Protein Catabolism - Biochemistry
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Phenylketonuria is a genetic disorder resulting in a lack of phenylalanine hydroxylase activity. During the first step of phenylalanine metabolism, phenylalanine is hydroxylated into what amino acid?
Phenylketonuria is a genetic disorder resulting in a lack of phenylalanine hydroxylase activity. During the first step of phenylalanine metabolism, phenylalanine is hydroxylated into what amino acid?
The first step in phenylalanine metabolism is conversion of phenylalanine to tyrosine. Tyrsoine is simply a hydroxylated version of phenylalanine.
The first step in phenylalanine metabolism is conversion of phenylalanine to tyrosine. Tyrsoine is simply a hydroxylated version of phenylalanine.
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Which enzyme catalyzes the rate-limiting step of the urea cycle?
Which enzyme catalyzes the rate-limiting step of the urea cycle?
Carbamoyl phosphate synthetase is the rate-limiting step of the urea cycle. It is the first step of the urea cycle and occurs exclusive in the mitochondria of hepatic and renal cells.
Carbamoyl phosphate synthetase is the rate-limiting step of the urea cycle. It is the first step of the urea cycle and occurs exclusive in the mitochondria of hepatic and renal cells.
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Phenylketonuria is a genetic disorder resulting in a lack of phenylalanine hydroxylase activity. During the first step of phenylalanine metabolism, phenylalanine is hydroxylated into what amino acid?
Phenylketonuria is a genetic disorder resulting in a lack of phenylalanine hydroxylase activity. During the first step of phenylalanine metabolism, phenylalanine is hydroxylated into what amino acid?
The first step in phenylalanine metabolism is conversion of phenylalanine to tyrosine. Tyrsoine is simply a hydroxylated version of phenylalanine.
The first step in phenylalanine metabolism is conversion of phenylalanine to tyrosine. Tyrsoine is simply a hydroxylated version of phenylalanine.
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What is produced in one turn of the urea cycle?
What is produced in one turn of the urea cycle?
2 molecules of ammonia and 1 molecule of carbon dioxide are converted into 1 molecule of urea in every turn of the urea cycle. In addition, each cycle regenerates 1 molecule of ornithine for use in the next turn.
2 molecules of ammonia and 1 molecule of carbon dioxide are converted into 1 molecule of urea in every turn of the urea cycle. In addition, each cycle regenerates 1 molecule of ornithine for use in the next turn.
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Which process eliminates nitrogen waste generated from protein catabolism in humans?
Which process eliminates nitrogen waste generated from protein catabolism in humans?
Removal of the amino group is a primary step in amino acid catabolism. Humans (and some other animals) utilize the urea cycle to convert the unnecessary amino groups from amino acids into urea. The carbon skeletons will be fed into the citric acid cycle, and none of the other answers directly relate to human nitrogen metabolism. The Krebs cycle (also known as the citric acid cycle) is an intermediate between glycolysis and oxidative phosphorylation, and involves energy production. Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate organic substrates. The purine nucleotide cycle involves conversion of nucleotides into Krebs cycle intermediates, and makes ammonia as a byproduct, which is then shunted into the urea cycle to be converted into urea and excreted in the urine.
Removal of the amino group is a primary step in amino acid catabolism. Humans (and some other animals) utilize the urea cycle to convert the unnecessary amino groups from amino acids into urea. The carbon skeletons will be fed into the citric acid cycle, and none of the other answers directly relate to human nitrogen metabolism. The Krebs cycle (also known as the citric acid cycle) is an intermediate between glycolysis and oxidative phosphorylation, and involves energy production. Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate organic substrates. The purine nucleotide cycle involves conversion of nucleotides into Krebs cycle intermediates, and makes ammonia as a byproduct, which is then shunted into the urea cycle to be converted into urea and excreted in the urine.
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The first step in the metabolism of most amino acids is the removal of the amino group by aminotransferases. What is the product of this reaction?
