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

What does excessive excretion of FIGlu in urine indicate?

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

What is the first irreversible step in histidine catabolism?

<p>Formation of urocanic acid (D)</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 (A)</p> Signup and view all the answers

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

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

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

<p>Leucine, Isoleucine, Valine (A)</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. (B)</p> Signup and view all the answers

How is the α-keto acid dehydrogenase complex regulated?

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

What is Maple Syrup Urine Disease associated with?

<p>Deficiency of α-keto acid dehydrogenase complex (D)</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 (B)</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 (A)</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 (B)</p> Signup and view all the answers

What is the primary characteristic of phenylketonuria?

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

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

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

Which of the following is a notable symptom of phenylketonuria?

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

What dietary change is crucial for managing phenylketonuria?

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

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

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

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

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

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

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

What is one of the metabolic fates of tyrosine?

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

Where does the catabolism of tyrosine primarily occur?

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

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

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

What is the primary method for diagnosing isovalERIC acidaemia?

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

Which amino acid is primarily affected in isovalERIC acidaemia?

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

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

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

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

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

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

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

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

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

What condition is associated with the deficiency of fumarylacetoacetase?

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

How is intermittent branched chain ketonuria best managed?

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

What odor is typically associated with isovalERIC acidaemia?

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

What metabolic issue is primarily noted in Type II Tyrosinaemia?

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

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

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

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

<p>Periodic loss of balance (C)</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 (B)</p> Signup and view all the answers

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

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

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

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

Flashcards

Catabolism of Branched-Chain Amino Acids

The breakdown of leucine, isoleucine, and valine into energy or other molecules.

Transamination

The transfer of an amino group from one molecule to another, forming an α-keto acid.

Oxidative Decarboxylation (BCKD)

Conversion of α-keto acids to acyl-CoA molecules in mitochondria.

Acyl-CoA Dehydrogenase

An enzyme that further processes acyl CoA molecules.

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Branched-Chain α-Keto Acid Dehydrogenase Complex (BCKDC)

The key enzyme complex for oxidative decarboxylation of BCAAs.

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Maple Syrup Urine Disease (MSUD)

A genetic disorder caused by a deficiency in BCKDC, leading to the accumulation of BCAAs and their byproducts in the urine.

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α-keto acids

Molecules formed after transamination, important intermediates in BCAA catabolism.

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Covalent Modification

Regulation of BCKDC activity through phosphorylation and dephosphorylation by kinases and phosphatases, respectively.

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Primary site of BCAA catabolism

Skeletal muscle is the main location for the catabolism of branched-chain amino acids.

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Intermittent Branched-Chain Ketonuria

A less severe form of MSUD characterized by an intermittent deficiency of the α-keto acid dehydrogenase complex, with symptoms appearing later in life.

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Branched-chain amino acids

Essential amino acids whose intake is restricted to manage certain metabolic disorders like intermittent branched-chain ketonuria.

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Isovaleric acidemia

A metabolic disorder caused by a deficiency of isovaleryl CoA dehydrogenase, leading to the accumulation and excretion of isovalerate.

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Isovalerate

A specific substance that accumulates and is excreted in the urine (and breath) with Isovaleric acidemia, giving a 'cheesy' odor.

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Leucine

An amino acid whose restricted intake can help manage isovaleric acidemia, as it is responsible for the production of isovalerate.

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Phenylalanine Hydroxylase

An enzyme crucial for converting phenylalanine to tyrosine.

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Phenylketonuria (PKU)

A metabolic disorder caused by a deficiency in phenylalanine hydroxylase, resulting in high phenylalanine levels.

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Tetrahydrobiopterin

A cofactor required for the phenylalanine hydroxylase reaction converting phenylalanine into tyrosine.

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Catabolism of Phenylalanine

The breakdown process involving converting phenylalanine into tyrosine with the help of phenylalanine hydroxylase and cofactor tetrahydrobiopterin.

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Dihydrobiopterin Reductase

Enzyme that regenerates tetrahydrobiopterin, essential for the phenylalanine hydroxylase reaction.

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Phenylketonuria (PKU)

A genetic disorder causing phenylalanine buildup in the blood and urine due to a faulty enzyme.

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PKU Symptoms

Mental retardation, low IQ, poor growth, and hypopigmentation (lightened hair and skin).

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PKU Urine Odor

The urine of PKU patients has a "mousy" odor due to phenylacetate.

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PKU Diet Management

Restricts phenylalanine intake and promotes tyrosine in the diet for the first years.

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PKU Diagnosis - Guthrie Test

A blood test that checks for phenylalanine levels using bacterial inhibition.

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PKU Diagnosis - Ferric Chloride Test

Urine test used to detect phenylpyruvate.

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Tyrosine Metabolism

Tyrosine can become neurotransmitters, hormones, and pigment.

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Tyrosine Catabolism

Breakdown of tyrosine into acetoacetate and fumarate in the liver.

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Tyrosinemia

Condition characterized by an accumulation of tyrosine and its metabolites.

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Tetrahydrobiopterin

A substance important for PKU treatment and involved in tyrosine metabolism.

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Homogentisic Aciduria

A genetic disorder where homogentisic acid builds up in the body, turning urine dark and causing arthritis later in life.

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Albinism

A genetic condition causing a lack of melanin (pigment) in skin, hair, and eyes due to defective tyrosinase enzyme.

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Histidine Catabolism

The breakdown of histidine into other molecules, potentially influenced by folate or B12 deficiencies.

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FIGLU (Formiminoglutamate)

A byproduct of histidine metabolism; its accumulation in urine can indicate folate deficiency.

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Folate Deficiency

A condition where the body doesn't have enough folate, leading to FIGLU buildup in urine & impacting DNA synthesis.

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Melanin Synthesis

Process of forming melanin in melanosomes within melanocytes, crucial for skin, hair, and eye color.

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Tyrosinaemia

A genetic disorder causing tyrosine buildup in tissues, leading to potential medical problems.

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Type I Tyrosinaemia

A tyrosinaemia form due to fumarylacetoacetase deficiency, causing oxidative damage & cell death.

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Acute Type I Tyrosinaemia

Early-onset form, appearing in first few months of life, marked by poor appetite, etc.

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Chronic Type I Tyrosinaemia

Later-onset form, developing around one year, causing liver cirrhosis & kidney issues.

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Type II Tyrosinaemia

Caused by tyrosine aminotransferase deficiency, causing eye and skin problems.

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Type III Tyrosinaemia

Deficiency of para-hydroxy phenylpyruvate dioxygenase causing intellectual disability & seizures.

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Homogentisate-1,2-dioxygenase Deficiency

The cause of Alkaptonuria, resulting in excess homogentisic acid in urine.

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Tyrosine Elevation in Neonates

Temporary rise in tyrosine levels in newborns, potentially from vitamin C deficiency or immature livers.

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Vit C Deficiency

Can lead to elevated tyrosine levels in newborns.

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Fumaryl Acetoacetate

Accumulates in Type I tyrosinaemia, causing oxidative damage.

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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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