Harper's Biochemistry Chapter 29 - Catabolism of the Carbon Skeletons of Amino Acids
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Questions and Answers

What is the primary role of CH3 in the context of active methionine?

  • To enhance protein synthesis rates
  • To act as a cofactor in enzyme reactions
  • To signify the high group transfer potential (correct)
  • To facilitate amino acid deamination

    • Which amino acids share a similar catabolic pathway with fatty acids?

  • Methionine and Cysteine
  • Leucine and Valine (correct)
  • Isoleucine and Tryptophan
  • Phenylalanine and Tyrosine

    • Which of the following best describes Maple Syrup Urine Disease?

  • A disorder linked to increased methionine levels
  • Impaired function of components of the α-ketoacid decarboxylase complex (correct)
  • A metabolic syndrome affecting protein digestion
  • A condition caused by excess valine only

    • Which component is NOT part of the α-Ketoacid Decarboxylase Complex?

    <p>E4 – Transaminase</p> Signup and view all the answers

    What is the end product of l-leucine catabolism?

    <p>β-methylcrotonyl-CoA</p> Signup and view all the answers

    Which analogy is made between amino acid and fatty acid catabolism?

    <p>The breaking down process of carbon skeletons</p> Signup and view all the answers

    Which of these branched-chain amino acids is associated with type I maple syrup urine disease?

    <p>Leucine</p> Signup and view all the answers

    Which enzyme class is NOT involved in the catabolism of branched-chain amino acids?

    <p>Lactate dehydrogenase</p> Signup and view all the answers

    What could result from mutations affecting enzyme activity during amino acid catabolism?

    <p>Impaired enzyme activity and potential metabolic disorders</p> Signup and view all the answers

    Which of the following processes is NOT a consequence of mutations in amino acid metabolism?

    <p>Increased production of substrates</p> Signup and view all the answers

    How can prenatal diagnosis facilitate the management of metabolic disorders related to amino acids?

    <p>Through the detection of enzyme activities in amniotic fluid</p> Signup and view all the answers

    Which statement best describes the role of allosteric regulators in amino acid metabolism?

    <p>They can impair the ability of certain enzymes to respond appropriately.</p> Signup and view all the answers

    What characteristic of metabolic disorders associated with amino acid catabolism may lead to similar symptoms despite different mutations?

    <p>Different mutations can impact the same biochemical pathways</p> Signup and view all the answers

    What is the primary catabolite produced from the breakdown of proline?

    <p>Glutamate</p> Signup and view all the answers

    Which coenzyme is critical for aminotransferase reactions?

    <p>Pyridoxal phosphate</p> Signup and view all the answers

    In which metabolic disorder is there an accumulation of branched-chain amino acids?

    <p>Maple syrup urine disease</p> Signup and view all the answers

    Which process is responsible for the removal of α-amino nitrogen from lysine aside from transamination?

    <p>Deamination</p> Signup and view all the answers

    Which of the following represents an analogy between the catabolism of amino acids and fatty acids?

    <p>Both can generate acyl-CoA derivatives.</p> Signup and view all the answers

    What is a consequence of impaired intestinal absorption of tryptophan?

    <p>Serotonin deficiency</p> Signup and view all the answers

    Which condition is characterized by a defect in the metabolism of methylmalonic acid?

    <p>Methylmalonic aciduria</p> Signup and view all the answers

    Which enzyme's defect leads to hypervalinemia?

    <p>Branched-chain alpha-keto acid dehydrogenase</p> Signup and view all the answers

    What role does S-adenosylmethionine play in amino acid metabolism?

    <p>It acts as a methyl donor in various methylation reactions.</p> Signup and view all the answers

    Which type of screening tests are most reliable for detecting metabolic defects in amino acids?

    <p>Tandem mass spectrometry</p> Signup and view all the answers

    What is formed when methionine reacts with ATP?

    <p>S-adenosylmethionine</p> Signup and view all the answers

    Which compound is a product of kynureninase activity?

    <p>Xanthurenate</p> Signup and view all the answers

    What best describes the role of branched-chain alpha-ketoacid dehydrogenase complex?

