Biochemistry Lecture 12: Amino Acids Conversion
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Questions and Answers

What is the function of glucuronyl transferase enzyme in the hepatocyte?

  • To break down hydrogen peroxide in the RBCs
  • To synthesize creatine phosphate in muscles
  • To convert conjugated bilirubin to urobilinogen
  • To attach glucuronic acid to bilirubin, forming conjugated bilirubin (correct)
  • What is the main function of glutathione in the body?

  • To provide defense mechanism against certain toxic compounds (correct)
  • To activate some enzymes and inactivate insulin hormone
  • To absorb amino acids in the gut
  • To synthesize creatine phosphate in muscles
  • What is the product of glucuronic acid attachment to bilirubin?

  • Urobilin
  • Urobilinogen
  • Stercobilin
  • Conjugated Bilirubin (correct)
  • What is the main site of creatine synthesis?

    <p>Kidney, liver, and pancreas</p> Signup and view all the answers

    What is the function of glutathione in RBCs?

    <p>To break down hydrogen peroxide and prevent hemolysis</p> Signup and view all the answers

    What is the fate of majority of urobilinogen?

    <p>Excreted with the feces</p> Signup and view all the answers

    What is the structure of glutathione?

    <p>A tripeptide formed of three amino acids</p> Signup and view all the answers

    What is the role of creatine phosphate in muscles?

    <p>To store high energy phosphate and provide phosphate to ADP to form ATP during muscle exercise</p> Signup and view all the answers

    What is the function of creatine phosphate in muscles?

    <p>Not mentioned in the content</p> Signup and view all the answers

    What is the function of creatine kinase enzyme?

    <p>To catalyze the formation of creatine phosphate</p> Signup and view all the answers

    Which isoenzyme of creatine kinase is mainly found in heart muscle?

    <p>CK-MB</p> Signup and view all the answers

    What is the end product of creatine metabolism?

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

    What is the normal range of plasma creatinine?

    <p>0.6 - 1.4 mg/dl</p> Signup and view all the answers

    What is the precursor for Tyrosine in the liver?

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

    What is the deficiency of phenylalanine hydroxylase enzyme?

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

    What is the characteristic sign of Phenylketonuria?

    <p>Mental retardation</p> Signup and view all the answers

    What is the primary method for diagnosing phenylketonuria in infants?

    <p>Measuring blood phenylalanine levels using a Guthrie test</p> Signup and view all the answers

    Which of the following conditions is characterized by a deficiency of homogentisate oxidase enzyme?

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

    What is the primary treatment for hereditary tyrosinemia?

    <p>Feeding a diet low in tyrosine and phenylalanine</p> Signup and view all the answers

    Which of the following is a common consequence of alkaptonuria?

    <p>Generalized pigmentation of connective tissues</p> Signup and view all the answers

    What is the approximate frequency of phenylketonuria in live births?

    <p>1 in 10,000</p> Signup and view all the answers

    What is the recommended duration for dietary restrictions in individuals diagnosed with phenylketonuria?

    <p>Until the age of 6 years</p> Signup and view all the answers

    Which of the following enzymes is deficient in albinism?

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

    What is the primary characteristic of acute hereditary tyrosinemia?

    <p>Failure to thrive and liver failure</p> Signup and view all the answers

    What physiological function is associated with glycine?

    <p>Precursor for collagen and bile salts</p> Signup and view all the answers

    What is the first product formed when glycine reacts with Succinyl CoA?

    <p>Amino levulonic acid (ALA)</p> Signup and view all the answers

    How much bilirubin is produced daily from the degradation of hemoglobin in adults?

    <p>250–400 mg</p> Signup and view all the answers

    What percentage of bilirubin is derived from hepatic turnover of hem proteins?

    <p>20-25%</p> Signup and view all the answers

    What is biliverdin converted to during the degradation of heme?

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

    Which of the following proteins bind unconjugated bilirubin in the liver?

    <p>Cytosolic Y protein and cytosolic Z protein</p> Signup and view all the answers

    What happens to released iron after the oxidation of heme?

    <p>It's recycled</p> Signup and view all the answers

    What is the lifespan of red blood cells in the human body?

