?

Fe²⁺ and Fe³⁺

NADP⁺ and NAD⁺

FMN and FADH2

succinate and fumarate

both Fe²⁺ and Fe³⁺ and succinate and fumarate

both Fe²⁺ and Fe³⁺ and succinate and fumarate

Which statement is TRUE for the equilibrium constant?

The equilibrium constant is independent of the initial concentrations of reactants and products.

When the equilibrium constant is greater than one, the standard free energy change for the reaction favors production of reactants.

The equilibrium constant does not vary with changes in pH.

The equilibrium constant does not vary with changes in temperature.

A relatively small change in the equilibrium constant is associated with a large change in the standard free-energy change.

The equilibrium constant is independent of the initial concentrations of reactants and products.

Which enzyme catalyzes phosphate transfer reactions between nucleotides?

nucleoside diphosphate kinase

creatine kinase

adenylate kinase

both nucleoside diphosphate kinase and adenylate kinase

both creatine kinase and adenylate kinase

both nucleoside diphosphate kinase and adenylate kinase

Under standard conditions, ATP can be used in phosphate-transfer reactions to generate which molecule?

phosphocreatine

glycerol-3-phosphate

phosphoenolpyruvate

1,3-bisphosphoglycerate

All of the answers are correct.

glycerol-3-phosphate

Which statement regarding redox reactions is TRUE?

NADH and FADH2 are major electron acceptors in the oxidation of fuel molecules.

In glycolysis, the conversion of 2-phosphpoglycerate to phosphoenolpyruvate is a redox reaction.

In a redox reaction, the oxidation state of the substrate remains unchanged.

A redox reaction is spontaneous when the substrate has a greater reduction potential than the product.

The Nernst equation relates the standard reduction potential of a redox pair to its actual reduction potential at any concentration of either the oxidized or reduced form of the species.

The Nernst equation relates the standard reduction potential of a redox pair to its actual reduction potential at any concentration of either the oxidized or reduced form of the species.

____ is used to illustrate the actual free-energy change of a reaction measured at pH 7and 37°C.

ΔG

ΔG′

ΔG′°

ΔG°′

ΔG°

ΔG′

Which statement is TRUE regarding ΔG′?

ΔG′  is negative when the reaction is occurring spontaneously.

ΔG′ is zero when the rate of the forward and reverse reactions are equal.

ΔG′ becomes less negative as the reaction proceeds spontaneously.

All of the statements are true.

None of the statements is true.

All of the statements are true.

Which statement is TRUE with respect to the change in free energy for a given reaction?

ΔG is linearly proportional to the rate of the reaction.

ΔG is a logarithmic function of the equilibrium constant.

ΔG provides no information about the rate of the reaction.

All of the statements are true.

None of the statements is true.

ΔG provides no information about the rate of the reaction.

ATP can be generated from a variety of phosphorylated compounds via phosphate-transfer reactions. Which molecules CANNOT serve as high-energy phosphate donors in the synthesis of ATP?

phosphate esters

acyl phosphates

phosphagens

phosphoamides

enolphosphates

phosphate esters

Which redox reaction(s) will NOT proceed as written if the initial concentrations of reactants and products are equal?

pyruvate + NADH →  lactate + NAD⁺

FADH² + NAD⁺ → FAD +  NADH + H⁺

succinate + NAD⁺ → fumarate + NADH  + H⁺

NADH +  H⁺ + ubiquinone → NAD⁺ + ubiquinol

cytochrome c-Fe³⁺ + cytochrome b-Fe²⁺ → cytochrome c-Fe²⁺ + cytochrome b-Fe³⁺

I and IV

I, IV, and V

II

II and III

IV and V

II and III

Acyl phosphates, phosphoesters, and phosphoanhydrides are compounds of significantly different phosphoryl group-transfer potentials. Which choice CORRECTLY ranks these phosphorylated intermediates with respect to their phosphoryl group-transfer potential from highest to lowest?

