Carbohydrate Synthesis - Biochemistry
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The pentose phosphate pathway is an important metabolic pathway within cells that allows them to synthesize two essential products. What are these two products, and what do they do?
The pentose phosphate pathway is an important metabolic pathway within cells that allows them to synthesize two essential products. What are these two products, and what do they do?
The pentose phosphate pathway (PPP) is a metabolic pathway in cells that is used to generate NADPH and/or ribose-5-phosphate for use in the cell, depending on the cell's needs. NADPH is used primarily to provide reducing power for several biosynthetic reactions, but it also serves as a means to keep glutathione predominately in its reduced form in the cell. This, in turn, helps maintain a reducing environment within cells. Furthermore, ribose-5-phosphate is used as a major precursor for the synthesis of nucleotides.
NADH and FADH2 are not produced by the PPP, but rather are produced by the oxidation of glucose via the aerobic respiration pathway. These two molecules are carriers of high-energy electrons, which are used to generate ATP via the electron transport chain.
Glutathione, as mentioned previously, is not produced by the PPP; however, it does use the NADPH produced by the PPP to maintain its reduced form within the cell, which, in turn, maintains a predominately reducing environment within the cell. 2,3-bisphosphoglycerate is an intermediate of glycolysis, not the PPP. One major function of 2,3-BPG is to bind hemoglobin and reduce its affinity for O2. This allows red blood cells to have an easier time releasing O2 to tissues that are in need of it.
Fructose-2,6-bisphosphate is not a product of the PPP. Rather, it is produced from a side reaction of the glycolytic intermediate fructose-6-phosphate. Fructose-2,6-bisphosphate serves as an allosteric regulator of the enzyme fructose-1,6-bisphosphatase, which is an important regulatory enzyme for glycolysis and gluconeogenesis. Hormones such as insulin and glucagon can stimulate cells to alter their concentration of fructose-2,6-bisphosphate, which in turn regulates the activity of glycolysis and gluconeogenesis. Glycerol-3-phosphate is also not produced from the PPP. Rather, it can be produced from the phosphorylation of glycerol or from the reduction of dihydroxyacetone phosphate, an intermediate of glycolysis. It is used as the backbone for the formation of triglycerides and phospholipids.
Acetoacetate and beta-hydroxybutyrate are both ketone bodies produced not by the PPP, but from the condensation of two molecules of acetyl-CoA plus additional modifications. Generally, when the body is in a fasting state and needs to reserve blood glucose levels, ketone bodies can be produced to act as an alternative energy source, thus allowing glucose to be mostly spared.
The pentose phosphate pathway (PPP) is a metabolic pathway in cells that is used to generate NADPH and/or ribose-5-phosphate for use in the cell, depending on the cell's needs. NADPH is used primarily to provide reducing power for several biosynthetic reactions, but it also serves as a means to keep glutathione predominately in its reduced form in the cell. This, in turn, helps maintain a reducing environment within cells. Furthermore, ribose-5-phosphate is used as a major precursor for the synthesis of nucleotides.
NADH and FADH2 are not produced by the PPP, but rather are produced by the oxidation of glucose via the aerobic respiration pathway. These two molecules are carriers of high-energy electrons, which are used to generate ATP via the electron transport chain.
Glutathione, as mentioned previously, is not produced by the PPP; however, it does use the NADPH produced by the PPP to maintain its reduced form within the cell, which, in turn, maintains a predominately reducing environment within the cell. 2,3-bisphosphoglycerate is an intermediate of glycolysis, not the PPP. One major function of 2,3-BPG is to bind hemoglobin and reduce its affinity for O2. This allows red blood cells to have an easier time releasing O2 to tissues that are in need of it.
Fructose-2,6-bisphosphate is not a product of the PPP. Rather, it is produced from a side reaction of the glycolytic intermediate fructose-6-phosphate. Fructose-2,6-bisphosphate serves as an allosteric regulator of the enzyme fructose-1,6-bisphosphatase, which is an important regulatory enzyme for glycolysis and gluconeogenesis. Hormones such as insulin and glucagon can stimulate cells to alter their concentration of fructose-2,6-bisphosphate, which in turn regulates the activity of glycolysis and gluconeogenesis. Glycerol-3-phosphate is also not produced from the PPP. Rather, it can be produced from the phosphorylation of glycerol or from the reduction of dihydroxyacetone phosphate, an intermediate of glycolysis. It is used as the backbone for the formation of triglycerides and phospholipids.
