GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Glycolysis

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Example Question #1 : Help With Glycolysis

The carbohydrate mannose is not present in the standard glycolytic pathway. It can, however, enter glycolysis by first being converted into another sugar. Which of the following choices represents the point at which mannose first enters the glycolytic pathway?

Possible Answers:

Fuctose-6-phosphate

Glucose

Glucose-6-phosphate

Fuctose-1,6-bisphosphate

Correct answer:

Fuctose-6-phosphate

Explanation:

Mannose enters glycolysis by first being phosphorylated by hexokinase. The newly formed mannose-6-phosphate is then isomerized into fructose-6-phosphate by the enzyme phosphomannose isomerase. The sugar is now in a form that can follow the normal glycolytic pathway.

Example Question #2 : Help With Glycolysis

During the first step of glycolysis, glucose is phosphorylated by hexokinase. What is the purpose of this reaction?

Possible Answers:

The phophorylation of glucose changes the structure of glucose so that it can be isomerized in the next step

The phophorylation of glucose creates a negative charge on the glucose molecule so that it cannot pass through the plasma membrane

The proton released via the phosphorylation reaction is necessary for the formation of NADH

The hydrolysis of ATP is necessary to start the glycolytic pathway

Correct answer:

The phophorylation of glucose creates a negative charge on the glucose molecule so that it cannot pass through the plasma membrane

Explanation:

If glucose was not phosphorylated, it would be free to diffuse through the plasma membrane and leave the cell. This situation would not be good for the cell because the reaction cannot continue outside of the cytosol. The negative charge created by the phosphorylation prevents the glucose molecule from crossing the plasma membrane due to the similar charge at the plasma membrane. 

Example Question #3 : Help With Glycolysis

What does it mean to say that glycolysis has an energy investment phase?

Possible Answers:

ATP must be used in order to create the NADH in glycolysis

ATP must be used in order to move the glucose into the cytosol

ATP must be used in order to prepare the glucose molecule to be split

There is a net loss of ATP in glycolysis

Correct answer:

ATP must be used in order to prepare the glucose molecule to be split

Explanation:

Glycolysis can be divided into two parts: the energy investment phase and the energy payoff phase. The energy investment phase comes first when glucose is phosphorylated twice, requiring the use of two molecules of ATP. After the glucose is split, four molecules of ATP will be made in the final steps. This results in a net gain of two ATP in glycolysis, but ATP must be spent prior to being made.

Example Question #4 : Help With Glycolysis

What molecule is the critical product of fermentation that is reinvested in glycolysis?

Possible Answers:

Glucose

ADP

NAD+

NADH

Correct answer:

NAD+

Explanation:

During glycolysis, a total of two molecules of NAD+ are reduced in order to form two NADH molecules. These NAD+ molecules need to be regenerated in order for more glycolytic reactions to take place; otherwise, the process would come to a halt. Fermentation takes care of this problem in anaerobic environments by oxidizing excess NADH (since it is no longer utilized in the electron transport chain) into NAD+, which is then returned to the cytosol where it can be used again in glycolysis.

Example Question #5 : Cellular Respiration And Photosynthesis

In what cellular compartment does the process of glycolysis occur?

Possible Answers:

Mitochondrial outer membrane

Cytosol

Nucleus

Mitochondrial inner membrane

Endoplasmic reticulum

Correct answer:

Cytosol

Explanation:

Both phases of glycolysis occur in the cytosol of the cell. The products of glycolysis are moved for further processing into the mitochondria, but the conversion of glucose to pyruvate is a cytosolic reaction. 

Example Question #6 : Cellular Respiration And Photosynthesis

Glycolysis converts molecules of glucose into pyruvate. Glycolysis consists of two phases: the preparatory phase (which consumes ATP) and the pay-off phase (which produces ATP). Which of these correctly indicates the number of ATPs consumed in the preparatory phase, and the number of ATPs generated in the pay-off phase of anaerobic glycolysis. 

