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Questions and Answers
Which nonessential amino acid is synthesized from pyruvate?
Which nonessential amino acid is synthesized from pyruvate?
What role does homocysteine play in relation to diseases?
What role does homocysteine play in relation to diseases?
Which amino acid is synthesized from 3-phosphoglycerate?
Which amino acid is synthesized from 3-phosphoglycerate?
What process is used to synthesize glutamine from glutamate?
What process is used to synthesize glutamine from glutamate?
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Which pair represents an amino acid synthesized from an essential amino acid?
Which pair represents an amino acid synthesized from an essential amino acid?
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Which amino acid synthesis involves ATP consumption?
Which amino acid synthesis involves ATP consumption?
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What is the primary source for synthesizing glycine from serine?
What is the primary source for synthesizing glycine from serine?
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What amino acid is synthesized by transamination from oxaloacetate?
What amino acid is synthesized by transamination from oxaloacetate?
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Which compound is synthesized when homocysteine combines with serine?
Which compound is synthesized when homocysteine combines with serine?
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What essential amino acid is required for the synthesis of cysteine?
What essential amino acid is required for the synthesis of cysteine?
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What is the primary role of S-adenosylmethionine (SAM) in one carbon metabolism?
What is the primary role of S-adenosylmethionine (SAM) in one carbon metabolism?
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What happens to homocysteine if there is a deficiency of methionine?
What happens to homocysteine if there is a deficiency of methionine?
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Which amino acid is directly derived from phenylalanine?
Which amino acid is directly derived from phenylalanine?
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What coenzyme is required for the conversion of homocysteine to methionine?
What coenzyme is required for the conversion of homocysteine to methionine?
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What does an elevation in plasma homocysteine levels indicate in relation to vascular health?
What does an elevation in plasma homocysteine levels indicate in relation to vascular health?
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What is the fate of S-adenosylhomocysteine after donating its methyl group?
What is the fate of S-adenosylhomocysteine after donating its methyl group?
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Study Notes
Clinical Biochemistry Lecture 4: Amino Acid Synthesis
- Lecture: 4, Topic: Synthesis of amino acids, Year: 2024, Stage: Second Stage, Professor: Dr. Thana Mohammed, Email: [email protected]
Objectives
- Objective 1: Describe the main pathway of amino acid synthesis.
- Objective 2: Identify cofactors crucial for amino acid synthesis.
- Objective 3: Explain the role of folic acid in glycine and serine metabolism.
- Objective 4: Explain the role of homocysteine as a risk factor in disease.
Biosynthesis of Nonessential Amino Acids
- Nonessential amino acids are produced from metabolic intermediates or essential amino acids.
- The 10 amino acids that can be synthesized are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
- Some, like tyrosine and cysteine, are synthesized from essential amino acids phenylalanine and methionine, respectively.
Synthesis of Amino Acids from α-Keto Acids
- Alanine, aspartate, and glutamate are synthesized by transferring an amino group to α-keto acids like pyruvate, oxaloacetate, and α-ketoglutarate.
- These transamination reactions are direct biosynthetic pathways.
- Glutamate is unique, as it can also be synthesized through the reverse of oxidative deamination, catalyzed by glutamate dehydrogenase.
Synthesis by Amination
- Glutamine: Formed from glutamate by glutamine synthetase, involving an amide linkage with ammonia at the γ-carboxyl. Requires ATP.
- Asparagine: Formedi from aspartate, involving an amide linkage with ammonia at the β-carboxyl. Driven by asparagine synthetase using glutamine as a donor. Requires ATP.
Serine, Glycine, and Cysteine Synthesis
- Serine: Synthesized from 3-phosphoglycerate (an intermediate in glycolysis), oxidized to phosphopyruvate, then transaminated to 3-phosphoserine. Subsequently, hydrolyzed to serine.
- Serine can also form from glycine through the transfer of a hydroxymethyl group.
- Glycine: Synthesized from serine by removal of a methyl group by serine hydroxymethyl transferase. Tetrahydrofolate (THF) serves as a one-carbon acceptor.
- Cysteine: Synthesized from serine through two consecutive reactions. Homocysteine combines with serine, forming cystathionine, which is hydrolyzed to α-ketobutyrate and cysteine. Methionine is an essential amino acid; cysteine synthesis depends on adequate methionine intake.
Homocysteine Metabolism
- Homocysteine is derived from methionine.
- Adequate methionine intake is necessary for sustaining cysteine synthesis.
- Homocysteine has two possible fates: remethylation to methionine or entry into the transsulfuration pathway to form cysteine.
- Elevated homocysteine levels are linked to oxidative damage, inflammation, and endothelial dysfunction, raising the risk for occlusive vascular diseases. Vitamin B12, B6, and folic acid are important in homocysteine metabolism.
Tyrosine Synthesis
- Tyrosine is formed from phenylalanine through the action of phenylalanine hydroxylase.
- The reaction requires molecular oxygen and the coenzyme tetrahydrobiopterin.
- Tyrosine is a nonessential amino acid but depends on a sufficient supply of the essential amino acids phenylalanine and methionine.
High Methionine and Phenylalanine Foods
- High levels of methionine (nuts) and phenylalanine (beans) are needed for cysteine and tyrosine synthesis respectively when adequate amounts are not supplied through the diet.
Synthesis of S-Adenosylmethionine
- Methionine combines with ATP to form S-adenosylmethionine (SAM). SAM is a high-energy compound crucial as a major methyl group donor in one carbon metabolism.
- After the donation of a methyl group, SAM is converted to S-adenosylhomocysteine, which is then hydrolyzed to homocysteine and adenosine.
Coenzyme in Amino Acid Metabolism
- Vitamins (e.g., B6, B12, and folate) and other molecules like tetrahydrobiopterin act as important coenzymes supporting various amino acid metabolic reactions (e.g., transamination, hydroxylase activities, and methyl group transfer), which are a critical part of glycine-serine interconversion, homocysteine to methionine synthesis, etc).
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Description
Explore the pathways of amino acid synthesis in this comprehensive quiz based on Clinical Biochemistry Lecture 4. Learn about the crucial cofactors, the role of folic acid in metabolism, and the significance of homocysteine in disease risk. Test your knowledge on nonessential amino acids and their biosynthesis.