1,3-bisphosphoglycerate → adenosine triphosphate → glucose 1-phosphate

glucose 1-phosphate → adenosine triphosphate → 1,3-bisphosphoglycerate

adenosine triphosphate → 1,3-bisphosphoglycerate → glucose 1-phosphate

adenosine triphosphate → glucose 1-phosphate → 1,3-bisphosphoglycerate

1,3-bisphosphoglycerate → glucose 1-phosphate → adenosine triphosphate

1,3-bisphosphoglycerate → adenosine triphosphate → glucose 1-phosphate

Which statement is TRUE for the reaction A + B ↔ C + D  if its Keq

for the reaction is 10⁴?

When the reaction has reached equilibrium, there will be significantly more A and B than C and D in solution.

The formation of A and B will proceed at a high rate.

The value of ΔG′° will be large and positive.

All of the statements are true.

None of the statements is true.

None of the statements is true.

Given that the ΔG′^o values for the hydrolysis of glucose 1-phosphate and glucose 6-phosphate are approximately –21 kJ/mol and –14 kJ/mol, respectively, which statement is TRUE regarding the following isomerizations?

glucose 1-phosphate ↔ glucose 6-phosphate

Under cellular conditions the direction of the reaction depends on the concentrations of glucose 1-phosphate and glucose 6-phosphate.

The overall rate of this reaction is relatively slow.

An increase in entropy ―drives this reaction.

The value of ΔG′^o for this  isomerization reaction is small and positive.

All the statements are true for the  isomerization reaction shown above.

Under cellular conditions the direction of the reaction depends on the concentrations of glucose 1-phosphate and glucose 6-phosphate.

Glycolysis is the name given to a metabolic pathway occurring in many different cell types. It consists of 11 enzymatic steps that convert glucose to lactic acid. Glycolysis is an example of:

aerobic metabolism.

anabolic metabolism.

a net reductive process.

fermentation.

oxidative phosphorylation.

fermentation.

The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway results in a net formation of:

1 mol of NAD+  and 2 mol of ATP.

1 mol of NADH and 1 mol of ATP.

2 mol of NAD+  and 4 mol of ATP.

2 mol of NADH and 2 mol of ATP.

2 mol of NADH and 4 mol of ATP.

2 mol of NADH and 4 mol of ATP.

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which statement is MOST nearly correct, when applied to the reaction below (R = 8.315 J/mol ·K and T = 298 K)?

glucose 6-phosphate ↔ fructose 6-phosphate

ΔG'° is +1.7 kJ/mol.

ΔG'° is –1.7 kJ/mol.

ΔG'° is incalculably large and negative.

ΔG'° is incalculably large and positive.

ΔG'° is zero.

ΔG'° is +1.7 kJ/mol.

In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (ΔG'°) of 23.8 kJ/mol. Under what conditions (encountered in a normal cell) will the free-energy change (ΔG) be negative, enabling the reaction to proceed to the right?

If the concentrations of the two products are high relative to that of fructose1,6-bisphosphate.

The reaction will not go to the right spontaneously under any conditions because the ΔG'° is positive.

Under standard conditions, enough energy is released to drive the reaction to the right.

When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

When there is a high concentration of products relative to the concentration of fructose 1,6-bisphosphate.

When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

Glucose labeled with ¹⁴C in C-1 and C-6 gives rise in glycolysis to pyruvate labeled  in:

both its carbonyl and carboxyl carbons.

all three carbons.

its carbonyl carbon.

its carboxyl carbon.

its methyl carbon.

its methyl carbon.

If glucose labeled with ¹⁴C at C-2 were metabolized in the liver, the first radioactive pyruvate formed would be labeled in:

all three carbons.

both its carbonyl and carboxyl carbons.

its carbonyl carbon.

its carboxyl carbon.

its methyl carbon.

its carbonyl carbon.

