Amino Acid Metabolism Quiz
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Questions and Answers

What is the main cause of phenylketonuria (PKU)?

  • Defect in kidney transport of cysteine
  • Enzyme deficiency in branched chain amino acid catabolism
  • Inability to convert phenylalanine to tyrosine (correct)
  • Lack of homogentisate dioxygenase

    • In alkaptonuria, patients can effectively break down proteins to amino acids like tyrosine and phenylalanine.

    False

    What is the primary cause of nonketotic hyperglycinemia?

  • Accumulation of phenylalanine
  • Defective tyrosine hydroxylase enzyme
  • Defective creatine synthesis
  • Defects in the enzyme complex that catalyzes glycine cleavage (correct)

    • What is a common symptom of cystinuria?

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

    Individuals with nonketotic hyperglycinemia typically live to adulthood.

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

    The enzyme deficiency in alkaptonuria is __________.

    <p>homogentisate dioxygenase</p> Signup and view all the answers

    What are the starting materials in heme synthesis?

    <p>Glycine and succinyl CoA</p> Signup and view all the answers

    Creatine is synthesized from ______ and glycine.

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

    Match the following diseases with their characteristics:

    <p>Phenylketonuria = High phenylalanine levels Alkaptonuria = Black urine and arthritis Cystinuria = Defect in kidney transport Gyrate Atrophy = Tunnel vision and blindness</p> Signup and view all the answers

    Which compound is a catabolic product of creatine?

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

    What dietary restriction can help slow the progress of gyrate atrophy?

    <p>Decreased arginine intake</p> Signup and view all the answers

    Elevated levels of phenylpyruvate are beneficial for brain development in children with PKU.

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

    Match the following disorders with their related amino acid metabolism:

    <p>Nonketotic hyperglycinemia = Glycine cleavage defect Phenylketonuria = Phenylalanine hydroxylase deficiency Alkaptonuria = Homogentisate oxidase deficiency Cystinuria = Cystine transport defect</p> Signup and view all the answers

    Catecholamines are synthesized directly from glycine.

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

    Name one consequence of untreated phenylketonuria.

    <p>Brain damage</p> Signup and view all the answers

    Cystine accumulates in the blood and oxidizes to __________, causing calculi.

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

    What is the role of dopamine in the brain?

    <p>Acts as a neurotransmitter</p> Signup and view all the answers

    The process of measuring creatinine in urine helps to assess ______ function.

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

    What is typically tested in newborn screenings for PKU?

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

    Which of the following amino acids is the starting point for catecholamine synthesis?

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

    Which of the following disorders is caused by a deficiency in phenylalanine hydroxylase?

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

    Tyrosine is synthesized from phenylalanine in a process involving tetrahydrobiopterin.

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

    What are the end products of phenylalanine degradation?

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

    Phenylketonuria can lead to severe __________ if left untreated.

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

    Match the following disorders with their associated characteristics:

    <p>Glycine Encephalopathy = No known treatment, causes neurological issues Alkaptonuria = Black urine due to homogentisic acid Tyrosine Synthesis = Involves phenylalanine hydroxylase Cystinuria = Cystine stones in the kidneys</p> Signup and view all the answers

    Which amino acid is considered both glucogenic and ketogenic?

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

    Alkaptonuria is a result of an inability to metabolize phenylalanine.

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

    What is the consequence of lysine degradation in metabolism?

    <p>Produces acetyl CoA and contributes to fatty acids or ketone bodies.</p> Signup and view all the answers

    A common treatment for Phenylketonuria (PKU) is a __________-restricted diet.

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

    Which coenzyme is essential for the conversion of phenylalanine to tyrosine?

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

    Which condition results from a deficiency in the phenylalanine hydroxylase enzyme?

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

    Alkaptonuria is characterized by the accumulation of homogentisic acid.

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

    What neurotransmitter is produced from the decarboxylation of glutamate?

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

    A defect in the pathway of __________ synthesis can lead to albinism.

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

    Match the disorder with its metabolic defect:

    <p>Glycine Encephalopathy = Deficiency of glycine cleavage system Cystinuria = Impaired renal tubular reabsorption of cystine Phenylketonuria = Deficiency of phenylalanine hydroxylase Alkaptonuria = Deficiency of homogentisate oxidase</p> Signup and view all the answers

    Which of the following substances is derived from tryptophan?

    <p>Both A and B</p> Signup and view all the answers

    Tyrosine is produced by the hydroxylation of phenylalanine.

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

    Which hormone is produced by the thyroid gland that is derived from tyrosine?

    <p>Triiodothyronine (T3) or Tetraiodothyronine (T4)</p> Signup and view all the answers

    Norepinephrine and epinephrine are often referred to as __________ hormones.

    <p>fight-or-flight</p> Signup and view all the answers

    What is the main role of serotonin outside the central nervous system?

