Glycolysis Enzymes - Biochemistry
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Which of these enzymes catalyzes the first reaction in glycolysis?
Which of these enzymes catalyzes the first reaction in glycolysis?
The first step in glycolysis is the conversion of glucose to glucose-6-phosphate through the consumption on one ATP molecule. Glucose is reacted upon by the enzyme hexokinase to carry out this step. Kinases are a group of enzymes that add phosphate groups by removing them from an ATP. All of these other enzymes catalyze subsequent reactions in glycolysis.
The first step in glycolysis is the conversion of glucose to glucose-6-phosphate through the consumption on one ATP molecule. Glucose is reacted upon by the enzyme hexokinase to carry out this step. Kinases are a group of enzymes that add phosphate groups by removing them from an ATP. All of these other enzymes catalyze subsequent reactions in glycolysis.
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Dihydroxyacetone is converted to glyceraldehyde-3-phosphate by what category of enzyme?
Dihydroxyacetone is converted to glyceraldehyde-3-phosphate by what category of enzyme?
Dihydroxyacetone phosphate (DHAP) is converted to glyceradehyde-3-phosphate (G3P) by the enzyme triose phosphate isomerase. As the name suggests, this enzyme catalyzes the isomerization of a three-carbon sugar into another three-carbon sugar. Since the molecular formulas of DHAP and G3P are the same, we know that they are isomers of each other.
The balance between DHAP and G3P is extremely important in regulating overall cell metabolism. DHAP is a precursor to triglycerides, and is used in their synthesis, while G3P is an intermediate in glycolysis, an ATP-producing process. In order to favor the conversion of DHAP into G3P, and not the opposite, the cell must keep G3P levels low (Le Chatelier's Principle). Consider the following equilibrium: 
. This should make sense: if there is lots of ATP around in the cell, there is no need for glycolysis to proceed. Thus the equilibrium will be pushed to the left, increasing the concentration of DHAP in the cell. In humans, DHAP is converted into triglycerides, which get stored as fat. One way to shift this equilibrium to the right is to "create" an ATP need. This can be done by exercising. Exercise utilizes ATP and will thus pull the equilibrium to the right, removing DHAP (which was destined to be converted into fat) and facilitates its conversion into G3P to proceed with cellular respiration.
Dihydroxyacetone phosphate (DHAP) is converted to glyceradehyde-3-phosphate (G3P) by the enzyme triose phosphate isomerase. As the name suggests, this enzyme catalyzes the isomerization of a three-carbon sugar into another three-carbon sugar. Since the molecular formulas of DHAP and G3P are the same, we know that they are isomers of each other.
The balance between DHAP and G3P is extremely important in regulating overall cell metabolism. DHAP is a precursor to triglycerides, and is used in their synthesis, while G3P is an intermediate in glycolysis, an ATP-producing process. In order to favor the conversion of DHAP into G3P, and not the opposite, the cell must keep G3P levels low (Le Chatelier's Principle). Consider the following equilibrium:
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The enzyme pyruvate kinase is responsible for catalyzing the conversion of phosphoenolpyruvate into __________.
The enzyme pyruvate kinase is responsible for catalyzing the conversion of phosphoenolpyruvate into __________.
The tenth and final reaction of glycolysis involves the conversion of phosphoenolpyruvate (PEP) into pyruvate. This step is catalyzed by the enzyme pyruvate kinase. This kinase is going to remove a phosphate group from PEP and put it on ADP to yield ATP. Pyruvate, a three-carbon molecule, is the end product of glycolysis. It can be sent to the pyruvate dehydrogenase complex to be turned into acetyl-CoA, which enters the Krebs cycle. Alternatively, it can be reduced into lactate and/or ethanol (depending on the organism) to regenerate 
for glycolysis via anaerobic respiration.
The tenth and final reaction of glycolysis involves the conversion of phosphoenolpyruvate (PEP) into pyruvate. This step is catalyzed by the enzyme pyruvate kinase. This kinase is going to remove a phosphate group from PEP and put it on ADP to yield ATP. Pyruvate, a three-carbon molecule, is the end product of glycolysis. It can be sent to the pyruvate dehydrogenase complex to be turned into acetyl-CoA, which enters the Krebs cycle. Alternatively, it can be reduced into lactate and/or ethanol (depending on the organism) to regenerate
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Which of the ten glucose reactions uses the enzyme GAPDH?
Which of the ten glucose reactions uses the enzyme GAPDH?
Glyceraldehyde phosphate dehydrogenase (GAPDH) is used in the sixth reaction, where G3P is converted to 1,3-bisphosphoglycerate (1,3-BPG). A hydrogen is removed from G3P and added to 
, yielding NADH. Also, G3P has one phosphate group, while 1,3-BPG has two. The energy released as G3P is oxidized (causing subsequent reduction of 
) is highly exergonic. This energy, sometimes referred to as the energy of oxidation, drives the addition of inorganic phosphate onto G3P, yielding the doubly-phosphorylated 1,3-BPG.
