Metabolic Pathways: Glycolysis, Gluconeogenesis, and More

In comparison with the resting state, actively contracting human muscle tissue has a:

higher rate of lactate formation.

Which of the following is NOT a key enzyme for regulating glucose breakdown?

Phosphoglycerate kinase

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

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

Which statement about gluconeogenesis is FALSE?

It consists entirely of the reactions of glycolysis, operating in the reverse direction.

Why is an anaerobic fate of pyruvate necessary in skeletal muscle?

It allows for the re-oxidation of NADH to NAD*, as NAD is in limited supply during anaerobic conditions.

Which cofactor participates directly in most oxidation-reduction reactions in the fermentation of glucose to lactate?

NAD+/NADH.

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

NAD+.

In humans, the Cori cycle shifts part of the metabolic burden of active muscle to the liver. Which two metabolic pathways are involved in this cycle?

Glycolysis and gluconeogenesis.

Which statement is INCORRECT

Under anaerobic conditions pyruvate does not form because glycolysis does not occur.

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

2 mol of NADH and 2 mol of ATP.

The pentose phosphate pathway is multifunctional with metabolic flexibility. Which statement is false with respect to this pathway?

It generates NADH for reductive biosynthesis.

Glycogenin:

It is the primer on which new glycogen chains are initiated.

Which organ cannot use fatty acids as fuels for metabolic energy, and relies on a

steady glucose supply for fuel?

Brain.

The enzyme glycogen phosphorylase:

It catalyzes a cleavage of (α1 → 4) bonds.

Which statement is NOT associated with controlling glycogen synthesis in the liver?

Insulin activates glycogen synthase kinase 3.

Glycogen synthase and glycogen phosphorylase are both regulated by phosphorylation. Which answer choice most accurately describes the process.

Phosphorylation of glycogen phosphorylase increases the rate of glycogen breakdown while phosphorylation of glycogen synthase decreases the rate of glycogen synthesis.

When six molecules of ribulose 5-phosphate are converted to pyruvate, how many ATP and NADH are produced?

8 molecules of ATP and 5 molecules of NADH.

Which substrate cannot contribute to net gluconeogenesis in the mammalian liver?

Palmitate.

Glycogen converted to monosaccharide by:

glycogen phosphorylase.

After glycolysis, what catabolic pathways can pyruvate participate in?

I. It can be oxidized to acetyl-CoA and participate in the citric acid cycle when oxygen is available; II. In human muscle, it can be reduced to lactate without using oxygen; III. It can be reduced to ethanol by yeast without using oxygen.

The metabolic function of the pentose phosphate pathway is to:

generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids.

What is the purpose of phosphorylating glucose in cytosol?

trap glucose in the cell, destabilize it and facilitate the next series of metabolic steps

What is the metabolic function of the pentose phosphate pathway?

To generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids.

What is the purpose of phosphorylating glucose in the cytosol?

To trap glucose in the cell, destabilize it, and facilitate the next series of metabolic steps.

Which process does NOT occur in the steps of glycolysis between glyceraldehyde 3-phosphate and phosphoenolpyruvate?

A hydration reaction.

The anaerobic conversion of one molecule of glucose to two molecules of lactate

by fermentation is accompanied by a net gain of:

Two molecules of ATP.

In terms of the reaction mechanism, to which enzyme in glycolysis is phosphoglucomutase MOST similar?

Phosphoglycerate mutase.

Which statement regarding regulation of glycolysis and gluconeogenesis is FALSE?

Phosphofructokinase-1 and fructose 1,6-bisphosphatase are prevented from forming a futile cycle by reversible covalent modification.

What is true regarding glycogen granules in liver cells?

All of the statements are true.

Which enzyme does NOT play a role in glycogen metabolism?

Fructose 1,6-bisphosphatase.

What roles does ATP have with respect to PFK-1?

Substrate and allosteric inhibitor.

Which statement about the pentose phosphate pathway is NOT correct?

It requires the participation of molecular oxygen.

Which statement does NOT describe a general function of the pentose phosphate pathway?

The pentose phosphate pathway produces reduced molecules whose electrons may be shuttled to the mitochondria for oxidative phosphorylation.

The conversion of one molecule of fructose 1,6-bisphosphate to two molecules of pyruvate by the glycolytic pathway results in a net formation of_______molecule(s) of ______ and _______molecule(s) of ATP.

two; NADH; four

Which enzyme class does phosphoglycerate mutase belong to?

Isomerase.

How does glucokinase (hexokinase IV) differ from hexokinase (hexokinase I)?

It requires larger concentrations of glucose before reaching maximal activity.

What is the general name for an enzyme that catalyzes an intramolecular phosphoryl shift?

Mutase.

Which enzyme is used in both glycolysis and gluconeogenesis?

3-phosphoglycerate kinase.

What is the effect of insulin on glycogen phosphorylase in skeletal muscle?

It is inhibited.