    <p>Catalyzes the multistep process involving branched-chain amino acids</p> Signup and view all the answers

    Which characteristic is common between the metabolic pathways of branched-chain amino acids and fatty acids?

    <p>Both are primarily associated with mitochondrial function.</p> Signup and view all the answers

    Hartnup disease primarily affects the transport of which type of amino acids?

    <p>Neutral amino acids</p> Signup and view all the answers

    What is a major diagnostic indicator of vitamin B6 deficiency?

    <p>Excretion of xanthurenate</p> Signup and view all the answers

    Which component is involved in the branched-chain alpha-ketoacid dehydrogenase complex?

    <p>Thiamin pyrophosphate</p> Signup and view all the answers

    Which of the following best explains the catabolic fate of propionyl-CoA?

    <p>It is converted to succinyl-CoA through a series of reactions.</p> Signup and view all the answers

    What is the enzyme classification of kynurenine formylase?

    <p>EC 3.5.1.9</p> Signup and view all the answers

    What is the main consequence of impaired intestinal transport of tryptophan?

    <p>Decreased availability of niacin</p> Signup and view all the answers

    Which of the following metabolic defects is associated with type-II hyperprolinemia?

    <p>Impaired conversion of l-arginine to urea</p> Signup and view all the answers

    What is the primary product of the glycine cleavage system in liver mitochondria?

    <p>CO2 and NH4+</p> Signup and view all the answers

    What role does tetrahydrofolate play in the metabolism of amino acids?

    <p>It transfers the formimino group to form glutamate.</p> Signup and view all the answers

    Which disorder is related to impaired histidine metabolism?

    <p>Histidinemia</p> Signup and view all the answers

    How does the glycine cleavage complex contribute to amino acid catabolism?

    <p>It cleaves glycine into CO2, NH4+, and a methylene derivative.</p> Signup and view all the answers

    What is the significance of the red bars and circles in the metabolic pathway diagram?

    <p>They represent points of inherited metabolic defects.</p> Signup and view all the answers

    Which of the following reactions is part of the subsequent metabolic steps following glycine cleavage?

    <p>Conversion of glutamate to α-ketoglutarate.</p> Signup and view all the answers

    What metabolic process is shared between amino acids and fatty acids?

    <p>Deamination</p> Signup and view all the answers

    What byproduct is produced from the incomplete metabolism of histidine?

    <p>Urocanic acid</p> Signup and view all the answers

    Which amino acid catabolism step involves oxidation to form an intermediate critical for nitrogen metabolism?

    <p>Oxidation of glutamate-γ-semialdehyde</p> Signup and view all the answers

    What are the consequences of untreated metabolic disorders related to amino acid metabolism?

    <p>Irreversible brain damage and early mortality</p> Signup and view all the answers

    Which of the following best describes the role of mutations in enzyme efficiency within metabolic disorders?

    <p>Mutations can reduce the positioning of residues that affect catalytic action</p> Signup and view all the answers

    What type of diagnostic procedure can help identify metabolic disorders in prenatal stages?

    <p>Amniocentesis</p> Signup and view all the answers

    What is the primary pathogenic effect observed in molecular diseases due to different mutations affecting metabolic pathways?

    <p>Diverse clinical presentations with similar symptoms</p> Signup and view all the answers

    What critical aspect of enzyme activity can be impaired due to specific mutations affecting regulatory sites?

    <p>Enzyme affinity for allosteric regulators</p> Signup and view all the answers

    What is a common characteristic of metabolic disorders associated with amino acid metabolism?

    <p>They often stem from enzymatic deficiencies</p> Signup and view all the answers

    Which of the following best describes the impact of low catalytic efficiency in mutant enzymes?

    <p>Impaired positioning of residues crucial for catalytic function</p> Signup and view all the answers

    Which amino acids are primarily involved in the formation of oxaloacetate?

    <p>Asparagine and Aspartate</p> Signup and view all the answers

    What is suggested as a potential permanent solution for metabolic disorders related to amino acid metabolism?

