Question 1

Which of the following pairs of phosphorylated molecules contains an intermediate of glycolysis with high phosphate transfer potential and one with low phosphate transfer potential?

Accepted Answer

Phosphoenolpyruvate (PEP) has a high phosphate transfer potential, making it a powerful molecule for transferring phosphate groups to ADP to form ATP. Glyceraldehyde-3-phosphate, on the other hand, has a lower phosphate transfer potential and is an earlier intermediate in the glycolysis pathway.

Question 2

Conversion of pyruvate to acetaldehyde requires _______ while conversion of acetaldehyde to ethanol requires _______.

Accepted Answer

The conversion of pyruvate to acetaldehyde in the first step of alcoholic fermentation requires thiamine pyrophosphate as a coenzyme. The conversion of acetaldehyde to ethanol in the second step requires NADH as a coenzyme. Therefore, the correct choice is E, which includes thiamine pyrophosphate and NADH. The other choices are incorrect as they either do not include the required coenzymes or include coenzymes that are not involved in the reactions.

Question 3

Besides two molecules of pyruvate, what are the net products of glycolysis?

Accepted Answer

The net products of glycolysis are 2 molecules of ATP and 2 molecules of NADH. While 4 ATP molecules are produced in total during glycolysis, 2 of them are used during the preparatory phase of the pathway, resulting in a net yield of 2 ATP molecules. Similarly, 2 molecules of NAD+ are reduced to NADH during the energy-yielding phase of glycolysis, resulting in a net yield of 2 NADH molecules.

Question 4

During aerobic glycolysis, pyruvate is most likely oxidized to ________ while in anaerobic glycolysis, pyruvate is converted to _________.

Accepted Answer

During aerobic glycolysis, pyruvate is oxidized to acetyl CoA, which then enters the citric acid cycle. In anaerobic glycolysis, pyruvate is converted to lactate in a process known as lactic acid fermentation.

Question 5

Which of the following glycolytic reactions is freely reversible?

Accepted Answer

Triose phosphate isomerase catalyzes the conversion of dihydroxyacetone phosphate (DHAP) to glyceraldehyde 3-phosphate (G3P) which is freely reversible. The other three reactions mentioned in the options are irreversible and highly regulated steps in the glycolytic pathway.

Question 6

The conversion of 3-phosphoglycerate to phosphoenolpyruvate requires two reactions. Which of the following correctly identifies the types of reactions in the proper order of glycolysis?

Accepted Answer

The conversion of 3-phosphoglycerate to phosphoenolpyruvate involves an isomerization reaction catalyzed by the enzyme enolase, followed by a dehydration reaction catalyzed by the enzyme pyruvate kinase. Therefore, the correct order of reactions is isomerization followed by dehydration, which is represented by option D. The other options do not represent the correct order of reactions in glycolysis.

Question 7

Assuming that gluconeogenesis was active in a mammalian liver, under what conditions would PEPCK have more activity in the mitochondria than in the cytosol?

Accepted Answer

When lactate is the primary carbon source, pyruvate is converted to oxaloacetate in the mitochondria, and PEPCK activity is needed there to convert oxaloacetate to PEP, which can then be transported to the cytosol for gluconeogenesis.

Question 8

Which of the following enzymes is used by the gluconeogenic pathway but not the glycolytic pathway?

Accepted Answer

Phosphoenolpyruvate carboxykinase is an enzyme used by the gluconeogenic pathway but not the glycolytic pathway. Pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase, triose phosphate isomerase, and hexokinase are enzymes used by both pathways.

Question 9

In most bacteria that utilize glucose, what molecule both aids in transport of glucose into the cell and is phosphorylating agent for conversion of glucose to glucose-6-phosphate?

Accepted Answer

Phosphoenolpyruvate (PEP) is used in the phosphotransferase system (PTS) in bacteria to transport glucose into the cell and simultaneously phosphorylate it to glucose-6-phosphate.

Question 10

What is the initial step in the mechanism of fructose-1,6-bisphosphate aldolase when the substrate is fructose-1,6-bisphosphate in its open-chain form?

Accepted Answer

The initial step in the mechanism of fructose-1,6-bisphosphate aldolase involves the attack of the C-2 carbonyl group by the amine of lysine. This forms a Schiff base intermediate, facilitating the subsequent steps in the cleavage of fructose-1,6-bisphosphate into two three-carbon molecules.

Question 11

The conversion of phosphoenolpyruvate and ADP to pyruvate and ATP occurs in two distinct steps, first the transfer of the phosphate from PEP to ADP, then the conversion of enolpyruvate to pyruvate. Which of the following describes the reversibility of this process?

Accepted Answer

The conversion of phosphoenolpyruvate (PEP) to pyruvate involves the enzyme pyruvate kinase, where the first step (transfer of phosphate from PEP to ADP) is considered reversible under certain conditions, but the second step (conversion of enolpyruvate to pyruvate) is generally regarded as irreversible in physiological conditions.

