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 (A)</p> Signup and view all the answers

What is the end product of l-leucine catabolism?

<p>β-methylcrotonyl-CoA (B)</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 (B)</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 (D)</p> Signup and view all the answers

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

<p>Lactate dehydrogenase (B)</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 (A)</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 (D)</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 (B)</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. (D)</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 (D)</p> Signup and view all the answers

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

<p>Glutamate (A)</p> Signup and view all the answers

Which coenzyme is critical for aminotransferase reactions?

<p>Pyridoxal phosphate (A)</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 (C)</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 (B)</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. (C)</p> Signup and view all the answers

What is a consequence of impaired intestinal absorption of tryptophan?

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

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

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

Which enzyme's defect leads to hypervalinemia?

<p>Branched-chain alpha-keto acid dehydrogenase (B)</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. (A)</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 (C)</p> Signup and view all the answers

What is formed when methionine reacts with ATP?

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

Which compound is a product of kynureninase activity?

<p>Xanthurenate (C)</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 (D)</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. (B)</p> Signup and view all the answers

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

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

What is a major diagnostic indicator of vitamin B6 deficiency?

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

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

<p>Thiamin pyrophosphate (B)</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. (A)</p> Signup and view all the answers

What is the enzyme classification of kynurenine formylase?

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

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

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

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

<p>CO2 and NH4+ (B)</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. (D)</p> Signup and view all the answers

Which disorder is related to impaired histidine metabolism?

<p>Histidinemia (C)</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. (D)</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. (C)</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. (D)</p> Signup and view all the answers

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

<p>Deamination (A)</p> Signup and view all the answers

What byproduct is produced from the incomplete metabolism of histidine?

<p>Urocanic acid (D)</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 (C)</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 (D)</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 (D)</p> Signup and view all the answers

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

<p>Amniocentesis (D)</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 (A)</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 (A)</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 (D)</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 (B)</p> Signup and view all the answers

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

<p>Asparagine and Aspartate (D)</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 (C)</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. (C)</p> Signup and view all the answers

Which amino acids are classified as ketogenic?

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

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

<p>Transamination (B)</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. (B)</p> Signup and view all the answers

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

<p>Arginine (B)</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 (A)</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 (B)</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 (C)</p> Signup and view all the answers

Which enzyme defect is directly associated with isovaleric acidemia?

<p>Isovaleryl-CoA dehydrogenase (A)</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. (B)</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 (C)</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. (D)</p> Signup and view all the answers

Which amino acids do not participate in transamination?

<p>Proline (A), Threonine (C)</p> Signup and view all the answers

What is produced from the reaction of glutamine and water?

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

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

<p>Proline dehydrogenase (A), Proline dehydrogenase (B)</p> Signup and view all the answers

What happens to the remaining carbon skeleton after transamination?

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

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

<p>Aspartate (A)</p> Signup and view all the answers

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

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

What distinguishes the catabolism of proline from other amino acids?

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

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

<p>Transaminases (C)</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 (B)</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. (C)</p> Signup and view all the answers

What is the primary defect observed in nonketotic hyperglycinemia?

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

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

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

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

<p>Glycine hydroxymethyltransferase (A)</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 (C)</p> Signup and view all the answers

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

<p>Oxidation of glyoxylic acid (C)</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 (B)</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 (A)</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 (A)</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 (C)</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

Flashcards

Methionine Catabolism

The breakdown of methionine into propionyl-CoA.

Leucine, Valine, Isoleucine Catabolism

The breakdown of branched-chain amino acids into smaller molecules, analogous to fatty acid catabolism.

β-methylcrotonyl-CoA

An intermediate molecule formed during leucine catabolism.

Tiglyl-CoA

An intermediate molecule formed during isoleucine catabolism.

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Methacrylyl-CoA

An intermediate molecule formed during valine catabolism.

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Maple Syrup Urine Disease

A genetic disorder impacting the alpha-ketoacid decarboxylase complex, causing a build-up of branched-chain amino acids.

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Alpha-Ketoacid Decarboxylase Complex

A complex of enzymes crucial for breaking down branched-chain amino acids.

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Amino Acid Catabolism

The breakdown of amino acids (building blocks of proteins) to be used for energy or to synthesize other molecules.

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Branched-chain amino acid catabolism

The breakdown of leucine, isoleucine, and valine into smaller molecules. This process is similar to breaking down fatty acids.

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Hyperprolinemia types

Inherited metabolic disorders where the breakdown of proline is impaired, leading to elevated levels of proline in the blood.

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Hyperargininemia

Inherited metabolic disorder affecting arginine metabolism, leading to elevated arginine levels.

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Alpha-ketoacid dehydrogenase complex

A multi-enzyme complex that breaks down the molecule created from branched-chain amino acids after transamination step.

