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Questions and Answers
Which amino acid is formed directly from α-ketoisovalerate?
Which amino acid is formed directly from α-ketoisovalerate?
Proline is synthesized from glutamate through a two-step pathway.
Proline is synthesized from glutamate through a two-step pathway.
False
What is the name of the coenzyme that is involved in the reduction of the glutamate 5-semialdehyde intermediate to produce proline?
What is the name of the coenzyme that is involved in the reduction of the glutamate 5-semialdehyde intermediate to produce proline?
pyridine nucleotide
Serine is a major source of ______ via a reversible reaction.
Serine is a major source of ______ via a reversible reaction.
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Match the following amino acids with their synthesis precursors:
Match the following amino acids with their synthesis precursors:
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Which amino acids can be synthesized from aspartate?
Which amino acids can be synthesized from aspartate?
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Aspartate is phosphorylated by aspartate kinase in animal cells.
Aspartate is phosphorylated by aspartate kinase in animal cells.
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What is the second step in the biosynthetic pathway involving aspartate?
What is the second step in the biosynthetic pathway involving aspartate?
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The first step in the synthesis of lysine, methionine, and threonine from aspartate involves the phosphorylation of _____ .
The first step in the synthesis of lysine, methionine, and threonine from aspartate involves the phosphorylation of _____ .
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Match the following enzymes with their functions:
Match the following enzymes with their functions:
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Which organisms have the enzymes needed for aspartate metabolism?
Which organisms have the enzymes needed for aspartate metabolism?
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Aspartate is directly converted to lysine.
Aspartate is directly converted to lysine.
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Name one amino acid that cannot be synthesized by animals from aspartate.
Name one amino acid that cannot be synthesized by animals from aspartate.
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Which amino acids are formed from homoserine?
Which amino acids are formed from homoserine?
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Methionine is classified as a non-essential amino acid.
Methionine is classified as a non-essential amino acid.
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Name the enzyme that catalyzes the conversion of homocysteine to methionine.
Name the enzyme that catalyzes the conversion of homocysteine to methionine.
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The sulfur atom of homocysteine accepts a methyl group derived from ______ to form methionine.
The sulfur atom of homocysteine accepts a methyl group derived from ______ to form methionine.
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Match the following amino acids with their essentiality status:
Match the following amino acids with their essentiality status:
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Which vitamin is required by homocysteine methyltransferase?
Which vitamin is required by homocysteine methyltransferase?
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All three amino acids methionine, lysine, and threonine can be synthesized from homoserine.
All three amino acids methionine, lysine, and threonine can be synthesized from homoserine.
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From which amino acid do cysteine and tyrosine derive their precursors?
From which amino acid do cysteine and tyrosine derive their precursors?
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Homocysteine is converted to homocysteine in ______ steps.
Homocysteine is converted to homocysteine in ______ steps.
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Match the following amino acids with their metabolic pathways:
Match the following amino acids with their metabolic pathways:
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What is the primary role of oxaloacetate in the synthesis of aspartate?
What is the primary role of oxaloacetate in the synthesis of aspartate?
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Aspartate is synthesized by transferring the amide nitrogen of glutamine to pyruvate.
Aspartate is synthesized by transferring the amide nitrogen of glutamine to pyruvate.
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Which enzyme catalyzes the reaction that produces aspartate?
Which enzyme catalyzes the reaction that produces aspartate?
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Asparagine is synthesized in most species by an ATP-dependent transfer of the amide nitrogen of _____ to aspartate.
Asparagine is synthesized in most species by an ATP-dependent transfer of the amide nitrogen of _____ to aspartate.
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Which amino acid is synthesized using pyruvate as the amino group acceptor?
Which amino acid is synthesized using pyruvate as the amino group acceptor?
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Branched chain amino acids are synthesized from threonine through a direct conversion to pyruvate.
Branched chain amino acids are synthesized from threonine through a direct conversion to pyruvate.
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List the branched chain amino acids mentioned in the content.
List the branched chain amino acids mentioned in the content.
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The first step in the branched chain pathway is the synthesis of α-keto________ from threonine.