Question 12

During the oxidation of glyceraldehyde-3-phosphate, what intermediate in the enzyme-catalyzed mechanism actually undergoes oxidation?

Accepted Answer

In the enzyme-catalyzed mechanism of glyceraldehyde-3-phosphate dehydrogenase, the thiohemiacetal intermediate is formed when the aldehyde group of glyceraldehyde-3-phosphate reacts with a cysteine residue in the enzyme. This thiohemiacetal is then oxidized to form a thioester intermediate.

Question 13

During the energy investment phase of glycolysis, _____ reaction(s)use ATP as a substrate while during the energy generation phase, _____ reactions produce ATP as a product.

Accepted Answer

During the energy investment phase of glycolysis, 2 reactions use ATP as a substrate (hexokinase and phosphofructokinase reactions), and during the energy generation phase, 2 reactions produce ATP as a product (phosphoglycerate kinase and pyruvate kinase reactions).

Question 14

Under conditions of strenuous exercise, gluconeogenesis occurs primarily in the _______ using _______ formed in the skeletal muscle

Accepted Answer

Gluconeogenesis during strenuous exercise occurs primarily in the liver, and lactate formed in the skeletal muscle is used as a substrate for this process.

Question 15

The reaction catalyzed by triose phosphate isomerase is most similar in mechanism to which of the following glycolytic enzymes?

Accepted Answer

Both triose phosphate isomerase and glucose-6-phosphate isomerase catalyze isomerization reactions, which involve the conversion of one isomer to another without a change in the number of carbon atoms. In particular, triose phosphate isomerase catalyzes the conversion of glyceraldehyde-3-phosphate to dihydroxyacetone phosphate, while glucose-6-phosphate isomerase catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate. The other enzymes listed (fructose-1,6-bisphosphate aldolase, phosphoglycerate mutase, enolase, and pyruvate kinase) catalyze more complex reactions involving bond cleavage or formation.

Question 16

With respect to carbons 1 and 2 of the intermediate in the conversion of glucose-6-phosphate to fructose-6-phosphate, which of the following would best describe this intermediate?

Accepted Answer

The intermediate in the conversion of glucose-6-phosphate to fructose-6-phosphate is an enediol, which is a molecule containing two hydroxyl groups (-OH) on adjacent carbons with a double bond between them (C=C-OH). This intermediate is formed when a phosphate group is removed from carbon 1 and a hydrogen atom is removed from carbon 2 of glucose-6-phosphate, resulting in a double bond between the two carbons and the formation of two hydroxyl groups on adjacent carbons. This enediol then quickly tautomerizes (shifts its double bond and proton) to form fructose-6-phosphate, which is a ketone with a single hydroxyl group on carbon 6.

Question 17

Which of the following is the fate of pyruvate in a blood cell?

Accepted Answer

Pyruvate is converted to lactate in blood cells through lactic acid fermentation. This process is used when oxygen is limited, such as during intense exercise, and allows for the production of ATP without the use of the electron transport chain. Acetyl CoA is the fate of pyruvate in aerobic respiration, carbon dioxide is a byproduct of aerobic respiration, and ethanol is produced in some organisms during fermentation, but not in human blood cells. Therefore, the correct answer is C, lactate.

Question 18

Which enzyme catalyzes the primary regulation site of glycolysis?

Accepted Answer

Phosphofructokinase-1 (PFK-1) catalyzes the third step in glycolysis, converting fructose-6-phosphate to fructose-1,6-bisphosphate. PFK-1 is the primary regulatory site of glycolysis, as it is inhibited by ATP and citrate and stimulated by ADP and AMP. The regulation of PFK-1 allows cells to balance their energy needs with their energy availability.

Question 19

If unregulated, which of the following pairs of enzymes would represent a futile cycle?

Accepted Answer

Fructose-1,6-bisphosphatase and phosphofructokinase catalyze opposing reactions in glycolysis and gluconeogenesis, respectively. If both were unregulated and active simultaneously, they would constitute a futile cycle, continuously converting fructose-6-phosphate to fructose-1,6-bisphosphate and back again, wasting energy.

Question 20

Which isoform of hexokinase is found in the vertebrate liver?

Accepted Answer

Hexokinase IV, also known as glucokinase, is the isoform found in the liver of vertebrates. It plays a key role in the regulation of blood glucose levels.

Quiz 13: Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Which of the following pairs of phosphorylated molecules contains an intermediate of glycolysis with high phosphate transfer potential and one with low phosphate transfer potential?

Conversion of pyruvate to acetaldehyde requires _ while conversion of acetaldehyde to ethanol requires _.

Besides two molecules of pyruvate, what are the net products of glycolysis?

During aerobic glycolysis, pyruvate is most likely oxidized to while in anaerobic glycolysis, pyruvate is converted to _.

