Lippincott's Biochemistry Chapter 20 - Amino Acids (Degradation and Synthesis)
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Questions and Answers

Which of the following amino acids is a precursor of cysteine?

  • Tyrosine (correct)
  • Phenylalanine
  • Arginine
  • Histidine

    • Which metabolic defect is characterized by an inability to fully metabolize phenylalanine?

  • Alkaptonuria
  • Albinism
  • Homocystinuria
  • Phenylketonuria (correct)

    • Which of the following amino acids is primarily classified as glucogenic?

  • Isoleucine
  • Histidine (correct)
  • Lysine
  • Leucine

    • What is a primary characteristic of ketogenic amino acids?

    <p>They can lead to the formation of ketone bodies.</p> Signup and view all the answers

    Which of the following is NOT associated with defects in amino acid metabolism?

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

    The removal of the alpha-amino group in amino acid metabolism is primarily involved in which process?

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

    Which metabolic condition is most directly linked to a deficiency in the enzyme responsible for converting methionine to homocysteine?

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

    Phenylalanine is primarily involved in the synthesis of which precursor amino acid?

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

    In patients with phenylketonuria, why is the dietary restriction of phenylalanine crucial?

    <p>To avoid the buildup of toxic levels of phenylalanine.</p> Signup and view all the answers

    What is the significance of tyrosine in the diet of individuals with phenylketonuria?

    <p>Tyrosine must be supplied in the diet as it becomes essential.</p> Signup and view all the answers

    Which of the following statements concerning amino acid catabolism is correct?

    <p>Amino acids catabolized to acetyl CoA are considered ketogenic.</p> Signup and view all the answers

    What dietary intervention is recommended for children diagnosed with classic phenylketonuria?

    <p>Implement lifelong restriction on phenylalanine intake.</p> Signup and view all the answers

    Which statement accurately describes a metabolic defect related to phenylketonuria?

    <p>Accumulation of phenylalanine leads to developmental issues.</p> Signup and view all the answers

    Which amino acid category is primarily associated with the production of ketone bodies?

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

    What is the primary result of defects in the enzymes responsible for amino acid metabolism?

    <p>Metabolic disorders related to amino acid degradation</p> Signup and view all the answers

    Which of the following substances is directly involved in the metabolism of oxaloacetate?

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

    Which metabolic pathway do glucogenic amino acids primarily support?

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

    What is one characteristic of metabolic defects related to amino metabolism?

    <p>They are often due to enzyme deficiencies</p> Signup and view all the answers

    Which amino acid is typically categorized as both ketogenic and glucogenic?

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

    Which of the following accurately describes the role of succinyl CoA in metabolic pathways?

    <p>It is involved in the metabolism of both ketogenic and glucogenic pathways</p> Signup and view all the answers

    What defines a ketogenic amino acid in contrast to a glucogenic amino acid?

    <p>It is converted into acetyl CoA or acetoacetate</p> Signup and view all the answers

    Metabolic defects in which of the following amino acid pathways are known to cause urea cycle disorders?

    <p>Glucogenic pathway</p> Signup and view all the answers

    Which amino acid is most commonly considered to have solely a glucogenic function?

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

    What is the primary consequence of amino acid degradation?

    <p>Formation of intermediate products for intermediary metabolism.</p> Signup and view all the answers

    Which of the following amino acids are classified as essential?

    <p>Lysine and isoleucine.</p> Signup and view all the answers

    Which intermediate product is NOT formed from amino acid degradation?

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

    What is the primary function of glucogenic amino acids?

    <p>They can be converted into glucose.</p> Signup and view all the answers

    Which of the following is true regarding metabolic defects in amino acid metabolism?

    <p>They can result in serious disease.</p> Signup and view all the answers

    Which of the following amino acids is primarily ketogenic?

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

    What process occurs after the removal of the a-amino group in amino acid degradation?

