Catabolism of Amino Acids and BCAAs
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Questions and Answers

What substance is formed when homogentisic acid oxidizes and polymerizes?

  • Melanin
  • Tyrosinase
  • Urocanic acid
  • Alkapton (correct)

    • What is a characteristic symptom of alkaptonuria?

  • Brown spots on skin
  • Deficiency of melanin
  • Urine resembling coke in color (correct)
  • Excessive sun sensitivity

    • What diagnostic test results in a green color when testing for homogentisic acid?

  • Urine culture test
  • Benedict's test
  • Ferric chloride test (correct)
  • Histidine load test

    • Which enzyme deficiency leads to albinism?

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

    What does excessive excretion of FIGlu in urine indicate?

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

    What is the first irreversible step in histidine catabolism?

    <p>Formation of urocanic acid</p> Signup and view all the answers

    What are the three common steps in the catabolism of branched chain amino acids?

    <p>Transamination, Oxidative decarboxylation, Dehydrogenation</p> Signup and view all the answers

    Where is the primary site for the catabolism of branched chain amino acids?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which amino acids are primarily involved in branched chain amino acid catabolism?

    <p>Leucine, Isoleucine, Valine</p> Signup and view all the answers

    What role do coenzymes play in the catabolism of branched chain amino acids?

    <p>They facilitate enzymatic reactions.</p> Signup and view all the answers

    How is the α-keto acid dehydrogenase complex regulated?

    <p>With covalent modification, phosphorylation, and dephosphorylation</p> Signup and view all the answers

    What is Maple Syrup Urine Disease associated with?

    <p>Deficiency of α-keto acid dehydrogenase complex</p> Signup and view all the answers

    What physical characteristics are associated with individuals suffering from Maple Syrup Urine Disease?

    <p>Urine with the odor of burnt sugar</p> Signup and view all the answers

    What impact does the accumulation of branched chain amino acids have on the body?

    <p>Impairs transport and function of other amino acids</p> Signup and view all the answers

    What can happen to the mental development of infants with Maple Syrup Urine Disease?

    <p>They may experience abnormal brain development leading to mental retardation</p> Signup and view all the answers

    What is the primary characteristic of phenylketonuria?

    <p>Accumulation of phenylalanine and phenylketones in the blood</p> Signup and view all the answers

    What specific odor is associated with the urine of individuals affected by phenylketonuria?

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

    Which of the following is a notable symptom of phenylketonuria?

    <p>Severe mental retardation</p> Signup and view all the answers

    What dietary change is crucial for managing phenylketonuria?

    <p>Restriction of phenylalanine-containing diets</p> Signup and view all the answers

    What is now considered an essential amino acid for individuals with phenylketonuria in early years?

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

    Which test is used to diagnose phenylketonuria by detecting phenylalanine levels in blood?

    <p>Guthrie test</p> Signup and view all the answers

    What byproduct is tested for in the urine during the diagnosis of phenylketonuria?

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

    What is one of the metabolic fates of tyrosine?

    <p>Creation of melanin pigment</p> Signup and view all the answers

    Where does the catabolism of tyrosine primarily occur?

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

    What condition is characterized by the accumulation and excretion of tyrosine and its metabolites?

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

    What is the primary characteristic of intermittent branched chain ketonuria?

    <p>Symptoms occur later in life and intermittently.</p> Signup and view all the answers

    What is the primary method for diagnosing isovalERIC acidaemia?

    <p>Urinary isovalerate levels and urine odor analysis.</p> Signup and view all the answers

    Which amino acid is primarily affected in isovalERIC acidaemia?

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

    What is the cofactor required for the hydroxylation of phenylalanine to tyrosine?

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

    What symptoms are associated with isovalERIC acidaemia when subjects are fed protein?

    <p>Vomiting, acidosis, and coma.</p> Signup and view all the answers

    What condition can result from deficiency in phenylalanine hydroxylase or related cofactors?

    <p>Phenylketonuria (PKU).</p> Signup and view all the answers

    In the catabolism of phenylalanine, what compound is formed after its hydroxylation?

