BioChem Exam 4 (iClicker and exams)

Which one of the following enzymes and intermediates is not a part of the energy investment stage of glycolysis:

aldolase

DHAP (dihydroxy acetone phosphate)

PFK-1 (phosphofructokinase-1)

GAPDH (glyceraldehyde-3-phosphate dehydrogenase)

Fructose-6-phosphate (F6P)

Phosphohexose isomerase

GAPDH (glyceraldehyde-3-phosphate dehydrogenase)

Which one of the following enzymes and intermediates is not a part of the energy generation stage of glycolysis:

GAPDH (glyceraldehyde-3-phosphate dehydrogenase)

hexokinase

Pyruvate kinase

1,3-BPG (1,3-bisphosphoglycerate)

3-phosphoglycerate

Pyruvate

hexokinase

What is the correct stoichiometry of products of the energy investment stage of glycolysis (assume 1mol of glucose is being used):

2mol ATP, 0mol NADH, 2mol glyceraldehyde-3-phosphate, 0mol pyruvate.

-2mol ATP, 0mol NADH, 2mol glyceraldehyde-3-phosphate, 0mol pyruvate.

-2mol ATP, 0mol NADH, 1mol glyceraldehyde-3-phosphate, 0mol pyruvate.

4mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

2mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

4mol ATP, 2mol NADH, 2mol glyceraldehyde-3-phosphate, 2mol pyruvate.

2mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

What is the correct stoichiometry of products of the energy generation stage of glycolysis (assume 1mol of glucose is being used):

2mol ATP, 0mol NADH, 2mol glyceraldehyde-3-phosphate, 0mol pyruvate.

-2mol ATP, 0mol NADH, 2mol glyceraldehyde-3-phosphate, 0mol pyruvate.

-2mol ATP, 0mol NADH, 1mol glyceraldehyde-3-phosphate, 0mol pyruvate.

4mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

2mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

4mol ATP, 2mol NADH, 2mol glyceraldehyde-3-phosphate, 2mol pyruvate.

4mol ATP, 2mol NADH, 0mol glyceraldehyde-3-phosphate, 2mol pyruvate.

Which of the following enzymes produce ATP and are irreversible:

Pyruvate kinase

Hexokinase

PFK-1 (phosphofructokinase-1)

Phosphoglycerate kinase

Both A) and D)

Pyruvate kinase

Nutrient "X" can be catabolized within the cell. Which of the following is true?

• Nutrient "X" will undergo oxidation.

• Break down of Nutrient "X" could lead to the production of an electrochemical gradient.

• Nutrient "X" has a higher free energy value than carbon dioxide and water.

• Nutrient "X" may be broken down to molecules that can be used in substrate-level phosphorylation.

  • All of the above.

• All of the above.

Nucleophilic substitution and redox reactions are two very important classes of reactions within energy metabolism.  Which of the following are true about these reactions?

• Phosphoryl functional groups are poor leaving groups for nucleophilic substitution.

• Redox reactions can only occur between metal ions.

• ATP hydrolysis is a redox reaction.

• Free energy from ATP hydrolysis can be conserved in the covalent attachment of a phosphoryl group to another compound.

• A reduced molecule with a high reduction potential will transfer electrons to an oxidized molecule with low reduction potential and perform work in the process.

• Free energy from ATP hydrolysis can be conserved in the covalent attachment of a phosphoryl group to another compound.

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

αKGA+CO2+2H++2e−→IsocitrateE′∘=−0.380VαKGA+CO2+2H++2e−→IsocitrateE′∘=−0.380V

NAD++H++2e−→NADHE′∘=−0.320VNAD++H++2e−→NADHE′∘=−0.320V

Which of the following is true if the full reaction is:

Isocitrate+NAD+→αKGA+CO2+NADH+H+

• Isocitrate has a greater affinity for electrons than does NAD+.

• α-KGA is reduced compared to isocitrate.

• NAD+ is the electron acceptor, Isocitrate is the electron donor, and the reaction as written above is spontaneous at standard conditions. (correct)

• NADH is the oxidized form of NAD+.

• All of the above are true.

• NAD+ is the electron acceptor, Isocitrate is the electron donor, and the reaction as written above is spontaneous at standard conditions. (correct)

A biological steady state:

• maintains reactions at chemical equilibrium within the cell.

• is maintained by adjustments in metabolic flux.

• is a reversible state of the system.

• allows turnover (utilization and reproduction) of biomolecules while maintaining a constant concentration of biomolecules.

• All of the above.

• A), B), and D).

• B) and D).

• B) and D).

Allosteric :

Regulation mechanism where in binding of a modulator to a protein results in a higher or lower activity of the protein.

Covalent modification :

Regulation mechanism where in attachment of an organic functional group results in a higher or lower activity of the protein.  

Protein turnover :

Regulation mechanism where in increased or decreased genetic expression of an enzyme leads to higher or lower flux through a pathway.