Acetoacetate and beta-hydroxybutyrate are both ketone bodies produced not by the PPP, but from the condensation of two molecules of acetyl-CoA plus additional modifications. Generally, when the body is in a fasting state and needs to reserve blood glucose levels, ketone bodies can be produced to act as an alternative energy source, thus allowing glucose to be mostly spared.
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Which of the following carbohydrates cannot be continuously linearized with 
glycosidic bonds?
Which of the following carbohydrates cannot be continuously linearized with
In order to linearize using a 
linkage, there needs to be an unbound carbon on the 1 position. However, sucrose is a 
linkage and doesn't have a carbon available to linearize in the 1 position. It isn't a reducing sugar and therefore cannot be linearized. All of the other sugars have their anomeric carbon located at the 1 position and all of them are reducing sugars that can be linearized.
In order to linearize using a
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The enzyme phosphoglucomutase is an enzyme responsible for the interconversion of glucose-6-phosphate and glucose-1-phosphate. In a person who is fasting, which of the following metabolic pathways is the most likely destination for glucose-6-phosphate?
The enzyme phosphoglucomutase is an enzyme responsible for the interconversion of glucose-6-phosphate and glucose-1-phosphate. In a person who is fasting, which of the following metabolic pathways is the most likely destination for glucose-6-phosphate?
From the question stem, we're told that the enzyme phosphoglucomutase is responsible for interconverting two intermediate forms of glucose, both glucose-1-phosphate and glucose-6-phosphate. We're then asked to determine the most likely metabolic pathway that glucose-6-phosphate would be used for in a fasting individual.
First, it's important to remember that in an individual that is fasting, energy resources become more scarce. Therefore, the body tries to conserve as much energy as it can in this state. Furthermore, since the brain relies mostly on glucose for its metabolism, the body tries to keep a relatively stable level of glucose in the blood. As a result, many tissues in the body switch from using glucose to instead using other energy sources, such as fatty acids or ketone bodies. In order to help ensure that blood levels of glucose remain stable, the liver increases its rate of gluconeogenesis, which generates glucose from non-sugar substrates, such as pyruvic acid, certain amino acids, and glycerol. Therefore, we would expect glucose-6-phosphate to be funneled mostly into the gluconeogenesis pathway.
Even though glucose-6-phosphate can also be diverted to other pathways, such as glycolysis, glycerogenesis, or the pentose phosphate pathway, all of these pathways result in a net consumption of glucose. In a fasting state, this is the opposite of what we would want, since blood glucose levels need to be mostly stabilized in order to ensure that nervous tissue has an adequate supply.
From the question stem, we're told that the enzyme phosphoglucomutase is responsible for interconverting two intermediate forms of glucose, both glucose-1-phosphate and glucose-6-phosphate. We're then asked to determine the most likely metabolic pathway that glucose-6-phosphate would be used for in a fasting individual.
First, it's important to remember that in an individual that is fasting, energy resources become more scarce. Therefore, the body tries to conserve as much energy as it can in this state. Furthermore, since the brain relies mostly on glucose for its metabolism, the body tries to keep a relatively stable level of glucose in the blood. As a result, many tissues in the body switch from using glucose to instead using other energy sources, such as fatty acids or ketone bodies. In order to help ensure that blood levels of glucose remain stable, the liver increases its rate of gluconeogenesis, which generates glucose from non-sugar substrates, such as pyruvic acid, certain amino acids, and glycerol. Therefore, we would expect glucose-6-phosphate to be funneled mostly into the gluconeogenesis pathway.
Even though glucose-6-phosphate can also be diverted to other pathways, such as glycolysis, glycerogenesis, or the pentose phosphate pathway, all of these pathways result in a net consumption of glucose. In a fasting state, this is the opposite of what we would want, since blood glucose levels need to be mostly stabilized in order to ensure that nervous tissue has an adequate supply.
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One of the key enzymes in the pentose phosphate pathway is glucose-6-phosphate dehydrogenase (G6PDH). This enzyme is responsible for oxidizing glucose-6-phosphate into the next intermediate in the pathway, with co-occuring production of NADPH. Which of the following is most likely to be true about the regulation of this enzyme?
One of the key enzymes in the pentose phosphate pathway is glucose-6-phosphate dehydrogenase (G6PDH). This enzyme is responsible for oxidizing glucose-6-phosphate into the next intermediate in the pathway, with co-occuring production of NADPH. Which of the following is most likely to be true about the regulation of this enzyme?
From the question stem, we are told that glucose-6-phosphate dehydrogenase oxidized glucose into another compound, and also produces a molecule of NADPH in the process. In order to determine the way in which this enzyme is likely to be regulated, it's important to consider feedback mechanics.
