Question 1

When glucagon binds to receptors on mammalian liver cells,which of the following occurs due to enzyme phosphorylation?

Accepted Answer

When glucagon binds to receptors on mammalian liver cells, it leads to a cascade of events that ultimately activates FBPase-2 (fructose-2,6-bisphosphatase 2), which in turn promotes gluconeogenesis, the process of generating glucose from non-carbohydrate sources. This is in contrast to glycolysis, which is the breakdown of glucose to pyruvate for energy production. Glucagon generally signals the liver to release glucose into the blood, thus activating pathways that increase glucose levels, such as gluconeogenesis.

Question 2

What sequence of enzymes allows for the synthesis of glycogen from glucose-6-phosphate?

Accepted Answer

The correct sequence for the synthesis of glycogen from glucose-6-phosphate involves first converting glucose-6-phosphate to glucose-1-phosphate via phosphoglucomutase. Then, UDP-glucose pyrophosphorylase converts glucose-1-phosphate to UDP-glucose, which is a direct substrate for glycogen synthase, the enzyme that adds glucose units to the growing glycogen chain. Finally, amylo-(1,4 to 1,6)-transglycosylase (also known as the branching enzyme) introduces 1,6-branches into the glycogen molecule, enhancing its solubility and accessibility to enzymes.

Question 3

Which of the following activators is correctly paired with the glycolytic or gluconeogenic enzyme that it activates?

Accepted Answer

Fructose-2,6-bisphosphate activates phosphofructokinase, which is a glycolytic enzyme. The other choices are incorrect: glucose-6-phosphate activates hexokinase, which is correct for glycolysis but not gluconeogenesis; AMP activates AMP-activated protein kinase (AMPK), which inhibits glycolysis and activates gluconeogenesis but not a specific enzyme; ATP activates pyruvate carboxylase, which is a gluconeogenic enzyme but not a glycolytic enzyme; citrate activates citrate lyase, which is involved in fatty acid synthesis but not glycolysis or gluconeogenesis.

Question 4

The oxidative phase of the pentose phosphate pathway has _____ oxidation reactions,effectively oxidizing an ___________ to ____________.

Accepted Answer

The answer of The oxidative phase of the pentose phosphate...

Question 5

In the vertebrate liver,which major regulatory point is bypassed during fructose metabolism,often leading to conversion of excess fructose into fat?

Accepted Answer

Phosphofructokinase is a major regulatory point in glycolysis, controlling the rate-limiting step in the pathway. However, during fructose metabolism, fructose is converted to fructose-1-phosphate by fructokinase, which bypasses this regulatory step. This often leads to an overproduction of acetyl-CoA, which can be used for lipogenesis, resulting in the conversion of excess fructose into fat.

Question 6

Which of the following intermediates is a feed-forward activator of pyruvate kinase?

Accepted Answer

Fructose-1,6-bisphosphate is a feed-forward activator of pyruvate kinase, enhancing the enzyme's activity as part of the glycolytic pathway. This mechanism helps regulate the rate of glycolysis, ensuring efficient energy production.

Question 7

Which of the following is correctly paired with the glycolytic intermediate that serves as its precursor?

Accepted Answer

The answer of Which of the following is correctly paired...

Question 8

Fill in the missing two intermediates of glycolysis:

Accepted Answer

The answer of Fill in the missing two intermediates of...

Question 9

Which of the following enzymes is activated when acted on by phosphoprotein phosphatase 1?

Accepted Answer

Phosphoprotein phosphatase 1 is known to activate glycogen synthase by removing the phosphate group from it, promoting glycogen synthesis.

Question 10

A transketolase enzyme transfers a _____ carbon fragment from a(n)________ to a(n)________.

Accepted Answer

Transketolase enzyme transfers a 2-carbon fragment from a ketose to an aldose. This is known as a transketolase reaction in the pentose phosphate pathway. Option A is incorrect as it states the transfer of a 2-carbon fragment from an aldose to a ketose. Option C is incorrect as it states the transfer of a 2-carbon fragment from a ketose to a ketose. Option D is incorrect as it states the transfer of a 3-carbon fragment from an aldose to a ketose. Option E is incorrect as it states the transfer of a 3-carbon fragment from a ketose to an aldose.