    <p>Gene therapy</p> Signup and view all the answers

    What did studies conducted between 1920 to 1940 primarily confirm about amino acids?

    <p>Amino acids can serve as precursors for both carbohydrates and lipids.</p> Signup and view all the answers

    Which amino acids are classified as ketogenic?

    <p>Leucine and Lysine</p> Signup and view all the answers

    Which enzymatic reaction is responsible for the conversion of asparagine into oxaloacetate?

    <p>Transamination</p> Signup and view all the answers

    What major conclusion did isotopic studies reveal about metabolic pathways involving amino acids?

    <p>Carbon skeletons of amino acids can integrate into various metabolic pathways.</p> Signup and view all the answers

    Which amino acid's carbon skeleton is significant for both lipid and carbohydrate biosynthesis?

    <p>Arginine</p> Signup and view all the answers

    Which carbon-containing compounds do the studies suggest that specific amino acids can be converted into?

    <p>Both carbohydrates and fatty acids</p> Signup and view all the answers

    What type of dietary intervention is typically employed for metabolic disorders related to impaired amino acid metabolism?

    <p>Feeding diets low in specific amino acids</p> Signup and view all the answers

    What is the primary consequence of early diagnosis in metabolic disorders related to amino acids?

    <p>Reduction of neurological damage</p> Signup and view all the answers

    Which enzyme defect is directly associated with isovaleric acidemia?

    <p>Isovaleryl-CoA dehydrogenase</p> Signup and view all the answers

    Which statement best describes the molecular genetics of Maple Syrup Urine Disease (MSUD)?

    <p>It can result from mutations in any of the four genes coding for E1α, E1β, E2, or E3.</p> Signup and view all the answers

    Which of the following substances is primarily elevated due to the metabolic defect in isovaleric acidemia?

    <p>Isovalerylcarnitine</p> Signup and view all the answers

    What is the role of dietary protein in the context of avoiding early mortality in metabolic disorders?

    <p>It must be replaced with an amino acid mixture.</p> Signup and view all the answers

    Which amino acids do not participate in transamination?

    <p>Proline</p> Signup and view all the answers

    What is produced from the reaction of glutamine and water?

    <p>Glutamate and ammonium</p> Signup and view all the answers

    Which metabolic defect is associated with a specific enzyme in type I hyperprolinemia?

    <p>Proline dehydrogenase</p> Signup and view all the answers

    What happens to the remaining carbon skeleton after transamination?

    <p>It forms glucogenic intermediates.</p> Signup and view all the answers

    Which of the following amino acids can provide α-ketoglutarate through transamination?

    <p>Aspartate</p> Signup and view all the answers

    Which metabolites are formed from the breakdown of asparagine and glutamine?

    <p>Aspartate and α-ketoglutarate</p> Signup and view all the answers

    What distinguishes the catabolism of proline from other amino acids?

    <p>It involves mitochondrial reactions.</p> Signup and view all the answers

    Which enzyme class is directly involved in the transamination reactions associated with amino acid catabolism?

    <p>Transaminases</p> Signup and view all the answers

    Which of the following reactions accurately represents a step in the metabolism of glutamate?

    <p>Glutamate + α-Ketoglutarate → Aspartate + Glutamine</p> Signup and view all the answers

    What defines the amphibolic intermediates produced during amino acid catabolism?

    <p>They are utilized in both catabolic and anabolic pathways.</p> Signup and view all the answers

    What is the primary defect observed in nonketotic hyperglycinemia?

    <p>Accumulation of glycine in tissues</p> Signup and view all the answers

    Which condition is primarily caused by the failure to metabolize glyoxylic acid?

    <p>Primary hyperoxaluria</p> Signup and view all the answers

    Which enzyme is critical in the catabolism of glycine following its conversion from serine?

    <p>Glycine hydroxymethyltransferase</p> Signup and view all the answers

    What is one of the major consequences of glycinuria?

    <p>Decreased reabsorption of glycine in the renal tubules</p> Signup and view all the answers

    What primary process leads to the formation of oxalate from glyoxylic acid?