Glyceraldehyde phosphate dehydrogenase (GAPDH) is used in the sixth reaction, where G3P is converted to 1,3-bisphosphoglycerate (1,3-BPG). A hydrogen is removed from G3P and added to
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The enzyme enolase catalyzes the ninth reaction of glycolysis. What is the product of this reaction?
The enzyme enolase catalyzes the ninth reaction of glycolysis. What is the product of this reaction?
Theninth reaction involves the conversion of 2-phosphoglycerate into phosphoenolpyruvate. The enzyme enolase, which produces a double bond by removing the hydroxyl group on 2-phosphoglycerate catalyzes this reaction. Note that the resulting molecule is an enol (double bond -ene, and alcohol - ol).
Theninth reaction involves the conversion of 2-phosphoglycerate into phosphoenolpyruvate. The enzyme enolase, which produces a double bond by removing the hydroxyl group on 2-phosphoglycerate catalyzes this reaction. Note that the resulting molecule is an enol (double bond -ene, and alcohol - ol).
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Which of the following best describes the action of an isomerase?
Which of the following best describes the action of an isomerase?
Isomerases catalyze the isomerization, or rearrangement of atoms within a molecule, of its substrate. Isomerases are seen in glycolysis inn the second step where glucose-6-phosphate is converted into fructose-6-phosphate by phosphoglucose isomerase. Glucose-6-phosphate is rearranged into fructose-6-phosphate such that the molecular formula is unchanged. Another isomerase is triose phosphate isomerase. It catalyzes the isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate.
Isomerases catalyze the isomerization, or rearrangement of atoms within a molecule, of its substrate. Isomerases are seen in glycolysis inn the second step where glucose-6-phosphate is converted into fructose-6-phosphate by phosphoglucose isomerase. Glucose-6-phosphate is rearranged into fructose-6-phosphate such that the molecular formula is unchanged. Another isomerase is triose phosphate isomerase. It catalyzes the isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate.
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Which enzyme in glycolysis is responsible for the conversion of glucose to glucose 6-phosphate?
Which enzyme in glycolysis is responsible for the conversion of glucose to glucose 6-phosphate?
Hexokinase is the first enzyme in the glycolytic pathway and it is responsible for the phosphorylation of glucose to glucose 6-phosphate. The other enzymes catalyze subsequent reactions in glycolysis.
Hexokinase is the first enzyme in the glycolytic pathway and it is responsible for the phosphorylation of glucose to glucose 6-phosphate. The other enzymes catalyze subsequent reactions in glycolysis.
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Which of the following enzymes catalyzes the rate-limiting step of glycolysis?
Which of the following enzymes catalyzes the rate-limiting step of glycolysis?
The rate-limiting step of glycolysis is the conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is catalyzed by the enzyme phosphofructokinase. Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, pyruvate kinase converts Phosphoenolpyruvate to pyruvate, and lactate dehydrogenase converts pyruvate into lactose.
The rate-limiting step of glycolysis is the conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is catalyzed by the enzyme phosphofructokinase. Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, pyruvate kinase converts Phosphoenolpyruvate to pyruvate, and lactate dehydrogenase converts pyruvate into lactose.
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Which of the following enzymes carries out a redox reaction in glycolysis?
Which of the following enzymes carries out a redox reaction in glycolysis?
Glyceraldehyde 3-phosphate dehydrogenase is the only enzyme in glycolysis that carries out a redox reaction. Glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate while 
is reduced to 
.
Glyceraldehyde 3-phosphate dehydrogenase is the only enzyme in glycolysis that carries out a redox reaction. Glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate while
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Which of the following choices is responsible for the decarboxylation in the pyruvate dehydrogenase complex?
Which of the following choices is responsible for the decarboxylation in the pyruvate dehydrogenase complex?
The pyruvate dehydrogenase complex essentially carries out a two part reaction: a decarboxylation and an oxidation. All these choices play important roles in the pyruvate dehydrogenase complex. Thiamine pyrophosphate (TPP) is the only choice, however, that is responsible for the decarboxylation step. Lipoamide acts as transporter, transferring the substrate to a distant active site. FAD then reoxidizes lipoamide for the next substrate. CoA is important in producing the substrate.
The pyruvate dehydrogenase complex essentially carries out a two part reaction: a decarboxylation and an oxidation. All these choices play important roles in the pyruvate dehydrogenase complex. Thiamine pyrophosphate (TPP) is the only choice, however, that is responsible for the decarboxylation step. Lipoamide acts as transporter, transferring the substrate to a distant active site. FAD then reoxidizes lipoamide for the next substrate. CoA is important in producing the substrate.