    <p>120 days</p> Signup and view all the answers

    Study Notes

    Conversion of Amino Acids to Specialized Products

    • Glycine is a non-essential glucogenic amino acid that serves as a precursor for various nitrogen-containing compounds.
    • Glycine is converted to:
    • Haeme (combines with globin protein to form hemoglobin)
    • Hippuric acid
    • Glutathione
    • Glyoxylic acid
    • Purine bases
    • Bile salts
    • Collagen
    • Creatine
    • Serine
    • Neurotransmitter

    Haeme Metabolism

    • Haeme is degraded to bilirubin, which is produced daily in adults (250-400 mg).
    • 70-80% of bilirubin comes from degradation of haemoglobin, while 20-25% comes from hepatic turnover of haem proteins.
    • The life span of red blood cells is approximately 120 days.
    • Senescent red blood cells are phagocytosed by cells of the reticuloendothelial system (spleen and liver).
    • Haem is oxidized by the haem oxygenase system, releasing ferric iron (Fe3+) and carbon monoxide (CO).
    • Biliverdin is reduced to bilirubin by biliverdin reductase.
    • Unconjugated bilirubin is transported to the liver, where it is bound to albumin and then conjugated with glucuronic acid.
    • Conjugated bilirubin is water-soluble and travels down the GI tract.

    Glutathione

    • Glutathione is a tripeptide formed from glutamate, cysteine, and glycine.
    • It exists in two forms: reduced (G-SH) and oxidized (G-SS-G).
    • Functions of glutathione include:
    • Defense against toxic compounds (detoxification)
    • Absorption of amino acids
    • Protection against cell damage and hemolysis of RBCs
    • Activation of some enzymes
    • Inactivation of insulin hormone

    Creatine

    • Creatine is synthesized from glycine, arginine, and methionine in the kidney, liver, and pancreas.
    • Functions of creatine:
    • Creatine is phosphorylated to creatine phosphate in muscles.
    • Creatine phosphate acts as a store of high-energy phosphate in muscles and is used during muscle exercise.
    • Creatine kinase enzyme (CK) catalyzes the formation of creatine phosphate.
    • There are three isoenzymes of CK: CK-MM (skeletal muscles), CK-MB (heart muscle), and CK-BB (brain).
    • Creatine phosphate is degraded to creatinine, which is excreted by the kidney in urine.
    • Diagnostic importance of creatinine:
    • Estimation of plasma creatinine is used as a kidney function test.
    • High blood creatinine and urea levels are sensitive indicators of renal failure.

    Phenylalanine Metabolism

    • Phenylalanine is a ketogenic and glucogenic essential amino acid.
    • Functions of phenylalanine:
    • Precursor for tyrosine in the liver
    • Deficiency of phenylalanine hydroxylase enzyme or dihydrobiopterin reductase results in phenylketonuria (PKU).
    • Effects of PKU:
    • Mental retardation
    • Increased blood phenylalanine
    • Failure to walk and talk
    • Hyperactivity and tremors
    • Failure to grow
    • Skin lesions (eczema)
    • Frequency of PKU: 1 in 10,000 live births
    • Diagnosis of PKU: measurement of blood phenylalanine by the Guthrie test in infants at 4 days old
    • Prevention of PKU: feeding infants with PKU a diet containing very low levels of phenylalanine

    Hereditary Tyrosinemia (Tyrosinosis)

    • Definition: inability to metabolize tyrosine and p-hydroxyphenylpyruvate
    • Cause: deficiency of tyrosine α-Ketoglutarate transaminase and p-hydroxyphenylpyruvate oxidase enzymes
    • Forms of tyrosinemia: acute (death from liver failure within 7 months) and chronic (liver cirrhosis and hepatic carcinoma, mild mental retardation)
    • Prevention and treatment: feeding a diet containing very low levels of tyrosine and phenylalanine

    Alkaptonuria

    • Definition: benign disease resulting from deficiency of homogentisate oxidase enzyme
    • Effects:
    • Deposition in joints causing arthritis
    • Deposition in connective tissue causing generalized pigmentation
    • Excretion in large amounts in urine, which is oxidized in the air giving dark urine

    Albinism

    • Definition: hereditary deficiency of tyrosine hydroxylase enzyme in melanocytes
    • Effects: defective synthesis of melanin pigments, affecting the eyes, skin, and hair
    • Types of albinism:
    • Ocular albinism
    • Cutaneous albinism

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    Description

    This quiz covers the conversion of amino acids to specialized products, including glycine's role in producing haeme, hippuric acid, and other compounds with physiological functions.

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