    <p>Oxidation of glyoxylic acid</p> Signup and view all the answers

    Which of the following describes the role of the glycine cleavage complex?

    <p>Cleavage of glycine to produce ammonia and carbon dioxide</p> Signup and view all the answers

    What is a potential outcome of renal failure caused by the accumulation of oxalate?

    <p>Development of urolithiasis</p> Signup and view all the answers

    In the context of serine metabolism, what role does glycine hydroxymethyltransferase serve?

    <p>It facilitates the conversion of serine to glycine</p> Signup and view all the answers

    What is the implication of inherited defects in the glycine cleavage system?

    <p>Potentially toxic accumulation of glycine</p> Signup and view all the answers

    Match the following amino acids with their associated metabolic pathways:

    <p>Tyrosine = Fumarate and Acetoacetate Lysine = Saccharopine pathway Phenylalanine = Phenylpyruvate formation Leucine = Acetoacetate formation</p> Signup and view all the answers

    Match the following metabolic disorders with their corresponding enzyme deficiencies:

    <p>Type I Tyrosinemia = Fumarylacetoacetate hydrolase Maple Syrup Urine Disease = Branched-chain alpha-ketoacid dehydrogenase Phenylketonuria (PKU) = Phenylalanine hydroxylase Tyrosinemia type II = Tyrosine aminotransferase</p> Signup and view all the answers

    Match the following compounds with their respective roles in amino acid metabolism:

    <p>Acetyl-CoA = Energy production Aminoadipate-δ-semialdehyde = Lysine catabolism Kynurenine = Tryptophan degradation Homogentisate = Tyrosine metabolism</p> Signup and view all the answers

    Match the following enzymes with the amino acid they primarily metabolize:

    <p>Amino acid decarboxylase = Amino acids to amines Phenylalanine hydroxylase = Phenylalanine to Tyrosine Aminotransferase = Amino acid to α-ketoacid Fumarylacetoacetate hydrolase = Tyrosine to fumarate</p> Signup and view all the answers

    Match the following metabolic intermediates with their sources:

    <p>p-hydroxyphenylpyruvate = Tyrosine transamination Fumarate = Tyrosine degradation Acetoacetate = Leucine metabolism Alpha-ketoglutarate = Glutamate deamination</p> Signup and view all the answers

    Match the following amino acids with their primary metabolic pathways or functions:

    <p>Phenylalanine = Converted to tyrosine Tryptophan = Degraded via kynurenine-anthranilate pathway Lysine = Restrict dietary intake in phenylketonuria Tyrosine = Intermediates in catabolism pathways</p> Signup and view all the answers

    Match the following enzymes with their related metabolic processes:

    <p>Phenylalanine hydroxyloase = Defect leads to phenylketonuria Dihydropterin reductase = Involved in tyrosine metabolism Tryptophan oxygenase = Catalyzes conversion of tryptophan Kynurenine formylase = Converts kynurenine into metabolic byproducts</p> Signup and view all the answers

    Match the following conditions with their characteristics:

    <p>Classic phenylketonuria = Arises from defects in phenylalanine metabolism Type II hyperprolinemia = Involves defective proline metabolism Neonatal tyrosinemia = Results from tyrosine metabolism defects Alkaptonuria = Involves accumulation of homogentisic acid</p> Signup and view all the answers

    Match the following products with their source amino acids:

    <p>N-formylkynurenine = Formed from tryptophan degradation Tyrosine = Derived from phenylalanine Amphibolic intermediates = Produced from tryptophan catabolism Glutamate = Can be produced from multiple amino acids</p> Signup and view all the answers

    Match the following metabolic features with their specific amino acid:

    <p>Tryptophan = Forms part of serotonin synthesis Phenylalanine = Requires dietary control to prevent accumulation Lysine = High dietary intake leads to probing metabolism Tyrosine = Serves as a precursor for neurotransmitters</p> Signup and view all the answers

    Study Notes

    Catabolism of Amino Acid Carbon Skeletons

    • Amino acid catabolism involves the breakdown of amino acid carbon skeletons into metabolic intermediates
    • The nitrogen atoms are removed typically through transamination
    • Key catabolites include oxaloacetate, a-ketoglutarate, pyruvate, and acetyl-CoA
    • Many metabolic disorders are related to defects in specific enzymes during amino acid catabolism
    • These defects often lead to similar clinical symptoms