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Which of the following enzymes is found in glycolysis?
Which of the following enzymes is found in glycolysis?
To see which of the enzymes in these answer choices may by in glycolysis, let's go through each one and look at their function.
Aldolase - This enzyme is indeed involved in glycolysis. It is responsible for the cleavage of fructose-1,6-bisphosphate into two products, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Thiolase - This enzyme catalyzes the the reversible association of two acetyl-CoA molecules into acetoacetyl-CoA. This is an important part of the mevalonate pathway as well as beta oxidation and ketone body synthesis/degradation.
Fructose-1,6-bisphosphatase - This enzyme is important in gluconeogenesis, a metabolic pathway that runs counter to glycolysis. Although many of the enzymes found in glycolysis are also used in gluconeogenesis, this enzyme is one example of an exception because it bypasses one of the irreversible reactions from glycolysis.
Aconitase - This enzyme is found in the citric acid cycle. Its function is to convert citrate into its isomer, isocitrate.
To see which of the enzymes in these answer choices may by in glycolysis, let's go through each one and look at their function.
Aldolase - This enzyme is indeed involved in glycolysis. It is responsible for the cleavage of fructose-1,6-bisphosphate into two products, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Thiolase - This enzyme catalyzes the the reversible association of two acetyl-CoA molecules into acetoacetyl-CoA. This is an important part of the mevalonate pathway as well as beta oxidation and ketone body synthesis/degradation.
Fructose-1,6-bisphosphatase - This enzyme is important in gluconeogenesis, a metabolic pathway that runs counter to glycolysis. Although many of the enzymes found in glycolysis are also used in gluconeogenesis, this enzyme is one example of an exception because it bypasses one of the irreversible reactions from glycolysis.
Aconitase - This enzyme is found in the citric acid cycle. Its function is to convert citrate into its isomer, isocitrate.
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The enzyme hexokinase catalyzes the first step of glycolysis, and is crucial to initiating the process and preventing the initial substrate from easily traveling out of the cell (as its pre-reaction structure is membrane permeable). Specifically in the context of glycolysis, what are the names of hexokinase's substrate and product, respectively?
The enzyme hexokinase catalyzes the first step of glycolysis, and is crucial to initiating the process and preventing the initial substrate from easily traveling out of the cell (as its pre-reaction structure is membrane permeable). Specifically in the context of glycolysis, what are the names of hexokinase's substrate and product, respectively?
Hexokinase initiates the first step of glycolysis, which we know is the series of reactions by which glucose is processed to enter the citric acid cycle, and generate energy for the cell. So, in the case of glycolysis, glucose is the substrate of hexokinase. Based upon the name of the enzyme, we can infer that it phosphorylates a six-carbon molecule (which glucose is). By knowing the substrate is glucose, the correct product is glucose-6-phosphate, since its name indicates phosphorylation (addition of a phosphate group) to one of its carbons. Glycogen, fructose, and ATP are not involved in this first step of glycolysis.
Hexokinase initiates the first step of glycolysis, which we know is the series of reactions by which glucose is processed to enter the citric acid cycle, and generate energy for the cell. So, in the case of glycolysis, glucose is the substrate of hexokinase. Based upon the name of the enzyme, we can infer that it phosphorylates a six-carbon molecule (which glucose is). By knowing the substrate is glucose, the correct product is glucose-6-phosphate, since its name indicates phosphorylation (addition of a phosphate group) to one of its carbons. Glycogen, fructose, and ATP are not involved in this first step of glycolysis.
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Which enzyme catalyzes the rate-limiting step of glycolysis?
Which enzyme catalyzes the rate-limiting step of glycolysis?
Hexokinase, pyruvate kinase, and PFK are regulatory enzymes in glycolysis, but PFK catalyzes the rate-limiting step (the phosphorylation of fructose-6-phosphate). Citrate synthase and isocitrate dehydrogenase are involved in the Krebs cycle, not glycolysis.
Hexokinase, pyruvate kinase, and PFK are regulatory enzymes in glycolysis, but PFK catalyzes the rate-limiting step (the phosphorylation of fructose-6-phosphate). Citrate synthase and isocitrate dehydrogenase are involved in the Krebs cycle, not glycolysis.
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Which one of these applies to the enzyme glucokinase?
Which one of these applies to the enzyme glucokinase?
Glucokinase specifically phosphorylates the six-carbon sugar glucose. It is involved in glycolysis, but only in hepatocytes; hexokinase is the main enzyme that phosphorylates glucose during the first reaction of glycolysis. Rather, glucokinase's main role is to phosphorylate glucose to glucose-1-phosphate during the process of glycogen synthesis. The other kinases involved in glycolysis is phosphofructokinase. Fructose and mannose are not phosphorylated by glucokinase. Also, note that hexokinase has a higher affinity for glucose than does glucokinase.