Which of the following glycolytic reactions is freely reversible?

The conversion of 3-phosphoglycerate to phosphoenolpyruvate requires two reactions. Which of the following correctly identifies the types of reactions in the proper order of glycolysis?

Assuming that gluconeogenesis was active in a mammalian liver, under what conditions would PEPCK have more activity in the mitochondria than in the cytosol?

Which of the following enzymes is used by the gluconeogenic pathway but not the glycolytic pathway?

In most bacteria that utilize glucose, what molecule both aids in transport of glucose into the cell and is phosphorylating agent for conversion of glucose to glucose-6-phosphate?

What is the initial step in the mechanism of fructose-1,6-bisphosphate aldolase when the substrate is fructose-1,6-bisphosphate in its open-chain form?

The conversion of phosphoenolpyruvate and ADP to pyruvate and ATP occurs in two distinct steps, first the transfer of the phosphate from PEP to ADP, then the conversion of enolpyruvate to pyruvate. Which of the following describes the reversibility of this process?

During the oxidation of glyceraldehyde-3-phosphate, what intermediate in the enzyme-catalyzed mechanism actually undergoes oxidation?

During the energy investment phase of glycolysis, _ reaction(s) use ATP as a substrate while during the energy generation phase, _ reactions produce ATP as a product.

Under conditions of strenuous exercise, gluconeogenesis occurs primarily in the _ using _ formed in the skeletal muscle

The reaction catalyzed by triose phosphate isomerase is most similar in mechanism to which of the following glycolytic enzymes?

With respect to carbons 1 and 2 of the intermediate in the conversion of glucose-6-phosphate to fructose-6-phosphate, which of the following would best describe this intermediate?

Which of the following is the fate of pyruvate in a blood cell?

Which enzyme catalyzes the primary regulation site of glycolysis?

If unregulated, which of the following pairs of enzymes would represent a futile cycle?

Which isoform of hexokinase is found in the vertebrate liver?

Quiz 13: Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Which of the following pairs of phosphorylated molecules contains an intermediate of glycolysis with high phosphate transfer potential and one with low phosphate transfer potential?

Conversion of pyruvate to acetaldehyde requires _______ while conversion of acetaldehyde to ethanol requires _______.

Besides two molecules of pyruvate, what are the net products of glycolysis?

During aerobic glycolysis, pyruvate is most likely oxidized to ________ while in anaerobic glycolysis, pyruvate is converted to _________.

Which of the following glycolytic reactions is freely reversible?

The conversion of 3-phosphoglycerate to phosphoenolpyruvate requires two reactions. Which of the following correctly identifies the types of reactions in the proper order of glycolysis?

Assuming that gluconeogenesis was active in a mammalian liver, under what conditions would PEPCK have more activity in the mitochondria than in the cytosol?

Which of the following enzymes is used by the gluconeogenic pathway but not the glycolytic pathway?

In most bacteria that utilize glucose, what molecule both aids in transport of glucose into the cell and is phosphorylating agent for conversion of glucose to glucose-6-phosphate?

What is the initial step in the mechanism of fructose-1,6-bisphosphate aldolase when the substrate is fructose-1,6-bisphosphate in its open-chain form?

The conversion of phosphoenolpyruvate and ADP to pyruvate and ATP occurs in two distinct steps, first the transfer of the phosphate from PEP to ADP, then the conversion of enolpyruvate to pyruvate. Which of the following describes the reversibility of this process?

During the oxidation of glyceraldehyde-3-phosphate, what intermediate in the enzyme-catalyzed mechanism actually undergoes oxidation?

During the energy investment phase of glycolysis, _____ reaction(s) use ATP as a substrate while during the energy generation phase, _____ reactions produce ATP as a product.

Under conditions of strenuous exercise, gluconeogenesis occurs primarily in the _______ using _______ formed in the skeletal muscle

The reaction catalyzed by triose phosphate isomerase is most similar in mechanism to which of the following glycolytic enzymes?

With respect to carbons 1 and 2 of the intermediate in the conversion of glucose-6-phosphate to fructose-6-phosphate, which of the following would best describe this intermediate?

Which of the following is the fate of pyruvate in a blood cell?

Which enzyme catalyzes the primary regulation site of glycolysis?

If unregulated, which of the following pairs of enzymes would represent a futile cycle?

Which isoform of hexokinase is found in the vertebrate liver?

Conversion of pyruvate to acetaldehyde requires _ while conversion of acetaldehyde to ethanol requires _.

During aerobic glycolysis, pyruvate is most likely oxidized to while in anaerobic glycolysis, pyruvate is converted to _.

During the energy investment phase of glycolysis, _ reaction(s) use ATP as a substrate while during the energy generation phase, _ reactions produce ATP as a product.

Under conditions of strenuous exercise, gluconeogenesis occurs primarily in the _ using _ formed in the skeletal muscle