Biochemistry : Glycolysis Regulation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Glycolysis Regulation

The enzyme phosphofructokinase is an important enzyme that plays a significant regulatory role in glycolysis. Which of the following conditions would be expected to result in increased activity of this enzyme?

Possible Answers:

High levels of NADH

High levels of citric acid cycle intermediates

Low levels of ADP

None of these

Low levels of ATP

Correct answer:

Low levels of ATP

Explanation:

We're told in the question stem that phosphofructokinase is an important regulatory enzyme for the glycolysis pathway. In this pathway, glucose is partially oxidized to provide energy for the cell. Therefore, when the cell has plenty of energy available to meet its metabolic needs, the activity of phosphofructokinase will be reduced in order to suppress glycolysis. Alternatively, when the cell is in need of energy, it will turn glycolysis on by increasing the activity of this enzyme. Thus, compounds that indicate the cell has a lot of energy available, such as ATP and NADH, would be expected to be allosteric inhibitors of this enzyme. So, if the cell has a low amount of ATP, the energy carrying molecule, we would expect the activity of this enzyme to be high. High levels of NADH and citric acid cycle intermediates signal that the cell has enough energy, therefore these would serve to reduce the activity of this enzyme. Low levels of ADP would signal that the cell most likely has a high amount of ATP and is thus in a state of energy surplus. Consequently, this scenario would likely reduce the activity of this enzyme.

Example Question #2 : Glycolysis Regulation

Which of the following choices will result in continuous glycolysis?

Possible Answers:

ATP binding to the allosteric site on pyruvate kinase

Loss of allosteric binding site for fructose-1,6-bisphosphate on pyruvate kinase

Loss of allosteric binding site for ATP on phosphofructokinase-1 (PFK-1)

Loss of allosteric binding site for fructose-2,6-bisphosphate on phosphofructokinase-1 (PFK-1)

Correct answer:

Loss of allosteric binding site for ATP on phosphofructokinase-1 (PFK-1)

Explanation:

When there are high levels of ATP in the blood, ATP itself can act as a signal for the inhibition of ATP production. phosphofructokinase-1 (PFK-1) and pyruvate kinase are major sites of glycolytic regulation. ATP can inhibit these enzymes by binding to their allosteric sites. If these allosteric binding sites are lost, ATP can never bind, and glycolysis will continue indefinitely. Conversely, glycolytic intermediates (like fructose-1,6-bisphosphate) and glycolytic activators (like fructose-2,6-bisphosphate) can act on the same enzymes to increase their activity. Loss of allosteric binding sites for fructose-1,6-bisphosphate and fructose-2,6-bisphosphate on pyruvate kinase and PFK-1, respectively, will result in the slowing down or inhibition of glycolysis.

Example Question #3 : Glycolysis Regulation

All of the following stimulate glycolysis except __________.

Possible Answers:

high level of carbon dioxide

decreased pH level

decresed level of ATP

increased level of pyruvate

increased level of AMP

Correct answer:

increased level of pyruvate

Explanation:

Glycolysis will be stimulated in situations that require the body to make more ATP.  When the pH is low, ATP is depleted, AMP is at high levels, and carbon dioxide is increased, the body is likely going to need more of an energy supply.  All of these are related to exercise - a situation in which more ATP will be required.  However, an increase in levels of pyruvate implies that glycolysis is actually backed up and should not be stimulated.

Example Question #4 : Glycolysis Regulation

Fructose-2,6-bisphosphate will strongly upregulate which of the following enzymes?

Possible Answers:

Fructose-2,6-bisphosphatase (FBPase-2)

Fructose-1,6-bisphosphatase (FBPase-1)

Phosphofructokinase-2 (PFK-2)

Phosphofructokinase-1 (PFK-1)

Correct answer:

Phosphofructokinase-1 (PFK-1)

Explanation:

While phosphofructokinase-2 is responsible for creating fructose-2,6-bisphosphate, this molecule will actually upregulate the enzymatic activity of phosphofructokinase-1 (PFK-1). As a result, fructose-2,6-bisphosphate is responsible for increasing the amount of glycolysis done in cells via activation of the glycolytic enzyme PFK-1. 

Example Question #5 : Glycolysis Regulation

Glycolysis is an energy producing process that breaks down glucose. 

In glycolysis, feedback regulation is seen in which of the following examples?

Possible Answers:

AMP inhibiting PFK-1 (phosphofructokinase-1) 

ATP inhibiting PFK-1 (phosphofructokinase-1) 

Insulin inhibiting pyruvate kinase.

Fructose-1,6-bisphosphate inhibiting pyruvate kinase

Hexokinase inhibited by ATP 

Correct answer:

ATP inhibiting PFK-1 (phosphofructokinase-1) 

Explanation:

Feedback inhibition is a process by which the products of a reaction or series of reactions slows, stops or inhibits one of the previous reactions in the process, thereby controlling the rate of reaction, and rate of formation of the products.

In glycolysis, one of the end products is energy in the form of ATP. ATP acts as an inhibitor of phosphofructokinase-1, one of the main rate limiting enzymes in glycolysis. 

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