Possible Answers:

2 ATP consumed, 4 ATP produced

3 ATP consumed, 3 ATP produced

6 ATP consumed, 2 ATP produced

2 ATP consumed, 2 ATP produced

4 ATP consumed, 2 ATP produced

Correct answer:

2 ATP consumed, 4 ATP produced

Explanation:

The initial energy investment required for conversion of one glucose to pyruvate is 2 ATP in the preparatory phase. In the pay-off phase, substrate level phosphorylation produces a total of 4 ATP per initial glucose. 

Example Question #5 : Help With Glycolysis

Pyruvate must be oxidized into acetyl-CoA in order to enter the citric acid cycle. Which of the following answers contains the inputs required for this process per one molecule of pyruvate? 

Possible Answers:

, coenzyme A

Correct answer:

, coenzyme A

Explanation:

 and  are the resultant molecules from this conversion, not the inputs.  and  are important molecules in the citric acid cycle, but are not required for this particular oxidation step.  must be reduced to , and coenzyme A is a crucial modulator of these reactions. Thus,  and coenzyme A are the required inputs for the oxidation of pyruvate to acetyl CoA. 

Example Question #1 : Help With Glycolysis

A student isolates starch and provides it as nutrients to a cell culture in anaerobic conditions. What additional steps, if any, does the student have to take to facilitate energy production in the cells?

Possible Answers:

The student has to add glycogen instead of starch

The student has to provide aerobic conditions instead

The student has to add glucosidases

The student has to do nothing; the cells will utilize starch and produce energy

Correct answer:

The student has to add glucosidases

Explanation:

Starch is a complex carbohydrate that is digested by enzymes in the small intestine. These digestive enzymes, called glucosidases, are released by exocrine glands in humans and are involved in breakdown of complex carbohydrates to their individual monomers (glucose). Recall that energy production in cell begins with glycolysis, where a molecule of glucose is metabolized to produce intermediates for subsequent metabolic steps. Cells can’t use starch or glycogen during glycolysis; therefore, the student must add glucosidase to break down starch into individual glucose molecules.

Energy can be produced in anaerobic conditions (like in glycolysis). It might not have a high yield of energy such as aerobic respiration, but the cells can still produce energy when they are oxygen deficient. As mentioned, glycogen is a complex carbohydrate; therefore, adding it without glucosidase will not help facilitate energy production.

Example Question #9 : Cellular Respiration And Photosynthesis

Anaerobic metabolism occurs in the __________; fermentation occurs in the __________.

Possible Answers:

cytoplasm . . . mitochondria

cytoplasm . . . cytoplasm

mitochondria . . . mitochondria

mitochondria . . . cytoplasm

Correct answer:

cytoplasm . . . cytoplasm

Explanation:

Anaerobic metabolism, such as glycolysis and fermentation, occur in the cellular cytoplasm. The products of glycolysis are transported to the mitochondria where they undergo Krebs cycle (in mitochondrial matrix) and oxidative phosphorylation (on the inner mitochondrial membrane). Both Krebs cycle and oxidative phosphorylation require oxygen and are, therefore, called aerobic metabolism.

Example Question #7 : Help With Glycolysis

Which of the following is true regarding glycolysis?

Possible Answers:

FAD is reduced during glycolysis

More than one of these are true

ATP is produced but not utilized during glycolysis

All of the carbons from the glycolysis input are transferred to pyruvate 

Correct answer:

All of the carbons from the glycolysis input are transferred to pyruvate 

Explanation:

Glycolysis is an anaerobic process that produces 2 net ATP, 2 pyruvate molecules, and 2 NADH. Pyruvate is a three-carbon molecule. Recall that glucose is a six-carbon molecule; therefore, the six-carbon glucose is broken down to two three-carbon pyruvate molecules. This means that all the carbons in glucose are transferred to the pyruvate molecules. ATP is produced and consumed in glycolysis. There is a total of four ATP molecules synthesized in the glycolysis; however, glycolysis consume two ATP molecules so you get a net of 2 ATP molecules. Finally, glycolysis involves the reduction two  molecules to yield two NADH molecules (not FAD).

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