Since this enzyme is producing NADPH when it is turned on, we would expect this product to negatively regulate the enzyme via feedback inhibition. Moreover, since we know that 
is a reactant, we can correctly assume that having a high concentration of this will likely drive the reaction forward by turning the enzyme on. Thus, 
would be expected to allosterically activate this enzyme. Furthermore, the question stem tells us nothing about the unphosphorylated forms of these cofactors, therefore we have no way of knowing how many NADH or 
affects this enzyme, if they do at all.
From the question stem, we are told that glucose-6-phosphate dehydrogenase oxidized glucose into another compound, and also produces a molecule of NADPH in the process. In order to determine the way in which this enzyme is likely to be regulated, it's important to consider feedback mechanics.
Since this enzyme is producing NADPH when it is turned on, we would expect this product to negatively regulate the enzyme via feedback inhibition. Moreover, since we know that
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One important chemical transformation that occurs in the pentose phosphate pathway is the conversion of glucose-6-phosphate (G6P) to ribulose-5-phosphate (R5P), which is shown below.
The conversion shown above is an example of which of the following type of reaction?
One important chemical transformation that occurs in the pentose phosphate pathway is the conversion of glucose-6-phosphate (G6P) to ribulose-5-phosphate (R5P), which is shown below.
The conversion shown above is an example of which of the following type of reaction?
From the question stem, we are shown the reaction in which glucose-6-phosphate is transformed into ribulose-5-phosphate. We are then asked to determine which type of reaction is occurring in this process.
We can also notice from the reaction that 
is a reactant, and 
is a product. Therefore, the 
is being reduced to form 
. In order for this reduction reaction to happen, there needs to be a simultaneous oxidation reaction occurring, since the electrons need to come from somewhere. In this case, the electrons are coming from glucose-6-phosphate. Therefore, as 
is reduced to 
, glucose-6-phosphate is oxidized to ribulose-5-phosphate. Thus, this is an oxidation reaction.
Also, it's important to note that this is not a carboxylation reaction. In fact, it is actually a decarboxylation reaction, since one of the carbon atoms on glucose is converted into carbon dioxide.
Moreover, this is also not a phosphorylation reaction, as the reactant and products have an equal number of phosphate groups.
And lastly, this is not an isomerization reaction because glucose-6-phosphate and ribulose-5-phosphate have different molecular formulas, thus they cannot ever be structural isomers.
From the question stem, we are shown the reaction in which glucose-6-phosphate is transformed into ribulose-5-phosphate. We are then asked to determine which type of reaction is occurring in this process.
We can also notice from the reaction that
Also, it's important to note that this is not a carboxylation reaction. In fact, it is actually a decarboxylation reaction, since one of the carbon atoms on glucose is converted into carbon dioxide.
Moreover, this is also not a phosphorylation reaction, as the reactant and products have an equal number of phosphate groups.
And lastly, this is not an isomerization reaction because glucose-6-phosphate and ribulose-5-phosphate have different molecular formulas, thus they cannot ever be structural isomers.
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Glycogen is a polysaccharide of which of the following molecules?
Glycogen is a polysaccharide of which of the following molecules?
Glucose is converted into glycogen during the process called glycogenesis. Its structure consists of many linear alpha(1
4) glycosidic bonds, and also many branched alpha(1
6) glycosidic bonds. This heavily-branched structure means that there are many free ends, which are the substrates for glycogen phosphorylase. A debranching enzyme is needed to lyse the alpha(1
6) glycosidic bonds. Cellulose is a polymer glucose linked together via of beta(1
4) glycosidic bonds. Humans lack enzymes to catalyze the lysis of these bonds in cellulose.
Glucose is converted into glycogen during the process called glycogenesis. Its structure consists of many linear alpha(1
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In gluconeogenesis, where is oxaloacetate sequestered, and how is it able to reach the cytoplasm?
In gluconeogenesis, where is oxaloacetate sequestered, and how is it able to reach the cytoplasm?
Oxaloacetate is a metabolite of the citric acid cycle, which takes place in the mitochondrial matrix. Oxaloacetate cannot diffuse across the mitochondrial matrix, but malate can. So oxaloacetate is reduced to malate by malate dehydrogenase, and can now enter into the cytoplasm. Since malate dehydrogenase can catalyze the reverse reaction as well as the forward reaction, it can be used again to reform oxaloacetate. Once in the cytoplasm, oxaloacetate is converted into phosphoenolpyruvate (PEP) and continues gluconeogenesis.