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Metabolic Fates of Catabolism

The different ways the products of amino acid breakdown are used by the body (e.g., energy production, synthesis of other molecules).

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Aminotransferase Reaction

A reaction that transfers an amino group from an amino acid to a keto acid, forming a new amino acid and a new keto acid.

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Glycine cleavage system

A multi-enzyme complex in mitochondria that breaks down glycine into CO2, NH4+, and N5,N10-methylenetetrahydrofolate.

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Kynurenine

A product of tryptophan breakdown.

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Phenylalanine Catabolism

The breakdown of phenylalanine, a pathway that's largely similar across the breakdown of several branched-chain amino acids.

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Folate deficiency

A condition where the body lacks folate (a B vitamin), which impairs the transfer of the formimino group in amino acid metabolism.

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Coenzyme in Transamination

A molecule, often vitamin B derived, that helps aminotransferases catalyze reactions.

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Vitamin B6 deficiency

Deficiency of vitamin B6

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Branched-Chain Amino Acids

Amino acids with branched carbon chains (e.g., leucine, isoleucine, valine).

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Hisitine metabolism disorders

Inherited problems in the processing of histidine, which can lead to histidinemia or urocanic aciduria.

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Hartnup disease

A condition affecting intestinal and renal transport of tryptophan and other neutral amino acids, leading to their excretion.

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Figlu excretion

Elevated excretion of formiminoglutamate(FIGLU) following a histidine load is a diagnostic indicator of folate deficiency.

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Aminoacidurias

Disorders related to abnormal amino acid metabolism and excretion in urine.

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Metabolic Defects

Genetic disorders affecting specific enzymes in the catabolic pathways of amino acids, leading to specific clinical issues.

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S-adenosylmethionine

An active form of methionine, produced via a reaction with ATP, which is instrumental in certain biochemical reactions.

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Propionyl-CoA

A molecule formed during the breakdown of methionine, which proceeds through reactions 2, 3, and 4 of Figure 19-2.

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Clinical Signs/Symptoms

Observable effects of the build-up of different metabolites caused by faulty enzymes in a metabolic pathway.

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Tandem Mass Spectrometry

A screening tool to detect metabolic defects in newborns by analyzing the breakdown products in a blood sample.

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Amino Acid Catabolism

The breakdown of amino acids into molecules that can be used for energy or to build other molecules.

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Metabolic Defects

Genetic disorders that impair specific enzymes involved in amino acid breakdown, causing buildup of harmful metabolites.

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Clinical Signs/Symptoms

Observable effects, such as brain damage, caused by the buildup of harmful metabolites due to faulty enzymes.

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Prenatal Diagnosis

Diagnosis of a condition or disorder before birth.

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Enzyme Mutations

Changes in DNA affecting enzyme production or function, often leading to metabolic diseases.

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Metabolic Fates

Ways the products of amino acid breakdown are utilized, such as energy production or synthesis of other molecules.

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Metabolite Buildup

Accumulation of substances that result from a disrupted metabolic pathway.

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Enzyme Activity

The ability of an enzyme to catalyze a biochemical reaction.

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Enzyme Structure

The three-dimensional arrangement of an enzyme's components, influencing its function.

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Metabolic Diseases

Disorders arising from defects in metabolic pathways, often concerning amino acid breakdown, resulting in specific clinical issues.

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Low Enzyme Efficiency

Reduced catalytic activity of a mutated enzyme, which impairs the speed at which it completes chemical tasks.

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Amino Acid Catabolism

The breakdown of amino acids for energy or synthesis of other molecules

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Metabolic Defects

Genetic disorders impairing amino acid breakdown, resulting in harmful metabolites.

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Clinical Signs/Symptoms

Observable effects of a buildup of harmful metabolites.

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Enzyme Mutations

Changes in DNA affecting enzyme production or function.

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Prenatal Diagnosis

Diagnosis of a condition or disorder before birth.

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Metabolic Fates

How products of amino acid breakdown are used.

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Metabolite Buildup

Accumulation of substances due to disrupted metabolic pathways

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Enzyme Activity

Enzyme's ability to catalyze biochemical reactions.

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Enzyme Structure

An enzyme's 3D arrangement of components; crucial for function.

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Metabolic Diseases

Disorders stemming from defects in metabolic pathways, esp. amino acid breakdown.

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Low Enzyme Efficiency

Reduced catalytic activity of mutated enzyme, slowing process.

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Transamination

The initial catabolic reaction for most amino acids; involves transferring an amino group to an alpha-keto acid to produce another amino acid and a new keto acid.

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Amino Acid Catabolism

The breakdown of amino acids, often for energy or to synthesize other molecules.

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Transaminase

An enzyme catalyzing transamination reactions.