Sequestration :

Regulation mechanism where in an enzyme that catalyzes an irreversible step in a pathway is removed from the cellular compartment where the pathway normally runs.

Which of the following statements is not true concerning fermentation of glucose (converting it to lactate) in mammalian cells?

PFK-1 is one of the enzymes of the pathway.

It results in net synthesis of ATP.

It results in net synthesis of NADH.

It is one of only a few metabolic processes that can make ATP independent of oxygen.

It is an exergonic process.

It results in net synthesis of NADH.

The malate/aspartate shuttle:

if inhibited, could lead to the accumulation of cytosolic glyceraldehyde-3-phosphate within the cell (assume the glycerol-3-phosphate shuttle, LDH, and GNG are not found in this particular cell).

if inhibited, would have little to no effect on the flux of GNG (gluconeogenesis).

if inhibited, would result in the accumulation of cytosolic NAD+ (assume the glycerol-3-phosphate shuttle and GNG are not found in this particular cell).

D) if inhibited, would result in the accumulation of cytosolic lactate (assume the glycerol-3-phosphate shuttle and GNG are not found in this particular cell).

A) and D).

A), B), and D).

A), B), C), and D).

A) and D).

A liver cell is capable of running glycolysis and gluconeogenesis (GNG).  Based upon this which of the following statements are true?

PFK-1 will preferentially adopt the R-state when ATP levels are high and F26BP levels are low.

Active PFK-2 leads to decreased flux through glycolysis.

Increased levels of F26BP within a liver cell will lead to increased flux through glycolysis and a subsequent depression in blood glucose content.

Glycolysis and GNG can have similar flux within the liver cell as they are found in different compartments (organelles).

None of the above are correct.

Increased levels of F26BP within a liver cell will lead to increased flux through glycolysis and a subsequent depression in blood glucose content.

Lactate fermentation:

produces lactate that can be used to generate glucose in mammals.

is a means of producing NAD⁺ for gluconeogenesis (GNG) in skeletal muscle.

requires mitochondrial transporters for completion.

is only run in anaerobic conditions.

All of the above.

produces lactate that can be used to generate glucose in mammals.

NADH :

Required cytosolic substrate for GNG supplied by the cytosolic conversation of malate to oxaloacetate (OAA).

NAD+ :

Required cytosolic substrate for glycolysis supplied by the cytosolic conversation of oxaloacetate (OAA) to malate.

glyceraldehyde-3-phosphate :

3-carbon product of the energy investment stage.

Pyruvate :

3-carbon product of the energy generation phase.

Lactate :

3-carbon product of fermentation.

Energy conservation in thioesters, acetyl-CoA and succinyl-CoA:

ensure irreversibility of the citrate synthase reaction, in the case of acetyl-CoA.

ensure the production of GTP in the case of succinyl-CoA.

in the case of acetyl-CoA is required because OAA concentration in the cell are very low due to the endergonic nature of the malate dehydrogenase reaction.

occurs through large enzyme complexes.

All of the above responses are correct and therefore E is my best choice.

All of the above responses are correct and therefore E is my best choice.

The Pyruvate dehydrogenase complex (PDH-complex or PDC) is one of the largest enzyme complexes observed in biological systems.  Chapter 12 discusses its structure and function.  Given these topics which of the following is true?

The acetyl group is transferred from lipoate to CoA in the active site of E2.

FADH₂ is a final product of the enzyme.

The decarboxylation of pyruvate is accomplished by the lipoate coenzyme leading to its (lipoate) acetylation (addition of an acetyl group).

The mechanism of the enzyme is unique to the PDH complex and is not observed in any other enzyme known to mankind.

A) and C).

The acetyl group is transferred from lipoate to CoA in the active site of E2.

The citric acid cycle is a central metabolic pathway in mammalian organisms. Sources of acetyl-CoA for the pathway include:

Pyruvate derived from glucose.

Pyruvate derived from amino acids.

Pyruvate derived from fatty acids.

All of the above

A) and B)

A) and B)

The citric acid cycle is a central metabolic pathway in mammalian organisms. Which of the following statements is true of the interconnections it makes with other pathways?

Depletion of OAA, through processes like GNG, would result in reduced flux IF nothing resupplied OAA.

PDH complex (PDC) is the first step in this pathway.

The pathway does not require molecular oxygen and is therefore oxygen independent.

The pathway is strictly catabolic.

A), B), and C).

Depletion of OAA, through processes like GNG, would result in reduced flux IF nothing resupplied OAA.

The citric acid cycle is a central metabolic pathway in mammalian organisms. Which of the following statements are true regarding its products and its regulation?

The pathway leads to the net synthesis of OAA.

If the pathway is fed α-ketoglutarate (from the amino acid Glu) it will lead to the net synthesis of OAA.

Accumulation of NADH will result in decreased flux of this pathway.

It results in the production of 3 NADH, 1 FADH₂, 1 GTP, and 3 CO₂.

All of the above.

A), B), and C).

B) and C).

B) and C).