Glucokinase specifically phosphorylates the six-carbon sugar glucose. It is involved in glycolysis, but only in hepatocytes; hexokinase is the main enzyme that phosphorylates glucose during the first reaction of glycolysis. Rather, glucokinase's main role is to phosphorylate glucose to glucose-1-phosphate during the process of glycogen synthesis. The other kinases involved in glycolysis is phosphofructokinase. Fructose and mannose are not phosphorylated by glucokinase. Also, note that hexokinase has a higher affinity for glucose than does glucokinase.
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Which of the following is true of phosphofructokinase (PFK)?
Which of the following is true of phosphofructokinase (PFK)?
Phosphofructokinase catalyzes the third step in glycolysis transforming fructose 6-phosphate to fructose-1,6-bisphosphate. It is an irreversible step, and it is one of the major regulatory points of glycolysis. One way in which it controls the flow of glycolysis is that when there is a high level of ATP, PFK is inhibited. This is because the ultimate goal of glycolysis is to make ATP. Thus, if there is already a high level of ATP, glycolysis should slow down.
Phosphofructokinase catalyzes the third step in glycolysis transforming fructose 6-phosphate to fructose-1,6-bisphosphate. It is an irreversible step, and it is one of the major regulatory points of glycolysis. One way in which it controls the flow of glycolysis is that when there is a high level of ATP, PFK is inhibited. This is because the ultimate goal of glycolysis is to make ATP. Thus, if there is already a high level of ATP, glycolysis should slow down.
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Which of the following enzymes catalyzes an unfavorable step in glycolysis?
Which of the following enzymes catalyzes an unfavorable step in glycolysis?
Hexokinase catalyzes the first step of glycolysis, and this step requires the input of an ATP molecule. This step is unfavorable, but the steps catalyzed by the rest of the enzymes listed as answer choices are favorable.
Hexokinase catalyzes the first step of glycolysis, and this step requires the input of an ATP molecule. This step is unfavorable, but the steps catalyzed by the rest of the enzymes listed as answer choices are favorable.
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Which enzyme in glycolysis is responsible for the cleavage of a six-carbon molecule into two separate three-carbon molecules?
Which enzyme in glycolysis is responsible for the cleavage of a six-carbon molecule into two separate three-carbon molecules?
In the fourth step of glycolysis, the six-carbon molecule fructose-1,6-bisphosphate is cleaved into two separate three-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. This is catalyzed by the enzyme, aldolase.
In the fourth step of glycolysis, the six-carbon molecule fructose-1,6-bisphosphate is cleaved into two separate three-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. This is catalyzed by the enzyme, aldolase.
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If a cell is completely lacking in the enzyme triose phosphate isomerase, which of the following is a possible result?
If a cell is completely lacking in the enzyme triose phosphate isomerase, which of the following is a possible result?
Triose phosphate isomerase is responsible for converting dihydroxyacetone phosphate into glyceraldehyde-3-phosphate. It is glyceraldehyde-3-phosphate that continues on through glycolysis to ultimately form a pyruvate molecule. Therefore, if there is no triose phosphate isomerase, the dihydroxyacetone will be unable to continue through glycolysis. The normal net yield of 2 ATP will be halved, the production of NADH will be halved, and only 1 pyruvate molecule will be created. Glycolysis will still be able to function, and the energy investment phase will be unaffected.
Triose phosphate isomerase is responsible for converting dihydroxyacetone phosphate into glyceraldehyde-3-phosphate. It is glyceraldehyde-3-phosphate that continues on through glycolysis to ultimately form a pyruvate molecule. Therefore, if there is no triose phosphate isomerase, the dihydroxyacetone will be unable to continue through glycolysis. The normal net yield of 2 ATP will be halved, the production of NADH will be halved, and only 1 pyruvate molecule will be created. Glycolysis will still be able to function, and the energy investment phase will be unaffected.
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What is the role of phosphofructokinase-2 in glycolysis?
What is the role of phosphofructokinase-2 in glycolysis?
Phosphofructokinase-2 converts fructose-6-phosphate to fructose-2,6-bisphosphate. The product, fructose-2,6-bisphosphate activates phosphofructokinase-1, the rate limiting step in glycolysis. Phosphofructokinase-2 is regulated by insulin (activated) and glucagon (inhibited).
Phosphofructokinase-2 converts fructose-6-phosphate to fructose-2,6-bisphosphate. The product, fructose-2,6-bisphosphate activates phosphofructokinase-1, the rate limiting step in glycolysis. Phosphofructokinase-2 is regulated by insulin (activated) and glucagon (inhibited).
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