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

    What condition is associated with the deficiency of fumarylacetoacetase?

    <p>Type I Tyrosinaemia</p> Signup and view all the answers

    How is intermittent branched chain ketonuria best managed?

    <p>Restriction of branched chain amino acids.</p> Signup and view all the answers

    Which of the following symptoms is NOT associated with the acute form of Type I Tyrosinaemia?

    <p>Cirrhosis of the liver</p> Signup and view all the answers

    What odor is typically associated with isovalERIC acidaemia?

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

    What metabolic issue is primarily noted in Type II Tyrosinaemia?

    <p>Accumulation of tyrosine and its metabolites</p> Signup and view all the answers

    What deficiency leads to accumulation and excretion of isovalerate in urine?

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

    What is a common symptom found in both acute Type I Tyrosinaemia and Type II Tyrosinaemia?

    <p>Poor appetite</p> Signup and view all the answers

    Which of the following is a characteristic feature of Type III Tyrosinaemia?

    <p>Periodic loss of balance</p> Signup and view all the answers

    In which condition do affected subjects excrete large amounts of homogentisic acid in their urine?

    <p>Homogentisic Aciduria</p> Signup and view all the answers

    Which type of Tyrosinaemia is also referred to as hepato-renal tyrosinaemia?

    <p>Type I</p> Signup and view all the answers

    What is the main cause of the symptoms associated with Type I Tyrosinaemia?

    <p>Accumulation of fumaryl acetoacetate</p> Signup and view all the answers

    What percentage of neonates may experience temporarily elevated levels of tyrosine?

    <p>10%</p> Signup and view all the answers

    Study Notes

    Fate of the Carbon Skeleton of Amino Acids

    • Amino acid carbon skeletons are broken down to produce energy or used to synthesize other molecules.
    • Different amino acids have different fates.
    • For branched-chain amino acids (BCAAs), their catabolism primarily occurs in skeletal muscle.

    Catabolism of Branched-Chain Amino Acids

    • The process begins with transamination, converting BCAAs into α-keto acids.
    • Oxidative decarboxylation, a critical step, occurs, involving a complex, and is then reduced into Acyl CoA thioester.
    • Finally, a series of dehydrogenation reactions convert the Acyl CoA.

    Leucine, Isoleucine & Valine

    • The primary site for catabolism of these branched-chain amino acids is skeletal muscle.
    • A specific aminotransferase begins the process within the cytosol.
    • This enzyme converts the amino acids to α-keto acids using α-ketoglutarate as an acceptor.
    • This reaction is called a transamination reaction.
    • Subsequent steps, involving a dehydrogenase complex, occur within the mitochondria.

    Catabolism of Leucine, Isoleucine & Valine

    • The α-keto acids undergo oxidative decarboxylation using a branched-chain α-keto acid dehydrogenase complex.
    • This multi-enzyme complex uses five coenzymes: Thiamine pyrophosphate (TPP), CoASH, Lipoamide, FAD, and NAD+.
    • The process converts the α-keto acids to the corresponding acyl CoA thioesters.

    Regulation of Catabolism

    • The branched-chain α-keto acid dehydrogenase complex activity is regulated through covalent modification.
    • Phosphorylation inactivates the complex.
    • Dephosphorylation activates the complex.
    • This regulation responds to dietary branched-chain amino acids.

    Maple Syrup Urine Disease (MSUD)

    • A deficiency in the branched-chain α-keto acid dehydrogenase complex causes MSUD.
    • It's marked by the build-up of branched-chain α-keto acids in the blood, excreted in the urine.
    • Urine and sweat have a distinctive maple syrup or burnt sugar odor.
    • MSUD can lead to mental retardation and death if left untreated.
    • Dietary restriction of branched-chain amino acids is a crucial management strategy.
    • Some patients respond to thiamine supplementations.

    Intermittent Branched-Chain Ketonuria (IBCK)

    • A less severe form of MSUD, characterized by less severe deficiency in the branched-chain α-keto acid dehydrogenase complex.
    • Symptoms typically appear later in life and are intermittent.
    • Dietary restriction of branched-chain amino acids is more effective than in other MSUD forms.