Oxaloacetate is a metabolite of the citric acid cycle, which takes place in the mitochondrial matrix. Oxaloacetate cannot diffuse across the mitochondrial matrix, but malate can. So oxaloacetate is reduced to malate by malate dehydrogenase, and can now enter into the cytoplasm. Since malate dehydrogenase can catalyze the reverse reaction as well as the forward reaction, it can be used again to reform oxaloacetate. Once in the cytoplasm, oxaloacetate is converted into phosphoenolpyruvate (PEP) and continues gluconeogenesis.
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Which of the following is false about the carbon fixation reaction?
Which of the following is false about the carbon fixation reaction?
For each 
molecule converted into carbohydrate, 3 ATPs and 2 NADPHs are consumed. The Calvin cycle is initiated when 
and ribulose 1,5 biphosphate combine. The enzyme ribulose biphospate carboxylase catalyzes the reaction in the stroma of chloroplasts, and is considered one of the most the world's most abundant proteins. Glyceraldehyde 3-phosphate, which is a by-product of the cycle, goes on to be a building block of sugar, fatty acid, and amino acid synthesis.
For each
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What is the major distinction between NADH and NADPH in biochemistry?
What is the major distinction between NADH and NADPH in biochemistry?
The major distinction between NADH and NADPH is that NADH is generally used in catabolic reactions meant to produce ATP. NADPH, on the other hand, is used primarily in anabolic reactions meant to build macromolecules from their smaller parts.
The major distinction between NADH and NADPH is that NADH is generally used in catabolic reactions meant to produce ATP. NADPH, on the other hand, is used primarily in anabolic reactions meant to build macromolecules from their smaller parts.
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In order to be added to a growing glycogen chain, glucose must first be activated by which of the following molecules?
In order to be added to a growing glycogen chain, glucose must first be activated by which of the following molecules?
UDP-glucose is the activated form of glucose that works to build chains of glycogen. The other listed molecules do not serve this function.
UDP-glucose is the activated form of glucose that works to build chains of glycogen. The other listed molecules do not serve this function.
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What two molecules are the links between the urea cycle and gluconeogenesis?
What two molecules are the links between the urea cycle and gluconeogenesis?
Aspartate can form arginosuccinate, which can then release a fumarate molecule. The fumarate can enter into the Krebs cycle and eventually the pathway can lead to gluconeogenesis. The arginine from the arginosuccinate can continue through the urea cycle.
Aspartate can form arginosuccinate, which can then release a fumarate molecule. The fumarate can enter into the Krebs cycle and eventually the pathway can lead to gluconeogenesis. The arginine from the arginosuccinate can continue through the urea cycle.
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What is the role of phosphoenolpyruvate carboxykinase in carbohydrate metabolism?
What is the role of phosphoenolpyruvate carboxykinase in carbohydrate metabolism?
Gluconeogenesis is the production of glucose from other sources than carbohydrates, such as from pyruvate, amino acids, lactate and glycerol. Phosphoenolpyruvate carboxykinase converts oxaloacetate to phosphoenolpyruvate and carbon dioxide. It also produces GDP from GTP. It is regulated by hormones, such as glucagon and cortisol.
Gluconeogenesis is the production of glucose from other sources than carbohydrates, such as from pyruvate, amino acids, lactate and glycerol. Phosphoenolpyruvate carboxykinase converts oxaloacetate to phosphoenolpyruvate and carbon dioxide. It also produces GDP from GTP. It is regulated by hormones, such as glucagon and cortisol.
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What is the net yield from the pentose phosphate pathway?
I. 
II. 
III. 
IV. 
What is the net yield from the pentose phosphate pathway?
I.
II.
III.
IV.
The pentose phosphate pathway produces NADPH and five-carbon sugars. The net reaction is:
The pathway is also important in purine precursor synthesis.
The pentose phosphate pathway produces NADPH and five-carbon sugars. The net reaction is:
The pathway is also important in purine precursor synthesis.
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How does ingestion of high amounts of ethanol affect gluconeogenesis?
I. High amounts of ethanol get oxidized producing NADPH.
II. High levels of NADPH inhibit gluconeogenesis.
III. High levels of NADPH stimulate gluconeogenesis.
IV. High amounts of ethanol get oxidized producing NADP.
How does ingestion of high amounts of ethanol affect gluconeogenesis?
I. High amounts of ethanol get oxidized producing NADPH.
II. High levels of NADPH inhibit gluconeogenesis.
III. High levels of NADPH stimulate gluconeogenesis.
IV. High amounts of ethanol get oxidized producing NADP.
Ingestion of high amounts of ethanol leads to increased NADPH. High levels of NADPH inhibit gluconeogenesis followed by low glucose levels in the absence of dietary intake. In acute ingestion of alcohol, hypoglycemia (low levels of glucose in the blood) can follow due to inhibition of gluconeogenesis.