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

    Study Notes

    Phenylketonuria (PKU)

    • Individuals with PKU cannot convert phenylalanine to tyrosine.
    • This results in high levels of phenylalanine and low levels of tyrosine in the blood.
    • Phenylalanine is metabolized to phenylpyruvate instead.
    • Elevated levels of phenylpyruvate inhibit brain development.
    • Newborns are screened for PKU by testing for elevated levels of phenylpyruvate in the urine or phenylalanine in the blood.

    Alkaptonuria

    • A genetic disease that affects the breakdown of tyrosine and phenylalanine.
    • Caused by a lack of the enzyme homogentisate dioxygenase (HGD).
    • Homogentisic acid (HGA) builds up in the bones, cartilage, and urine.
    • Characterized by black urine, ochronosis (black bones and cartilage), and degenerative arthritis.

    Other Diseases of Amino Acid Metabolism

    • Cystinuria:
      • Defect in kidney transport of cysteine and basic amino acids.
      • Cysteine accumulates in the blood and oxidizes to cystine, forming calculi.
      • Treated by drinking large amounts of water or taking compounds that react with cysteine to form soluble derivatives.
    • Gyrate Atrophy:
      • Defect in ornithine transaminase activity.
      • Causes atrophy of the choroid and retina of the eyes.
      • Progress can be slowed by restricting dietary intake of arginine or administering pyridoxine.

    Fate of Carbon Skeletons After Removal of Nitrogen

    • Amino acids are degraded to pyruvate or citric acid cycle intermediates.
    • These intermediates can contribute to gluconeogenesis making them glucogenic.
    • Amino acids degraded to acetyl CoA or acetoacetate can contribute to the formation of fatty acids or ketone bodies, making them ketogenic.
    • Some amino acids are both glucogenic and ketogenic.

    Lysine Degradation

    • A ketogenic amino acid.
    • Saccharophine dehydrogenase (LYS1) is a key enzyme in this pathway.
    • Uses NADP+ and glutamate.

    Phenylalanine Degradation and Associated Clinical Implications

    • Phenylalanine is both glucogenic and ketogenic.
    • The enzyme phenylalanine hydroxylase is responsible for converting phenylalanine to tyrosine.
    • Phenylketonuria (PKU) is caused by a mutation in the gene encoding phenylalanine hydroxylase.
    • The disease is treated by dietary restriction of phenylalanine and supplementation with tyrosine.

    Nonketotic Hyperglycinemia (Glycine Encephalopathy)

    • Defects in the glycine cleavage enzyme complex lead to an accumulation of glycine in body fluids.
    • Causes severe mental deficiencies and often death in infancy.

    Amino Acids in the Body

    • Amino acids are used in the synthesis of important compounds.

    Heme Synthesis

    • Glycine and succinyl CoA are starting materials for heme synthesis.
    • Deficiencies of enzymes in the pathway can cause porphyrias.

    Creatine Synthesis

    • Creatine is synthesized from arginine and glycine.
    • Catabolic product of creatine is creatinine, excreted in urine.
    • Creatinine levels are used to assess renal function.

    Catecholamines Synthesis

    • Catecholamines are synthesized from phenylalanine and tyrosine.
    • Include dopamine, norepinephrine (noradrenalin), and epinephrine (adrenalin).

    Catecholamines Synthesis - Clinical Implications

    • Dopamine is a neurotransmitter involved in Parkinson's disease.
    • Melanin is derived from dopa and synthesized in melanocytes.
    • Defects in melanin synthesis result in albinism.

    Catecholamines Synthesis - Fight or Flight Hormones

    • Norepinephrine (noradrenalin) functions as a neurotransmitter in the brain.
    • Epinephrine (adrenalin) is a hormone produced in the adrenal glands and certain neurons.
    • Epinephrine plays a role in the fight-or-flight response.

    Tyrosine Metabolism Products

    • The thyroid gland produces iodinated derivatives of tyrosine: triiodothyronine (T3) and tetraiodothyronine (T4).

    Tryptophan Metabolism Products

    • The nicotinamide moiety of NAD(P) is derived from tryptophan.
    • Serotonin (5-hydroxytryptamine) is a neurotransmitter involved in smooth muscle contraction and vasoconstriction.
    • Melatonin is produced by the pineal gland and involved in daily and seasonal rhythms.

    Neurotransmitters from Glutamine

    • Brain neurons synthesize glutamate through hydrolysis of glutamine.
    • Glutamate is an excitatory neurotransmitter.
    • Glutamate is decarboxylated to produce γ-aminobutyric acid (GABA), an inhibitory neurotransmitter.

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    Description

    Test your knowledge on the metabolic disorders related to amino acids, including Phenylketonuria (PKU) and Alkaptonuria. This quiz covers the mechanisms, symptoms, and screening processes associated with these conditions. Perfect for students studying biochemistry or genetics!

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