Which reaction in glycolysis requires ATP as a substrate?

hexokinase

glyceraldehyde-3-phosphate dehydrogenase

pyruvate kinase

aldolase

phosphoglycerate kinase

hexokinase

Which reaction in glycolysis produces ATP as a product?

hexokinase

glyceraldehyde-3-phosphate dehydrogenase

pyruvate kinase

aldolase

phosphofructokinase-1

pyruvate kinase

Which reaction in glycolysis is an aldose to ketose isomerization?

enolase

phosphoglycerate mutase

phosphohexose isomerase

aldolase

glyceraldehyde-3-phosphate dehydrogenase

phosphohexose isomerase

Which reaction in glycolysis is a ketose to aldose isomerization?

hexokinase

phosphoglycerate mutase

enolase

aldolase

triose phosphate isomerase

triose phosphate isomerase

Which reaction in glycolysis utilizes a covalent enzyme intermediate?

phosphofructokinase-1

hexokinase

phosphohexose isomerase

aldolase

triose phosphate isomerase

aldolase

Which reaction in glycolysis utilizes a covalent enzyme intermediate?

phosphofructokinase-1

glyceraldehyde-3-phosphate dehydrogenase

phosphohexose isomerase

enolase

triose phosphate isomerase

glyceraldehyde-3-phosphate dehydrogenase

The compound [¹⁸F]2-fluoro-2-deoxyglucose is a(n):

intermediate in glycolysis

positive regulator of glycolysis

potent anti-cancer agent

antibiotic

imaging agent used to detect tumors

imaging agent used to detect tumors

The steps of glycolysis between glyceraldehyde 3-phosphate and 3- phosphoglycerate does NOT involve:

ATP synthesis.

catalysis by phosphoglycerate kinase.

oxidation of NADH to  NAD+.

the formation of 1,3-bisphosphoglycerate.

utilization of Pi.

oxidation of NADH to  NAD+.

The first reaction in glycolysis that results in the formation of an energy- rich compound is catalyzed by:

glyceraldehyde 3-phosphate dehydrogenase.

hexokinase.

phosphofructokinase-1.

phosphoglycerate kinase.

triose phosphate isomerase.

glyceraldehyde 3-phosphate dehydrogenase

Which item is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

ATP

Cu2+

heme

NAD+

NADP+

NAD+

In the phosphoglycerate mutase reaction, the side chain of which amino acid in the enzyme is transiently phosphorylated as part of the reaction?

serine

threonine

tyrosine

histidine

arginine

histidine

Inorganic fluoride inhibits enolase. In an anaerobic system that is metabolizing glucose as a substrate, which compound would you expect to increase in concentration following the addition of fluoride?

2-phosphoglycerate

glucose

glyoxylate

phosphoenolpyruvate

pyruvate

2-phosphoglycerate

Glycogen is converted to monosaccharide units by:

glucokinase.

glucose-6-phosphatase

glycogen phosphorylase.

glycogen synthase.

glycogenase.

glycogen phosphorylase.

Galactosemia is a genetic error of metabolism associated with:

deficiency of galactokinase.

deficiency of UDP-glucose.

deficiency of UDP-glucose: galactose 1-phosphate uridylyltransferase.

excessive ingestion of galactose.

inability to digest lactose.

deficiency of UDP-glucose: galactose 1-phosphate uridylyltransferase.

During strenuous exercise, the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction in skeletal muscle must be reoxidized to NAD+ if glycolysis is to continue. The most important reaction involved in the reoxidation of NADH is:

dihydroxyacetone phosphate → glycerol 3-phosphate.

glucose 6-phosphate → fructose 6-phosphate.

isocitrate → α-ketoglutarate.

oxaloacetate → malate.

pyruvate → lactate.

pyruvate → lactate.

In an anaerobic muscle preparation, lactate formed from glucose labeled in C-3 and C-4 would be labeled in:

all three carbon atoms.

only the carbon atom carrying the OH.

only the carboxyl carbon atom.

only the methyl carbon atom.

the methyl and carboxyl carbon atoms.

only the carboxyl carbon atom.