    Biomedical Importance

    • Amino acid catabolism disorders are relatively rare but can lead to severe brain damage and early mortality without treatment
    • Early detection and intervention are crucial, and newborn screening programs are implemented to identify such disorders early on
    • Tandem mass spectrometry is a reliable screening method used to detect metabolic defects
    • Feeding diets low in the affected amino acid is an often used remediation method
    • Genetic engineering may eventually offer treatment options for these severe metabolic disorders

    Amino Acid Catabolism to Carbohydrates and Lipids

    • The carbon atoms of amino acids can be converted into carbohydrate and fat
    • Table 29-1 details the fate of amino acid carbon skeletons

    Transamination Initiates Amino Acid Catabolism

    • Transamination reactions, catalyzed by transaminases, are the initial steps for most amino acid catabolism
    • Proline, hydroxyproline, threonine, and lysine are notable exceptions, as their a-amino groups do not participate in transamination reactions

    Proline Breakdown

    • Proline is broken down in mitochondria
    • Proline dehydrogenase converts proline to A¹-pyrroline-5-carboxylate
    • A¹-pyrroline-5-carboxylate dehydrogenase converts A¹-pyrroline-5-carboxylate to glutamate

    Arginine and Ornithine Breakdown

    • Arginine is converted to ornithine and then to glutamate-y-semialdehyde
    • Mutations in ornithine transaminase lead to hyperornithinemia-hyperammonemia syndrome, a condition that affects the transport of ornithine into mitochondria.

    Histidine Breakdown

    • Histidine catabolism proceeds via urocanate, 4-imidazolone-5-propionate, and N-formiminoglutamate
    • Folic acid deficiency can lead to Figlu excretion in the urine

    Glycine, Serine, Alanine, Cysteine, Threonine Breakdown

    • Glycine catabolism converts glycine to CO2, NH3 and N5,N10-methylene tetrahydrofolate
    • Serine catabolism merges with glycine catabolism after conversion to glycine
    • Alanine catabolism results in pyruvate
    • Cysteine catabolism proceeds via two pathways forming pyruvate, sulfate
    • Threonine catabolism forms glycine and acetaldehyde, then acetyl-CoA and acetate

    4-Hydroxyproline Breakdown

    • 4-hydroxyproline catabolism produces multiple intermediates ending with glyoxylate and pyruvate

    Tyrosine Breakdown

    • Tyrosine catabolism forms intermediates like p-hydroxyphenylpyruvate, homogentisate
    • Defects in specific enzymes within tyrosine catabolism lead to various medical conditions such as tyrosinemia or alkaptonuria

    Phenylalanine Breakdown

    • Phenylalanine is converted to tyrosine
    • Defects in phenylalanine hydroxylase lead to phenylketonuria

    Lysine Breakdown

    • Lysine's ε-nitrogen is removed via saccharopine formation, releasing α-nitrogen and ultimately generating crotonyl-CoA

    Tryptophan Breakdown

    • Tryptophan is broken down via the kynurenine-anthranilate pathway
    • The pathway involves tryptophan 2,3-dioxygenase, and produces N-formylkynurenine

    Branched-Chain Amino Acid Catabolism

    • Branched-chain amino acids (BCAAs) follow similar initial steps, resulting in a-keto acid equivalents
    • An a-ketoacid decarboxylase complex is crucial
    • Deficiencies in this complex or associated enzymes like isovaleryl-CoA dehydrogenase can lead to various conditions like maple syrup urine disease, isovaleric acidemia, and methylmalonic aciduria

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    Harper's Biochemistry: Chapter 29 - Catabolism of Amino Acids PDF

    Description

    This quiz covers the catabolism of amino acid carbon skeletons, focusing on key catabolites and the role of nitrogen removal through transamination. It also explores the biomedical importance of amino acid catabolism disorders, including detection methods and potential treatments.

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