The first step in the metabolism of most amino acids is the removal of the amino group by aminotransferases. What is the product of this reaction?
Aminotransferases (transaminases) catalyze the conversion of an amino acid to an 
-keto acid. To do so, they utilize a pyridoxyl phosphate coenzyme, which mediates the transfer of the amino group, leaving a ketone functional group next to the carboxyl group. This 
-keto acid is the product. Since the amino group in an amino acid is attached to the alpha carbon, it will not be a 
-keto acid. Some of the other answer choices give intermediates of the reaction mechanism, not the product.
Aminotransferases (transaminases) catalyze the conversion of an amino acid to an
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Which amino acid cannot be deaminated in protein catabolism?
Which amino acid cannot be deaminated in protein catabolism?
Due to its amino group's location within the pyrrole ring derivative, proline is unable to be deaminated via the aminotransferase step of protein catabolism. Proline oxidase is the enzyme that catalyzes the first reaction in the catabolism of proline. None of the other amino acid answer choices have this limitation.
Due to its amino group's location within the pyrrole ring derivative, proline is unable to be deaminated via the aminotransferase step of protein catabolism. Proline oxidase is the enzyme that catalyzes the first reaction in the catabolism of proline. None of the other amino acid answer choices have this limitation.
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How is most of the ammonium waste removed from the body?
How is most of the ammonium waste removed from the body?
When proteins and amino acids are broken down in the body, ammonium is created as a byproduct. Ammonium is dangerous when it remains free in the human body, so something must be done to get rid of it. The major route of removal of ammonium by the body is via urea synthesis in the liver. Urea can then be excreted in urine.
When proteins and amino acids are broken down in the body, ammonium is created as a byproduct. Ammonium is dangerous when it remains free in the human body, so something must be done to get rid of it. The major route of removal of ammonium by the body is via urea synthesis in the liver. Urea can then be excreted in urine.
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Which of the following is a possible consequence of an arginase deficiency?
Which of the following is a possible consequence of an arginase deficiency?
Arginase catalyzes the conversion of arginine to ornithine and urea. Therefore, if there is a deficiency in arginase, there will be a buildup of arginine, and a deficiency in ornithine and urea. Without the ability to form urea, the ammonium waste from protein and amino acids degradation will not be able to be converted to urea safely. The buildup of ammonium will cause hyperammonemia, which results in some unfavorable physiological scenarios.
Arginase catalyzes the conversion of arginine to ornithine and urea. Therefore, if there is a deficiency in arginase, there will be a buildup of arginine, and a deficiency in ornithine and urea. Without the ability to form urea, the ammonium waste from protein and amino acids degradation will not be able to be converted to urea safely. The buildup of ammonium will cause hyperammonemia, which results in some unfavorable physiological scenarios.
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The urea cycle is vital to the excretion of ammonia, a harmful byproduct of amino acid breakdown.
What enzyme in the urea cycle converts L-ornithine to L-citrulline?
The urea cycle is vital to the excretion of ammonia, a harmful byproduct of amino acid breakdown.
What enzyme in the urea cycle converts L-ornithine to L-citrulline?
Ornithine transcarbamylase catalyzes the reaction between the substrates ornithine and carbamoyl phosphate to form citrulline and phosphate. This process occurs primarily in the hepatic mitochondria, and to a lesser extent in the mitochondria of the renal cells.
Ornithine transcarbamylase catalyzes the reaction between the substrates ornithine and carbamoyl phosphate to form citrulline and phosphate. This process occurs primarily in the hepatic mitochondria, and to a lesser extent in the mitochondria of the renal cells.
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What enzyme is deficient in Lesch-Nyhan syndrome?
What enzyme is deficient in Lesch-Nyhan syndrome?