    <p>Catabolism of cx-keto acids.</p> Signup and view all the answers

    Which product during amino acid degradation contributes to energy production through the TCA cycle?

    <p>Succinyl CoA</p> Signup and view all the answers

    Which of the following statements correctly reflects the nature of essential amino acids?

    <p>They must be obtained exclusively from dietary sources.</p> Signup and view all the answers

    Which metabolic pathway do ketogenic amino acids primarily enter?

    <p>TCA cycle</p> Signup and view all the answers

    What is likely a consequence of a deficiency in dihydropteridine reductase?

    <p>Decreased levels of serotonin</p> Signup and view all the answers

    Which vitamin is NOT associated with the enzymatic reactions involving aromatic amino acid hydroxylases?

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

    What compound is used in the screening of newborns for metabolic disorders?

    <p>Heel prick blood samples</p> Signup and view all the answers

    Which of the following is true regarding the metabolic defect in phenylketonuria (PKU)?

    <p>PKU causes elevated levels of phenylalanine in the blood</p> Signup and view all the answers

    What type of amino acids can lead to the production of ketone bodies upon degradation?

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

    Which amino acid is a direct precursor to serotonin?

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

    What is the primary compound produced from the hydroxylation of phenylalanine?

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

    Which of the following statements about amino acid metabolism is incorrect?

    <p>Phenylketones are not present in the urine of PKU patients.</p> Signup and view all the answers

    Which statement is true about the effects of dihydropteridine reductase deficiency?

    <p>It leads to an inability to convert phenylalanine to tyrosine.</p> Signup and view all the answers

    What is a potential clinical outcome when treating hyperphenylalaninemia?

    <p>Unpredictable responses to enzyme replacement</p> Signup and view all the answers

    Which of the following conditions is characterized by a defect in the metabolism of tyrosine?

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

    Homocystinuria is primarily linked to a deficiency in the metabolism of which amino acid?

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

    Which condition is characterized by an accumulation of homogentisic acid due to a defect in the metabolism of phenylalanine?

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

    Which amino acid serves as a precursor to histamine?

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

    What is the primary metabolic defect associated with methylmalonic acidemia?

    <p>Vitamin B12 deficiency</p> Signup and view all the answers

    What is the significance of intermediates produced during amino acid catabolism?

    <p>They are utilized in the synthesis of glucose and fatty acids.</p> Signup and view all the answers

    Which of the following accurately describes the relationship between amino acid catabolism and the TCA cycle?

    <p>Both glucogenic and ketogenic amino acids can yield products that enter the TCA cycle.</p> Signup and view all the answers

    Which biochemical process follows the removal of the alpha-amino group in amino acid degradation?

    <p>Oxidative deamination to generate ammonia.</p> Signup and view all the answers

    Which of the following statements about ketogenic amino acids is correct?

    <p>They are directly converted into ketone bodies during metabolism.</p> Signup and view all the answers

    What is a likely consequence of defects in metabolic pathways of amino acid catabolism?

    <p>Accumulation of toxic intermediates.</p> Signup and view all the answers

    Which compound is most critical in the catabolism of both glucogenic and ketogenic amino acids?

    <p>Oxaloacetate.</p> Signup and view all the answers

    Which metabolic pathway can be directly affected by dietary restrictions caused by metabolic disorders?

    <p>Urea cycle.</p> Signup and view all the answers

    What is the primary reason for screening newborns for the possibility of phenylketonuria?

    <p>To avoid false negatives by screening after protein feeding</p> Signup and view all the answers

    Why is prenatal diagnosis of classic PKU complicated?

    <p>There are over 100 different mutations in the PAH gene</p> Signup and view all the answers

    What dietary intervention is crucial for managing phenylketonuria?

    <p>Synthetic amino acid preparations free of phenylalanine</p> Signup and view all the answers

    How is blood phenylalanine level managed in patients with phenylketonuria?

