Biochemistry : Glycolysis Carbohydrate Intermediates

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Glycolysis Carbohydrate Intermediates

In muscle, glucose-6-phosphate is a common intermediate among __________.

Possible Answers:

glycolysis and glycogenesis

pentose phosphate pathways, glycogenin synthesis, and glycolysis

pentose phosphate pathway, glycogenesis, and glycolysis

pentose phosphate pathway, glycogenesis, and gluconeogenesis

glycogenesis, Krebs cycle, and glycolysis 

Correct answer:

pentose phosphate pathway, glycogenesis, and glycolysis

Explanation:

Glucose-6-phosphate (G6P) is the first molecule of the pentose phosphate pathway where it is acted upon by glucose-6-phosphate dehydrogenase. G6P is the result of the hexokinase (first) reaction in glycolysis. What is key here is that the tissue in question is muscle. Because muscle cells lack the glucose-6-phosphatase necessary to produce free glucose from G6P, they cannot be said to perform gluconeogenesis. They do, however, perform glycogenesis through conversion of G6P to glucose-1-phosphate followed by conversion to uridine diphosphateglucose for addition to a growing molecule of glycogen. 

Example Question #21 : Glycolysis

The following are the common substrates, enzymes, and their associated products.  

In patients with a hypoglycemic crisis, the cells are not getting enough glucose for ATP production. Which of the following carbohydrates would be most beneficial during such crisis?

Possible Answers:

Galactose

Sucrose

Maltose

Cellulose 

Lactose 

Correct answer:

Sucrose

Explanation:

Sucrose is the linking of glucose and fructose. Recall from the glycolytic pathway that fructose is further downstream than glucose, and therefore would allow for faster production of ATP.  

Example Question #2 : Glycolysis Carbohydrate Intermediates

What is the major product of the first committed step of glycolysis?

Possible Answers:

Fructose-6-phosphate 

Fructose-1,6-bisphosphate

Glucose-6-phosphate

Pyruvate

Glucose

Correct answer:

Fructose-1,6-bisphosphate

Explanation:

First, we must realize that the first committed step is the first irreversible reaction of glycolysis that is unique to glycolysis (cannot lead to another process, such as the pentose phosphate pathway). This is the third step, in which fructose-6-phosphate is converted to fructose-1,6-bisphosphate (the correct answer).  

Glucose is the beginning reactant of glycolysis, and pyruvate is the final product. Glucose-6-phosphate is the product of the first step of glycolysis overall, but not of the committed step.

Example Question #3 : Glycolysis Carbohydrate Intermediates

In glycolysis, which of these reactions produce adenosine triphosphate (ATP)?

I. Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate

II. Conversion of phosphoenolpyruvate to pyruvate

IV. Conversion of 2-phosphoglycerate to phosphoenolpyruvate.

Possible Answers:

I only

I, II, and III

I and II

II and III

II only

Correct answer:

I and II

Explanation:

Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate is mediated by phosphoglycerate kinase. Conversion of phosphoenolpyruvate to pyruvate is mediated by pyruvate. In both these reactions adenosine diphosphate (ADP) is converted to ATP via substrate level phosphorylation. Conversion of 2-phosphoglycerate to phosphoenolpyruvate, mediated by enolase, does not produce ATP.

Example Question #24 : Glycolysis

Consider the glycolytic reactions shown in the given figure.

Glycolysis intermediates

In this figure, the first intermediate, glyceraldehyde-3-phosphate, is converted into compound X. Following this, compound X is then converted into 3-phosphoglycerate. What is the identity of compound X?

Possible Answers:

2,3-bisphosphoglycerate

Pyruvate

Dihydroxyacetone phosphate

1,3-bisphosphoglycerate

Phosphoenolpyruvate

Correct answer:

1,3-bisphosphoglycerate

Explanation:

In this question, we're shown a portion of glycolysis. We're asked to identify an intermediate in glycolysis based on the intermediate that comes before it and the one that comes after it.

To answer this, we'll need to know the pathway of glycolysis. The first intermediate shown here, glyceraldehyde-3-phosphate, is acted on by the enzyme glyceraldehyde-3-phosphate dehydrogenase. The product of this reaction is 1,3-bisphosphoglycerate, which is thus the correct answer. This intermediate is then acted on by the enzyme phosphoglycerate kinase to produce 3-phosphoglycerate.

Example Question #25 : Glycolysis

Which of the following is not an intermediate of glycolysis?

Possible Answers:

Fructose-1,6-bisphosphate

Fructose-6-phosphate

Glucose-1,6-bisphosphate

Glucose-6-phosphate

Correct answer:

Glucose-1,6-bisphosphate

Explanation:

As glucose is introduced into the glycolytic pathway, it is first phosphorylated to create glucose-6-phosphate. That will then be converted to fructose-6-phosphate via phosphoglucose isomerase. That product will then be phosphorylated once more via phosphofructokinase-1 to create fructose-1,6-bisphosphate. Glucose-1,6-bisphosphate is never an observed intermediate in glycolysis.

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