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Alpha-Ketoglutarate

A common acceptor of amino groups in transamination reactions.

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Proline Catabolism

The breakdown pathway for proline, occurring in the mitochondria.

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Hyperprolinemia

Inherited disorders affecting proline breakdown, leading to elevated proline levels.

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amphibolic intermediate

A molecule that can be used in both catabolic and anabolic pathways.

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Nonketotic hyperglycinemia

A rare genetic disorder where glycine accumulates in body tissues, including the nervous system, due to an impaired glycine degradation pathway.

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Primary hyperoxaluria

A genetic defect preventing the breakdown of glyoxylate, leading to oxalates buildup, causing kidney stones (urolithiasis), kidney damage (nephrocalcinosis), and early death.

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Glycinuria

A condition where glycine is not reabsorbed by the kidneys, leading to its excretion in urine.

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Glycine degradation

The process of breaking down glycine into simpler molecules.

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Glycine Hydroxymethyltransferase

An enzyme that converts serine into glycine.

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Amino Acid Catabolism

The breakdown of amino acids for energy or to build other molecules.

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Metabolic Fates

How the products of amino acid breakdown are used (energy, molecule building).

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Metabolic Defects

Genetic problems in amino acid breakdown enzymes.

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Clinical Signs/Symptoms

Observable effects of buildup of harmful breakdown products.

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Remediation of Metabolic Disorders

Treatment, often dietary, for impaired amino acid metabolism.

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Gene Therapy

Techniques to permanently fix a metabolic defect.

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Amino Acid Interconvertibility

Conversion of amino acids to carbs, fats, or both.

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Carbohydrate and Lipid Biosynthesis

Amino acid breakdown intermediates create carbohydrates and lipids.

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Ketogenic Amino Acids

Amino acids that can be converted to fats.

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Glycogenic Amino Acids

Amino acids that can be converted to carbohydrates.

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Asparagine & Aspartate

Amino acids that can form oxaloacetate.

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Early Diagnosis of MSUD

Essential for preventing brain damage and early mortality in Maple Syrup Urine Disease (MSUD) by correcting dietary protein with an amino acid mixture.

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MSUD Genetic Heterogeneity

Mutations in genes encoding E1α, E1β, E2, and E3 enzymes lead to different MSUD subtypes.

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Type IA MSUD

MSUD subtype caused by mutations in the E1α gene.

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Type IB MSUD

MSUD subtype caused by mutations in the E1β gene.

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Type II MSUD

MSUD subtype caused by mutations in the E2 gene.

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Type III MSUD

MSUD subtype caused by mutations in the E3 gene.

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Branched-chain ketonuria

MSUD subtype where the α-ketoacid decarboxylase retains some activity, resulting in later-onset symptoms.

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Isovaleric acidemia

Metabolic disorder with elevated isovalerate due to impaired isovaleryl-CoA dehydrogenase enzyme activity.

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Protein-rich foods

Foods containing high levels of proteins, that cause a buildup of metabolites when processing amino acids in affected individuals.

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Tyrosine Catabolism

The breakdown of tyrosine into simpler molecules, ultimately to acetyl-CoA

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Type I Tyrosinemia

A metabolic disorder caused by a defect in fumarylacetoacetate hydrolase, leading to tyrosine accumulation and potential liver failure.

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Phenylketonuria (PKU) Screening

A test to detect elevated phenylalanine levels in newborns; increasingly done with tandem mass spectrometry.

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Fumarylacetoacetate Hydrolase

An enzyme catalyzing the final step in the tyrosine catabolic pathway; its deficiency causes Type I tyrosinemia.

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Tandem Mass Spectrometry

A powerful analytical technique used to screen for multiple metabolic disorders in newborns, including PKU.

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Metabolic Defects

Genetic disorders impairing specific enzymes in amino acid catabolic pathways.

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Clinical Signs/Symptoms

Observable effects of the buildup of harmful metabolites due to enzyme deficiencies in metabolic pathways.

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Phenylalanine Management

Restricting dietary phenylalanine intake to prevent mental retardation, without causing malnutrition, in patients with PKU.

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Phenylketonuria (PKU)

A genetic disorder causing a deficiency in the enzyme phenylalanine hydroxylase, leading to phenylalanine buildup in the body.

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Tryptophan Breakdown

Tryptophan is broken down via the kynurenine-anthranilate pathway, involving tryptophan oxygenase, an iron-porphyrin protein.

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Phenylalanine Hydroxylase

The enzyme responsible for converting phenylalanine to tyrosine. Defects in this enzyme cause PKU.

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Dietary Restriction (PKU)

A diet low in phenylalanine is crucial for preventing mental retardation in individuals with PKU.

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Prenatal Diagnosis

Diagnostic testing for metabolic defects like PKU before birth using DNA.

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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

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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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