    <p>By maintaining it close to the normal range with dietary adjustments</p> Signup and view all the answers

    What developmental issues can arise from high blood phenylalanine levels in a mother during pregnancy?

    <p>Microcephaly and congenital heart abnormalities</p> Signup and view all the answers

    What is a metabolic characteristic of classic phenylketonuria in newborns?

    <p>Presence of both heterozygous mutations in the PAH gene</p> Signup and view all the answers

    Which of the following symptoms is characteristic of Maple Syrup Urine Disease (MSUD)?

    <p>Sweet-smelling urine</p> Signup and view all the answers

    What consequence arises from excessive dietary phenylalanine in untreated individuals with PKU?

    <p>Potential intellectual disability and neurological damage</p> Signup and view all the answers

    Which factor is key to the timing of newborn screening for PKU?

    <p>Timing relative to first feeding and protein exposure</p> Signup and view all the answers

    In the context of MSUD, what is the consequence of delayed treatment?

    <p>Intellectual disability</p> Signup and view all the answers

    What is the inheritance pattern of Maple Syrup Urine Disease?

    <p>Autosomal recessive</p> Signup and view all the answers

    What is one of the primary challenges in providing treatment for individuals with PKU?

    <p>Maintaining adherence to lifelong dietary restrictions</p> Signup and view all the answers

    Which of the following statements correctly reflects the nature of phenylketonuria metabolism?

    <p>It involves a genetic defect inhibiting phenylalanine metabolism</p> Signup and view all the answers

    Which enzyme complex is deficient in individuals with classic MSUD?

    <p>BCKD (branched-chain keto acid dehydrogenase)</p> Signup and view all the answers

    Among the following, what is a common clinical presentation in an infant with MSUD?

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

    What dietary intervention is crucial for mothers with high blood phenylalanine levels prior to conception?

    <p>Reduction of dietary phenylalanine</p> Signup and view all the answers

    What is the major toxic effect of elevated levels of BCKD substrates in MSUD?

    <p>Neurological dysfunction</p> Signup and view all the answers

    What is a primary feature of the classic neonatal-onset form of MSUD?

    <p>Immediate detection through newborn screening</p> Signup and view all the answers

    Which of the following amino acids accumulates significantly in the blood of MSUD patients?

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

    What is one of the key symptoms of alkaptonuria?

    <p>Accumulation of homogentisic acid</p> Signup and view all the answers

    Which type of dietary modification is effective in managing levels of homogentisic acid?

    <p>Limit dietary intake of phenylalanine and tyrosine</p> Signup and view all the answers

    What does the term 'ochronosis' refer to in the context of alkaptonuria?

    <p>Black pigment deposition in cartilage</p> Signup and view all the answers

    Why are infants typically asymptomatic in alkaptonuria?

    <p>Symptoms do not present until adulthood</p> Signup and view all the answers

    What distinguishes glucogenic amino acids from ketogenic amino acids?

    <p>Glucogenic amino acids are primarily catabolized to glucose precursors</p> Signup and view all the answers

    What is the primary characteristic of the urine in patients with alkaptonuria after standing?

    <p>It darkens due to oxidation of homogentisic acid</p> Signup and view all the answers

    What form of arthritis is commonly associated with alkaptonuria?

    <p>Early onset arthritis in large joints</p> Signup and view all the answers

    Which amino acids are involved in the metabolic pathway of tyrosine?

    <p>Phenylalanine and phenylacetate</p> Signup and view all the answers

    What is a common clinical finding in elderly patients with alkaptonuria?