Question 11

When lipid biosynthesis is active using carbohydrates as a source of carbon,three things are needed: NADPH,ATP and acetyl-CoA (from pyruvate).Which of the following best explains the operation of the pentose phosphate pathway (PPP)under such conditions? G6P = glucose-6-phosphate,F6P = fructose-6-phosphate,G3P = glyceraldehyde-3-phosphate

Accepted Answer

The PPP generates NADPH, which is needed for lipid biosynthesis, and it also produces ribose-5-phosphate (R5P), which is used in nucleotide biosynthesis. In order to generate NADPH and R5P, the PPP oxidizes glucose-6-phosphate (G6P) to ribulose-5-phosphate (Ru5P), generating two molecules of NADPH for every molecule of G6P that is oxidized. This process also generates fructose-6-phosphate (F6P), which can be recycled back to G6P to enter the PPP again. One molecule of glyceraldehyde-3-phosphate (G3P) is also produced for every three molecules of G6P that enter the PPP. This G3P can be converted to pyruvate and used to generate ATP and acetyl-CoA through glycolysis. Therefore, option D is the best choice as it describes both the production of NADPH and recycling of F6P back to G6P, while also allowing for the production of ATP and acetyl-CoA through glycolysis as needed.

Question 12

In the mammalian liver,hexokinase IV is sequestered in _______ when glucose concentrations are low.When glucose concentrations are high,it is found in the cytosol bound to the enzyme ________.

Accepted Answer

The answer of In the mammalian liver,hexokinase IV is sequestered...

Question 13

When glucagon binds to its receptor on a liver cell,which of the following sequence of events occurs to activate protein kinase A?

Accepted Answer

Glucagon binding to its receptor results in activation of G protein, which then activates adenylate cyclase. Adenylate cyclase produces cAMP, which activates protein kinase A. Therefore, the correct sequence of events is activation of G protein, activation of adenylate cyclase, and production of cAMP. Choice B correctly matches this sequence.

Question 14

Provide the missing names or structures for the following scheme of the fermentation of pyruvate

Accepted Answer

The answer of Provide the missing names or structures for...

Question 15

The conversion of ribulose-5-phosphate to xylulose-5-phosphate requires what enzyme?

Accepted Answer

The conversion of ribulose-5-phosphate to xylulose-5-phosphate is a result of an epimerization reaction, which involves the interconversion of stereochemistries of two adjacent carbons. The enzyme responsible for this reaction is phosphopentose epimerase. Therefore, choice B is the correct answer.

Question 16

Experiments that investigated the Pasteur effect showed that when oxygen is introduced to cells where glycolysis is occurring,all intermediates beginning with ________ become depleted due to inhibition of the enzyme _________.

Accepted Answer

The Pasteur effect refers to the phenomenon where the rate of glycolysis decreases when oxygen is introduced to cells. This is because aerobic respiration, which occurs in the presence of oxygen, is more efficient at producing ATP than anaerobic glycolysis alone. The depletion of intermediates beginning with fructose-1,6-bisphosphate indicates that the enzyme phosphofructokinase, which catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, is inhibited when oxygen is present. This inhibition is a result of the cell's shift towards aerobic respiration.

Question 17

If a residue of glucose in glycogen is removed from the glycogen molecule and then allowed to proceed through glycolysis to pyruvate,what is the net production of ATP?

Accepted Answer

The answer of If a residue of glucose in glycogen...

Question 18

In its non-phosphorylated state,glycogen phosphorylase can be activated by which of the following molecules?

Accepted Answer

Glycogen phosphorylase can be activated by AMP in its non-phosphorylated state. This is known as the AMP-activated protein kinase (AMPK) pathway, which is activated during times of low energy availability and signals for the breakdown of glycogen to increase ATP production. The other molecules listed do not activate glycogen phosphorylase in its non-phosphorylated state.

Question 19

Besides its role in glycogen synthesis,which of the following directly relies on UDP-glucose?

Accepted Answer

The answer of Besides its role in glycogen synthesis,which of...

Question 20

For the interconversion of an aldose and ketose,show the intermediate of the reaction.

Accepted Answer

The answer of For the interconversion of an aldose and...

Quiz 13: Carbohydrate Metabolism: Glycolysis, gluconeogenesis, glycogen Metabolism, and the Pentose Phosphate Pathway

When glucagon binds to receptors on mammalian liver cells,which of the following occurs due to enzyme phosphorylation?

What sequence of enzymes allows for the synthesis of glycogen from glucose-6-phosphate?