Lesch-Nyhan syndrome is an x-linked deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). HGPRT plays a central role in the generation of purine nucleotides through the purine salvage pathway. Cell breakdown products cannot be reused, and are therefore degraded. This gives rise to increased uric acid, a purine breakdown product. This build-up of uric acid is associated with severe gout and kidney problems, poor muscle control and mental retardation, usually in the first year of life. In the second year of life a common sign is self-mutilating behaviors.
Lesch-Nyhan syndrome is an x-linked deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). HGPRT plays a central role in the generation of purine nucleotides through the purine salvage pathway. Cell breakdown products cannot be reused, and are therefore degraded. This gives rise to increased uric acid, a purine breakdown product. This build-up of uric acid is associated with severe gout and kidney problems, poor muscle control and mental retardation, usually in the first year of life. In the second year of life a common sign is self-mutilating behaviors.
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Which of the following classes of enzymes could possibly breakdown collagen, the most common protein in the human body?
Which of the following classes of enzymes could possibly breakdown collagen, the most common protein in the human body?
Because collagen is a protein, it must be broken down by a protease. Proteases exert their effects by hydrolyzing peptide bonds. The specific enzyme that breaks down collagen, predictably, is called collagenase.
The other classes of enzymes listed have actions unrelated to protein breakdown. An isomerase rearranges bonds to form an isomer, a polyermase adds nucleotides to DNA, a lipase breaks down fats, and a ligase creates a chemical bond.
Because collagen is a protein, it must be broken down by a protease. Proteases exert their effects by hydrolyzing peptide bonds. The specific enzyme that breaks down collagen, predictably, is called collagenase.
The other classes of enzymes listed have actions unrelated to protein breakdown. An isomerase rearranges bonds to form an isomer, a polyermase adds nucleotides to DNA, a lipase breaks down fats, and a ligase creates a chemical bond.
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Which of the following describes the role of glutamine synthetase in protein catabolism?
I. Glutamine synthetase converts glutamate and ammonia to glutamine using one molecule of ATP
II. The reaction catalyzed by glutamine synthetase is reversible
III. The reaction catalyzed by glutamine synthetase removes excess nitrogen (in the form of toxic ammonia) from protein degradation
IV. Glutamine synthetase converts glutamine to glutamate
Which of the following describes the role of glutamine synthetase in protein catabolism?
I. Glutamine synthetase converts glutamate and ammonia to glutamine using one molecule of ATP
II. The reaction catalyzed by glutamine synthetase is reversible
III. The reaction catalyzed by glutamine synthetase removes excess nitrogen (in the form of toxic ammonia) from protein degradation
IV. Glutamine synthetase converts glutamine to glutamate
Glutaminase synthetase is present predominately in the brain, liver and kidneys.The importance of the reaction catalyzed by glutamine synthetase is that excess nitrogen (in the form of toxic ammonia) from protein degradation can be removed from tissues, especially the brain. The reaction catalyzed by glutamine synthetase is irreversible. It converts glutamate to glutamine.
Glutaminase synthetase is present predominately in the brain, liver and kidneys.The importance of the reaction catalyzed by glutamine synthetase is that excess nitrogen (in the form of toxic ammonia) from protein degradation can be removed from tissues, especially the brain. The reaction catalyzed by glutamine synthetase is irreversible. It converts glutamate to glutamine.
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Which of these describe(s) the role of aminotransferases in protein catabolism?
I. They are present in the liver and muscle
II. They transfer the amino group from one amino acids to alpha-ketoglutarate
III. In the muscle, these enzymes move the amino group to glutamate, which can be further converted to glutamine which is a excess nitrogen carrier from tissues
IV. They catalyze irreversible reactions and release amino groups as free ammonium
Which of these describe(s) the role of aminotransferases in protein catabolism?
I. They are present in the liver and muscle
II. They transfer the amino group from one amino acids to alpha-ketoglutarate
III. In the muscle, these enzymes move the amino group to glutamate, which can be further converted to glutamine which is a excess nitrogen carrier from tissues
IV. They catalyze irreversible reactions and release amino groups as free ammonium
Aminotransferases do not release amino groups, but rather transfer them to other amino acids. The reactions catalyzed by aminotransferases are reversible. Their blood concentrations can be used as clinical indicators for damage to liver or muscle.