    <p>Severe crippling arthritis</p> Signup and view all the answers

    Match the following amino acids with their associated metabolic processes:

    <p>Glutamine = Converted to glutamate and ammonia by glutaminase Proline = Oxidized to glutamate Arginine = Hydrolyzed to ornithine and urea by arginase Asparagine = Converted to aspartate by asparaginase</p> Signup and view all the answers

    Match the following amino acids to their products in metabolism:

    <p>Glutamine = Produces glutamate Proline = Produces glutamate Arginine = Produces ornithine Asparagine = Produces aspartate</p> Signup and view all the answers

    Match the following amino acids to their role in the urea cycle:

    <p>Glutamine = Source of nitrogen for urea synthesis Proline = Transamination to produce a-ketoglutarate Arginine = Converted to ornithine in the urea cycle Asparagine = Required for aspartate formation</p> Signup and view all the answers

    Match the amino acids with their pathways leading to a-ketoglutarate:

    <p>Glutamine = Transaminated to a-ketoglutarate Proline = Oxidatively deaminated to a-ketoglutarate Arginine = Converted to a-ketoglutarate via ornithine Asparagine = Deprived from the blood in leukemia therapy</p> Signup and view all the answers

    Match the following amino acids with their clinical significance:

    <p>Glutamine = Supplementation improves outcomes in trauma Proline = Participates in collagen synthesis Arginine = Involved in immune response and healing Asparagine = Essential for rapidly dividing leukemic cells</p> Signup and view all the answers

    Match the following components of phenylketonuria (PKU) with their descriptions:

    <p>Phenylalanine = An essential amino acid that is limited in PKU PAH gene = Gene encoding phenylalanine hydroxylase Prenatal diagnosis = Diagnosis method identifying mutations before birth Synthetic amino acid preparations = Dietary treatment to manage blood phenylalanine levels</p> Signup and view all the answers

    Match the following dietary components with their relevance in PKU management:

    <p>Fruits = Low in phenylalanine Vegetables = Natural food included in PKU diet Cereals = Selected for low phenylalanine content Natural protein = Contains excessive phenylalanine for PKU patients</p> Signup and view all the answers

    Match the following statements regarding PKU with their correct implications:

    <p>Positive screening test = Indicates further testing is required Normal diet = Leads to increased phenylalanine levels Quantitative determination = Confirms diagnosis via phenylalanine levels Heterozygous condition = Presence of different mutations in PAH gene</p> Signup and view all the answers

    Match the following types of PKU with their characteristics:

    <p>Classic PKU = Caused by mutations in the PAH gene Non-classic PKU = Milder form with different residual activity Prenatal PKU diagnosis = Identifies mutations in unborn children Dietary intervention = Involves limiting phenylalanine intake</p> Signup and view all the answers

    Match the following consequences of untreated PKU with their outcomes:

    <p>High phenylalanine levels = Can lead to intellectual disability Lifelong management = Requires strict dietary adherence Early diagnosis = Improves treatment outcomes Neurological damage = Result of uncontrolled phenylalanine exposure</p> Signup and view all the answers

    Study Notes

    Amino Acid Degradation and Synthesis

    • Amino acid degradation removes the α-amino group, catabolizes the resulting α-keto acids (carbon skeletons)
    • Pathways converge to form seven intermediate products (oxaloacetate, pyruvate, α-ketoglutarate, fumarate, succinyl CoA, acetyl CoA, acetoacetate)
    • These enter intermediate metabolism, producing glucose, ketone bodies, lipids, or energy through TCA cycle oxidation to CO2
    • Nonessential amino acids can be synthesized from metabolic intermediates or from essential amino acids
    • Essential amino acids must be obtained from the diet for protein synthesis
    • Genetic defects in amino acid pathways can cause disease

    Glucogenic and Ketogenic Amino Acids

    • Amino acids are classified as glucogenic, ketogenic, or both based on their catabolism to seven intermediate products
    • Glucogenic: Catabolism produces pyruvate or TCA cycle intermediates, able to produce glucose in the liver and kidney
    • Ketogenic: Catabolism yields acetoacetate or precursors (acetyl CoA, acetoacetyl CoA), cannot produce glucose
    • Leucine and lysine are exclusively ketogenic
    • Amino acid catabolism pathways are organized based on the seven intermediate products they produce