    Isovaleric Acidemia

    • Deficiency in isovaleryl CoA dehydrogenase, an enzyme required for leucine catabolism.
    • Leads to the accumulation and excretion of isovalerate (isovaleric acid).
    • Urine and breath of affected individuals exhibit a "cheesy" odor.
    • Affected individuals may experience vomiting, acidosis, and coma (especially during protein intake).
    • Managed by restricting dietary leucine intake.

    Catabolism of Phenylalanine

    • Phenylalanine is usually hydroxylated to tyrosine by phenylalanine hydroxylase in the liver.
    • The reaction requires tetrahydrobiopterin (BH4) as a cofactor.

    Phenylketonuria (PKU)

    • Results from a deficiency in phenylalanine hydroxylase or the enzyme that regenerates BH4.
    • Leads to the accumulation of phenylalanine and phenylketones in the blood.
    • This results in excretion in the urine.
    • The condition, if left untreated, potentially leads to mental retardation.
    • Patients should strictly limit dietary phenylalanine intake, alongside introducing tyrosine to the diet.

    Catabolism of Tyrosine

    • Tyrosine breakdown through a series of reactions leads to the production of fumarate and acetoacetate.
    • The process includes transamination, dioxygenation, isomerization, and hydrolysis reactions.
    • Liver is the main site of tyrosine catabolism.

    Tyrosinaemia

    • Characterized by the buildup and excretion of tyrosine and its metabolic products in the body.
    • This can arise from different deficiencies which vary in severity.
    • In some cases, it is temporary due to vitamin C deficiency or immature liver enzyme function; in other cases, it is more severe and becomes chronic.

    Type I Tyrosinaemia

    • Caused by a deficiency in fumarylacetoacetate hydrolase.
    • Fumaryl-acetoacetate and fumaryl-acetoacetate accumulate, causing liver and kidney damage.
    • Can present in acute and chronic forms, with unique symptoms.

    Type II Tyrosinaemia

    • Deficiency in tyrosine aminotransferase leads to accumulation and excretion of tyrosine.
    • Associated with eye and skin abnormalities and, less frequently, with mental retardation.

    Type III Tyrosinaemia

    • Characterized by a deficiency in para-hydroxyphenylpyruvate dioxygenase.
    • The condition displays diverse characteristics in terms of symptoms.

    Homogentisic Aciduria (Alkaptonuria)

    • A deficiency in homogentisate 1,2-dioxygenase leads to homogentisic acid accumulation and excretion in the urine.
    • The urine darkens on exposure to air due to the formation of alkapton.
    • Can lead to ochronosis (discoloration of connective tissue) and arthritis in later life.

    Melanin Synthesis

    • Melanin, the pigment in skin, hair, and eyes, is synthesized within melanosomes within melanocytes.
    • The process starts with L-tyrosine, followed by the action of tyrosinase.

    Albinism

    • A genetic disorder where the enzyme tyrosinase is deficient, leading to reduced or absent melanin production in skin, hair, and eyes.
    • Affected individuals are highly susceptible to sunlight and skin cancer.

    Catabolism of Histidine

    • Histidine catabolism begins with the irreversible conversion of histidine to urocanic acid, catalyzed by histidine ammonia lyase.
    • Urocanic acid is later converted to formiminoglutamate (FIGLU).
    • FIGLU is converted further, requiring folate or vitamin B12.

    Histidinaemia

    • A condition resulting from a deficiency in histidine ammonia lyase (HAA).
    • Characterized by elevated blood and urine levels of histidine.
    • Some cases are accompanied by speech impairment and/or mental retardation.

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    Amino Acid Catabolism PDF

    Description

    This quiz explores the fate of amino acid carbon skeletons, focusing on the catabolism of branched-chain amino acids (BCAAs) like leucine, isoleucine, and valine. It delves into the biochemical processes involved, such as transamination and oxidative decarboxylation, that take place primarily in skeletal muscle. Challenges await you to test your understanding of these metabolic pathways.

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