The first step in the branched chain pathway is the synthesis of α-keto________ from threonine.
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Match each amino acid to its precursor:
Match each amino acid to its precursor:
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What enhances the synthesis of asparagine in the body?
What enhances the synthesis of asparagine in the body?
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Study Notes
Biosynthesis of Amino Acids
- The biosynthesis of amino acids is connected to glycolysis/gluconeogenesis and the citric acid cycle.
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Aspartate and Asparagine are synthesized from oxaloacetate, a citric acid cycle intermediate.
- Aspartate is formed via a transamination reaction with glutamate, catalyzed by aspartate transaminase.
- Asparagine is synthesized through the transfer of the amide nitrogen of glutamine to aspartate, catalyzed by asparagine synthetase.
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Lysine, Methionine, and Threonine are derived from aspartate.
- The first step in their synthesis is the phosphorylation of aspartate by aspartate kinase.
- Aspartyl phosphate is then converted to aspartate β-semialdehyde by aspartate semialdehyde dehydrogenase.
- These two enzymes are absent in animals.
- Homoserine, derived from aspartate β-semialdehyde, is a branch point for the formation of threonine and methionine.
- Threonine is produced from homoserine in two steps, one needing pyridoxal phosphate (PLP).
- The conversion of homoserine to homocysteine involves three steps in the methionine pathway.
- The sulfur atom of homocysteine receives a methyl group from 5-methyl-THF, forming methionine.
- This reaction is catalyzed by homocysteine methyltransferase, requiring cobalamin.
- While homocysteine methyltransferase is present in mammals, its activity is low, making methionine an essential amino acid.
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Alanine, Valine, Leucine, and Isoleucine are synthesized from pyruvate.
- Alanine is produced via a transamination reaction between pyruvate and glutamate.
- Valine, leucine, and isoleucine synthesis involves the branched chain pathway starting with α-ketobutyrate from threonine.
- Pyruvate combines with α-ketobutyrate in three steps to form α-keto-β-methylvalerate, which is converted to isoleucine through transamination.
- The same enzyme responsible for α-keto-β-methylvalerate synthesis also catalyzes the synthesis of α-ketoisovalerate from two pyruvate molecules.
- α-ketoisovalerate is directly converted to valine by valine transaminase.
- α-ketoisovalerate is converted to leucine through four reactions.
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Glutamate, Glutamine, Arginine, and Proline are synthesized from α-ketoglutarate, a citric acid cycle intermediate.
- Glutamate and glutamine production has been previously discussed.
- Proline and arginine also utilize α-ketoglutarate, passing through glutamate.
- Proline synthesis from glutamate involves four steps, reducing the 5-carboxylate group of glutamate to an aldehyde.
- The intermediate, glutamate 5-semialdehyde, undergoes non-enzymatic cyclization to a Schiff's base, reduced by a pyridine nucleotide coenzyme to form proline.
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Serine, Glycine, and Cysteine are derived from 3-phosphoglycerate, a glycolysis/gluconeogenesis intermediate.
- 3-phosphoglycerate is oxidized to 3-phosphohydroxypyruvate, which undergoes transamination with glutamate to form 3-phosphoserine and α-ketoglutarate.
- 3-phosphoserine is hydrolyzed to serine and Pi.
- Serine is the primary source of glycine through a reversible reaction catalyzed by serine hydroxymethyltransferase.
- Cysteine synthesis from serine in bacteria and plants occurs in two steps.
- Serine's β-hydroxyl substituent is acetylated by acetyl CoA, forming O-acetylserine.
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Methionine and phenylalanine are precursors for cysteine and tyrosine, respectively.
- These latter amino acids can become essential if adequate amounts of their precursors are not supplied in the diet.
- Arginine is a conditionally essential amino acid, meaning the body synthesizes it but not enough to meet needs during growth.
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Description
Explore the intricate pathways involved in the biosynthesis of amino acids such as aspartate, asparagine, lysine, methionine, and threonine. This quiz delves into how these amino acids are synthesized from glycolysis and the citric acid cycle, highlighting key reactions and enzymes. Test your understanding of this essential biochemical process.