    Amino Acid Carbon Skeleton Catabolism

    • Pathways of amino acid catabolism organized by the intermediate they produce (oxaloacetate, etc.)
    • Asparagine: Hydrolyzed by asparaginase to ammonia and aspartate, then transaminated to oxaloacetate
    • Glutamine: Hydrolyzed to glutamate and ammonia by glutaminase, converted to α-ketoglutarate via transamination or oxidative deamination
    • Proline: Oxidized to glutamate, then transaminated or oxidatively deaminated to α-ketoglutarate
    • Arginine: Hydrolyzed to ornithine, then subsequently converted to α-ketoglutarate with glutamate semialdehyde as an intermediate
    • Histidine: Oxidatively deaminated to urocanic acid, then N-formiminoglutamate that donates its formimino group to THF

    Amino acids that form Pyruvate

    • Alanine loses its amino group via transamination to form pyruvate
    • Serine can be converted to glycine, or pyruvate
    • Glycine can be deaminated to glyoxylate, which is oxidized to oxalate or transaminated to glycine
    • Cysteine: Desulfurization yields pyruvate
    • Threonine is converted to pyruvate

    Amino Acids that form Fumarate

    • Phenylalanine produces tyrosine via hydroxylation
    • Phenylalanine and tyrosine catabolism merges, producing fumarate and acetoacetate
    • Inherited deficiencies in phenylalanine and tyrosine metabolism lead to diseases like PKU, tyrosinemia, and albinism

    Amino Acids that form Succinyl CoA (Methionine)

    • Methionine forms S-adenosylmethionine (SAM), a methyl group donor
    • Methionine catabolism results in homocysteine (Hcy)
    • Hcy can be remethylated to methionine or enter the transsulfuration pathway to form cysteine

    Other Amino Acids that form Succinyl CoA

    • Valine, isoleucine, and threonine catabolism produce succinyl CoA
    • Valine and isoleucine are branched-chain amino acids (BCAAs)
    • Their catabolism generates propionyl CoA, converted to methylmalonyl CoA and then succinyl CoA

    Amino Acid Metabolism Disorders

    • Single-gene disorders are a subset of inborn errors, caused by mutations

    • Mutations typically lead to abnormal proteins, often enzymes

    • Disorders result in intellectual disability or developmental issues due to metabolite accumulation

    • Phenylketonuria (PKU): Deficiency in phenylalanine hydroxylase (PAH)

    • Elevated phenylalanine levels cause intellectual disability, developmental delay, and other complications

    • Treatment involves dietary restrictions, restricting phenylalanine and supplementing with tyrosine

    • Maple syrup urine disease: Deficiency in branched-chain α-keto acid dehydrogenase (BCKD)

    • Accumulation of branched-chain amino acids and α-keto acids, leading to toxic effects

    • Treatment involves dietary restrictions for the amino acids to prevent neurologic complications

    • Albinism: Defect in tyrosine metabolism, resulting in reduced melanin

      • Reduced melanin leads to reduced pigmentation in skin, hair, and eyes
      • Increased risk of skin cancer

    • Homocystinuria: Defects in homocysteine metabolism

      • High homocysteine levels and low cysteine levels
      • Symptoms include lens dislocation, skeletal abnormalities, intellectual disability, and thrombosis risk
      • Treatment involves methionine restriction and supplementation with B12 and folate

    • Alkaptonuria: Deficiency in homogentisic acid oxidase

      • Accumulation of homogentisic acid causes dark urine and joint problems (arthritis)
      • Deposition of black pigment ('ochronosis') in cartilage and connective tissue

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    Lippincott's Biochemistry Chapter 20 - Amino Acids (Degradation and Synthesis) PDF

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    This quiz covers the degradation and synthesis of amino acids, including their metabolic pathways and classification as glucogenic or ketogenic. Understand the importance of essential and nonessential amino acids, as well as the impact of genetic defects on metabolism.

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