Ingestion of high amounts of ethanol leads to increased NADPH. High levels of NADPH inhibit gluconeogenesis followed by low glucose levels in the absence of dietary intake. In acute ingestion of alcohol, hypoglycemia (low levels of glucose in the blood) can follow due to inhibition of gluconeogenesis.
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When would you expect glycogen synthase to be activated?
When would you expect glycogen synthase to be activated?
Glycogen synthase is turned on when unphosphorylated. The enzyme responsible for this is protein phosphatase I. Protein kinase A inactivates glycogen synthase. Low glucose concentration causes a release in glucagon, which activates glycogen phosphorylase and deactivates glycogen synthase.
Glycogen synthase is turned on when unphosphorylated. The enzyme responsible for this is protein phosphatase I. Protein kinase A inactivates glycogen synthase. Low glucose concentration causes a release in glucagon, which activates glycogen phosphorylase and deactivates glycogen synthase.
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Which of the following is an oxidoreductase?
Which of the following is an oxidoreductase?
An oxidoreductase catalyzes the transfer of electrons from one molecule to the other, usually using 
; i.e., it is an enzyme that catalyzes a redox reaction. Trypsin cleaves peptide bonds. Hexokinase phosphorylates hexose sugars. Glucose 6-phosphatase hydrolyzes glucose 6-phosphate into a phosphate group and glucose. Aspartate amino-transferase catalyzes the transfer of an amino group between aspartate and glutamate. Lactate dehydrogenase interconverts pyruvate to lactate, and at the same time 
and 
.
An oxidoreductase catalyzes the transfer of electrons from one molecule to the other, usually using
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Given that the pyruvate dehydrogenase complex is product-inhibited, which of the following molecules would act as an inhibitor to it?
Given that the pyruvate dehydrogenase complex is product-inhibited, which of the following molecules would act as an inhibitor to it?
The pyruvate dehydrogenase complex catalyzes the following reaction:
Since it is product inhibited, acetyl-CoA will inhibit the complex.
The pyruvate dehydrogenase complex catalyzes the following reaction:
Since it is product inhibited, acetyl-CoA will inhibit the complex.
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What is the name of the process involved in the conversion of glucose to glycogen?
What is the name of the process involved in the conversion of glucose to glycogen?
The process of glycogenesis is when glucose is converted into glycogen. This occurs in the muscle and the liver after food is consumed. Gluconeogenesis is the process where glucose is produced from non-carbohydrate precursors. Glycogenolysis is the breakdown of glycogen. Glycolysis is the breakdown of glucose into two molecules of pyruvate. The Krebs cycle does not generate glycogen or glucose, rather it produces high energy electrons to be carried to the electron transport chain for ATP production.
The process of glycogenesis is when glucose is converted into glycogen. This occurs in the muscle and the liver after food is consumed. Gluconeogenesis is the process where glucose is produced from non-carbohydrate precursors. Glycogenolysis is the breakdown of glycogen. Glycolysis is the breakdown of glucose into two molecules of pyruvate. The Krebs cycle does not generate glycogen or glucose, rather it produces high energy electrons to be carried to the electron transport chain for ATP production.
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Which reaction occurs during a fasting state when glycogen stores are depleted?
Which reaction occurs during a fasting state when glycogen stores are depleted?
Glyconeogenesis occurs in the hepatic pathway when no glucose is available. The electron transport chain occurs during cellular respiration. Glycolysis is the break down of glucose, not the production of glycogen. The Krebs cycle and citric acid cycle are the same thing, and both are used to produce NADH and ATP.
Glyconeogenesis occurs in the hepatic pathway when no glucose is available. The electron transport chain occurs during cellular respiration. Glycolysis is the break down of glucose, not the production of glycogen. The Krebs cycle and citric acid cycle are the same thing, and both are used to produce NADH and ATP.
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What is the name of the enzyme that is found in the liver that converts glucose into glucose-6-phosphate?
What is the name of the enzyme that is found in the liver that converts glucose into glucose-6-phosphate?
Fructokinase catalyzes the reaction of fructose converting into fructose-1-phosphate. Glycogenin acts as a primer for glycogen synthesis, by polymerizing the first few molecules of glucose. Glycogen synthase converts glucose to glycogen. Phospholipase hydrolyzes phospholipids.
Fructokinase catalyzes the reaction of fructose converting into fructose-1-phosphate. Glycogenin acts as a primer for glycogen synthesis, by polymerizing the first few molecules of glucose. Glycogen synthase converts glucose to glycogen. Phospholipase hydrolyzes phospholipids.
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