Aminotransferases do not release amino groups, but rather transfer them to other amino acids. The reactions catalyzed by aminotransferases are reversible. Their blood concentrations can be used as clinical indicators for damage to liver or muscle.
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Which of the following regarding mitochondrial carbamoyl phosphate synthetase are true?
I. Mitochondrial carbamoyl phosphate synthetase forms intermediates in the urea cycle
II. Mitochondrial carbamoyl phosphate synthetase utilizes adenosine triphosphate (ATP)
III. A decrease in normal levels of the enzyme leads to a decrease in ammonium ions in the blood
IV. Mitochondrial carbamoyl phosphate synthetase converts ammonium ions to carbamoyl phosphate
Which of the following regarding mitochondrial carbamoyl phosphate synthetase are true?
I. Mitochondrial carbamoyl phosphate synthetase forms intermediates in the urea cycle
II. Mitochondrial carbamoyl phosphate synthetase utilizes adenosine triphosphate (ATP)
III. A decrease in normal levels of the enzyme leads to a decrease in ammonium ions in the blood
IV. Mitochondrial carbamoyl phosphate synthetase converts ammonium ions to carbamoyl phosphate
Mitochondrial carbamoyl phosphate synthetase is important in excretion of ammonium ions as urea. Without it there is an increase in blood ammonium levels (which are toxic to the brain), as well as decreased blood urea levels and increased levels of glutamine (the transporter of ammonium in the blood).
Mitochondrial carbamoyl phosphate synthetase is important in excretion of ammonium ions as urea. Without it there is an increase in blood ammonium levels (which are toxic to the brain), as well as decreased blood urea levels and increased levels of glutamine (the transporter of ammonium in the blood).
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Which of these describe the role of ornithine transcarbamoylase in protein degradation?
I. Ornithine transcarbamoylase converts carbamoyl phosphate to citrulline in the presence of ornithine
II. Ornithine transcarbamoylase is present in the mitochondria
III. Deficiency of the enzyme leads to a decrease of ammonium ions in the blood
IV. Deficiency of the enzyme leads to an increase in urea in the blood
Which of these describe the role of ornithine transcarbamoylase in protein degradation?
I. Ornithine transcarbamoylase converts carbamoyl phosphate to citrulline in the presence of ornithine
II. Ornithine transcarbamoylase is present in the mitochondria
III. Deficiency of the enzyme leads to a decrease of ammonium ions in the blood
IV. Deficiency of the enzyme leads to an increase in urea in the blood
Ornithine transcarbamoylase is part of the urea cycle; it converts carbamoyl phosphate to citrulline in the presence of ornithine. It participates in the pathway that transforms toxic ammonium ions released in amino acid degradation to non-toxic urea that can be eliminated in urine. Ornithine transcarbamoylase is a mitochondrial membrane and its deficiency not only affects urea production, but also leads to accumulation of nucleotide bases such as uracil in the blood and urine. The levels of urea in the blood decrease (not increase) in ornithine transcarbamoylase deficiency.
Ornithine transcarbamoylase is part of the urea cycle; it converts carbamoyl phosphate to citrulline in the presence of ornithine. It participates in the pathway that transforms toxic ammonium ions released in amino acid degradation to non-toxic urea that can be eliminated in urine. Ornithine transcarbamoylase is a mitochondrial membrane and its deficiency not only affects urea production, but also leads to accumulation of nucleotide bases such as uracil in the blood and urine. The levels of urea in the blood decrease (not increase) in ornithine transcarbamoylase deficiency.
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The enzyme responsible for the reaction that produces ammonia during amino acid deamination is .
The enzyme responsible for the reaction that produces ammonia during amino acid deamination is .