Which substance activates glycogen synthase b in the liver?

Both insulin and glucose 6-phosphate.

Which statement about gluconeogenesis in animal cells is true?

The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by phosphofructokinase-1, the enzyme involved in glycolysis.

What reaction in glycolysis is a ketose to aldose isomerization?

Triose phosphate isomerase.

What reaction in glycolysis is an aldose to ketose isomerization?

Phosphohexose isomerase.

Which enzyme is used in both glycolysis and gluconeogenesis.

3-phosphoglycerate kinase

Which transcription factor regulates the transcription of glycolytic or gluconeogenic enzymes?

Carbohydrate response element binding protein.

What are the three enzymes in glycolysis that must be bypassed in gluconeogenesis?

Hexokinase, phosphofructokinase-1, and pyruvate kinase.

What does glycogen synthase do?

It catalyzes the addition of glucose residues to the nonreducing end of a glycogen chain by formation of (α1 → 4) bonds.

Which products of glycolysis are considered energy storage molecules?

ATP and NADH.

In humans, gluconeogenesis:

can result in the conversion of protein into blood glucose.

What is NOT true about glycolysis in anaerobic muscle?

It is an endergonic process.

How does glycogen phosphorylase respond to glucagon in liver tissue?

It is activated.

In glycogen ______ glycosidic bonds occur at branch points, while all

others are___ glycosidic bonds

(α1 → 6): (α1 → 4)

Which enzyme phosphorylates glycogen synthase a to convert it to glycogen synthase b?

Glycogen synthase kinase 3.

In some tissues, an increase in insulin will substantially increase the glucose transporters in the cell membrane and the transport of glucose into cells. Which tissues react in this manner?

Muscle and adipose tissue.

Which statement about the pentose phosphate pathway is correct?

It provides precursors for the synthesis of nucleotides.

What type of metabolic process is glycolysis an example of?

Fermentation.

What type of reaction generates a high-energy molecule in glycolysis?

A dehydration reaction.

In a tissue that metabolizes glucose via the pentose phosphate pathway, where does C-1 of glucose principally end up?

In carbon dioxide.

What method directly regulates PFK-1?

Allosteric activation by AMP.

Which compounds are considered high-energy intermediates in glycolysis?

1,3-bisphosphoglycerate and phosphoenolpyruvate.

Which compound cannot serve as the starting material for gluconeogenesis?

Acetate.

Glycogen phosphorylase a can be inhibited at an allosteric site by:

Glucose.

What is the process of breaking down glycogen to glucose 1-phosphate called?

Glycogenolysis.

The oxidation of three molecules of glucose by the pentose phosphate pathway may result in the production of _______molecules of pentose, ________molecules of NADPH, and ______molecules of CO2.

Three, six, three

Which products are generated by the pentose phosphate pathway?

NADPH and Ribose 5-phosphate.

In the alcoholic fermentation of glucose by yeast, thiamine pyrophosphate is a coenzyme required by:

pyruvate decarboxylase

Which reaction in glycolysis produces ATP as a product?

pyruvate kinase.

Which reaction in glycolysis requires ATP as a substrate?

hexokinase.

What is the ultimate electron acceptor in the fermentation of glucose to ethanol?

Acetaldehyde.

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:

Pyruvate → lactate.

When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts anaerobically because:

Under aerobic conditions, most of the pyruvate generated from glycolysis is oxidized by the citric acid cycle rather than reduced to lactate.

What is the net yield of ATP produced by the anaerobic fermentation of one molecule of sucrose in myocytes?

Four ATP.

What is the net yield of ATP produced by the anaerobic fermentation of one molecule of galactose to two molecules of lactate in myocytes?

Two ATP.

Two reactions, extra to the ten reactions of glycolysis, are involved in ethanol fermentation by yeast under anaerobic conditions. What is the purpose served by these two reactions in the metabolism of yeast cells?

They are required to both re-oxidize limited amounts of NADH and sustain glycolysis, ensuring ATP production.

Ethanol is produced by yeast under anaerobic conditions. This is accomplished by 2 reactions beyond the 10 reactions of glycolysis. What is the purpose served by these 2 reactions in the metabolism of yeast cells?

They are required to reoxidize NADH.

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 shown

(R = 8.315 J/mol • K and T = 298 K)?

🔺G'° is +1.7 kJ/mol.

After a meal rich in carbohydrates, which change would NOT be expected in a normal human?

Increased activity of glucose 6-phosphatase in hepatocytes.

What concentration of ATP inhibits cellular isozymes of pyruvate kinase?

High concentrations of ATP.

What is substrate-level phosphorylation?

ATP synthesis when the phosphate donor is a substrate with a high phosphoryl-transfer potential.

Animals store a great deal more energy in fats than in glycogen. Fats also store more energy per gram than glycogen. Which is a reason for having some energy stored in glycogen, rather than using fats alone?

Glucose can be released very quickly from glycogen to provide energy.