Which of the following activators is correctly paired with the glycolytic or gluconeogenic enzyme that it activates?

The oxidative phase of the pentose phosphate pathway has _ oxidation reactions,effectively oxidizing an _ to ______.

In the vertebrate liver,which major regulatory point is bypassed during fructose metabolism,often leading to conversion of excess fructose into fat?

Which of the following intermediates is a feed-forward activator of pyruvate kinase?

Which of the following is correctly paired with the glycolytic intermediate that serves as its precursor?

Fill in the missing two intermediates of glycolysis:

Which of the following enzymes is activated when acted on by phosphoprotein phosphatase 1?

A transketolase enzyme transfers a _ carbon fragment from a(n) to a(n) ____.

In the mammalian liver,hexokinase IV is sequestered in _ when glucose concentrations are low.When glucose concentrations are high,it is found in the cytosol bound to the enzyme __.

When glucagon binds to its receptor on a liver cell,which of the following sequence of events occurs to activate protein kinase A?

Provide the missing names or structures for the following scheme of the fermentation of pyruvate

The conversion of ribulose-5-phosphate to xylulose-5-phosphate requires what enzyme?

Experiments that investigated the Pasteur effect showed that when oxygen is introduced to cells where glycolysis is occurring,all intermediates beginning with become depleted due to inhibition of the enzyme _.

If a residue of glucose in glycogen is removed from the glycogen molecule and then allowed to proceed through glycolysis to pyruvate,what is the net production of ATP?

In its non-phosphorylated state,glycogen phosphorylase can be activated by which of the following molecules?

Besides its role in glycogen synthesis,which of the following directly relies on UDP-glucose?

For the interconversion of an aldose and ketose,show the intermediate of the reaction.

Quiz 13: Carbohydrate Metabolism: Glycolysis, gluconeogenesis, glycogen Metabolism, and the Pentose Phosphate Pathway

When glucagon binds to receptors on mammalian liver cells,which of the following occurs due to enzyme phosphorylation?

What sequence of enzymes allows for the synthesis of glycogen from glucose-6-phosphate?

Which of the following activators is correctly paired with the glycolytic or gluconeogenic enzyme that it activates?

The oxidative phase of the pentose phosphate pathway has _____ oxidation reactions,effectively oxidizing an ___________ to ____________.

In the vertebrate liver,which major regulatory point is bypassed during fructose metabolism,often leading to conversion of excess fructose into fat?

Which of the following intermediates is a feed-forward activator of pyruvate kinase?

Which of the following is correctly paired with the glycolytic intermediate that serves as its precursor?

Fill in the missing two intermediates of glycolysis:

Which of the following enzymes is activated when acted on by phosphoprotein phosphatase 1?

A transketolase enzyme transfers a _____ carbon fragment from a(n) ________ to a(n) ________.

In the mammalian liver,hexokinase IV is sequestered in _______ when glucose concentrations are low.When glucose concentrations are high,it is found in the cytosol bound to the enzyme ________.

When glucagon binds to its receptor on a liver cell,which of the following sequence of events occurs to activate protein kinase A?

Provide the missing names or structures for the following scheme of the fermentation of pyruvate

The conversion of ribulose-5-phosphate to xylulose-5-phosphate requires what enzyme?

Experiments that investigated the Pasteur effect showed that when oxygen is introduced to cells where glycolysis is occurring,all intermediates beginning with ________ become depleted due to inhibition of the enzyme _________.

If a residue of glucose in glycogen is removed from the glycogen molecule and then allowed to proceed through glycolysis to pyruvate,what is the net production of ATP?

In its non-phosphorylated state,glycogen phosphorylase can be activated by which of the following molecules?

Besides its role in glycogen synthesis,which of the following directly relies on UDP-glucose?

For the interconversion of an aldose and ketose,show the intermediate of the reaction.

The oxidative phase of the pentose phosphate pathway has _ oxidation reactions,effectively oxidizing an _ to ______.

A transketolase enzyme transfers a _ carbon fragment from a(n) to a(n) ____.

In the mammalian liver,hexokinase IV is sequestered in _ when glucose concentrations are low.When glucose concentrations are high,it is found in the cytosol bound to the enzyme __.

Experiments that investigated the Pasteur effect showed that when oxygen is introduced to cells where glycolysis is occurring,all intermediates beginning with become depleted due to inhibition of the enzyme _.