The correct answer is "glutamate dehydrogenase." Glutamate is the only amino acid that has an enzyme that removes its amino group as ammonia, rather than just transferring the amino group to a α-keto acid and forming a new amino acid. The transfer of amino groups, which may form glutamate, is performed by aminotransferases that require pyridoxal-5’-phosphate as a cofactor. Cathepsins are a type of proteases contained in lysosomes, and they break down proteins into amino acids rather than metabolize the amino acids themselves. Carbamoyl phosphate synthase is not involved in deamination, but rather condenses ammonia with bicarbonate to enter the urea cycle.
The correct answer is "glutamate dehydrogenase." Glutamate is the only amino acid that has an enzyme that removes its amino group as ammonia, rather than just transferring the amino group to a α-keto acid and forming a new amino acid. The transfer of amino groups, which may form glutamate, is performed by aminotransferases that require pyridoxal-5’-phosphate as a cofactor. Cathepsins are a type of proteases contained in lysosomes, and they break down proteins into amino acids rather than metabolize the amino acids themselves. Carbamoyl phosphate synthase is not involved in deamination, but rather condenses ammonia with bicarbonate to enter the urea cycle.
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The urea cycle is vital to the excretion of ammonia, a harmful byproduct of amino acid breakdown.
What enzyme in the urea cycle converts L-ornithine to L-citrulline?
The urea cycle is vital to the excretion of ammonia, a harmful byproduct of amino acid breakdown.
What enzyme in the urea cycle converts L-ornithine to L-citrulline?
Ornithine transcarbamylase catalyzes the reaction between the substrates ornithine and carbamoyl phosphate to form citrulline and phosphate. This process occurs primarily in the hepatic mitochondria, and to a lesser extent in the mitochondria of the renal cells.
Ornithine transcarbamylase catalyzes the reaction between the substrates ornithine and carbamoyl phosphate to form citrulline and phosphate. This process occurs primarily in the hepatic mitochondria, and to a lesser extent in the mitochondria of the renal cells.
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What enzyme is deficient in Lesch-Nyhan syndrome?
What enzyme is deficient in Lesch-Nyhan syndrome?
Lesch-Nyhan syndrome is an x-linked deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). HGPRT plays a central role in the generation of purine nucleotides through the purine salvage pathway. Cell breakdown products cannot be reused, and are therefore degraded. This gives rise to increased uric acid, a purine breakdown product. This build-up of uric acid is associated with severe gout and kidney problems, poor muscle control and mental retardation, usually in the first year of life. In the second year of life a common sign is self-mutilating behaviors.
Lesch-Nyhan syndrome is an x-linked deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). HGPRT plays a central role in the generation of purine nucleotides through the purine salvage pathway. Cell breakdown products cannot be reused, and are therefore degraded. This gives rise to increased uric acid, a purine breakdown product. This build-up of uric acid is associated with severe gout and kidney problems, poor muscle control and mental retardation, usually in the first year of life. In the second year of life a common sign is self-mutilating behaviors.
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Which of the following classes of enzymes could possibly breakdown collagen, the most common protein in the human body?
Which of the following classes of enzymes could possibly breakdown collagen, the most common protein in the human body?
Because collagen is a protein, it must be broken down by a protease. Proteases exert their effects by hydrolyzing peptide bonds. The specific enzyme that breaks down collagen, predictably, is called collagenase.
The other classes of enzymes listed have actions unrelated to protein breakdown. An isomerase rearranges bonds to form an isomer, a polyermase adds nucleotides to DNA, a lipase breaks down fats, and a ligase creates a chemical bond.
Because collagen is a protein, it must be broken down by a protease. Proteases exert their effects by hydrolyzing peptide bonds. The specific enzyme that breaks down collagen, predictably, is called collagenase.
The other classes of enzymes listed have actions unrelated to protein breakdown. An isomerase rearranges bonds to form an isomer, a polyermase adds nucleotides to DNA, a lipase breaks down fats, and a ligase creates a chemical bond.
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