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OVERVIEW OF AMINO ACID METABOLISM

OVERVIEW OF AMINO ACID METABOLISM. ENVIRONMENT ORGANISM. Bio- synthesis. Protein. Ingested protein. 2. 3. 1. a. AMINO ACIDS. b. c. Degradation (required). c. Purines Pyrimidines Porphyrins. Nitrogen. Carbon skeletons.

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OVERVIEW OF AMINO ACID METABOLISM

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  1. OVERVIEW OF AMINO ACID METABOLISM ENVIRONMENT ORGANISM Bio- synthesis Protein Ingested protein 2 3 1 a AMINO ACIDS b c Degradation (required) c Purines Pyrimidines Porphyrins Nitrogen Carbon skeletons Urea (ketogenic) (glucogenic) pyruvate α-ketoglutarate succinyl-CoA fumarate oxaloacetate Used for energy acetoacetate acetyl CoA

  2. NITROGEN BALANCE Nitrogen balance = nitrogen ingested - nitrogen excreted (primarily as protein) (primarily as urea) Nitrogen balance = 0 (nitrogen equilibrium) protein synthesis = protein degradation Positive nitrogen balance protein synthesis > protein degradation Negative nitrogen balance protein synthesis < protein degradation

  3. TRANSAMINATION

  4. UREA CYCLE mitochondria cytosol Function: detoxification of ammonia (prevents hyperammonemia)

  5. FATE OF THE CARBON SKELETONS Carbon skeletons are used for energy. Glucogenic: TCA cycle intermediates or pyruvate (gluconeogensis) Ketogenic: acetyl CoA, acetoacetyl CoA, or acetoacetate

  6. Purine and Pyrimidine Metabolism

  7. Major Bases

  8. Source of each atom in the purine ring

  9. Ribose-5-phosphate 5-Phosphoribosyl-1-pyrophosphate (PRPP) ⊖ ⊕ ⊖ ⊖ 5-Phosphoribosylamine IMP ⊖ ⊖ Adenylosuccinate XMP GMP AMP Summary and Regulation

  10. Inhibition of Purine Biosynthesis by the Antitumor Agent, 6-Mercaptopurine • 6-Mercaptopurine is converted to a nucleotide. • The nucleotide inhibits purine biosynthesis at steps 2, 12a, 12b, and 13a.

  11. Cytosine (C) Uracil (U) Thymine (T) Major Bases

  12. Sources of the atoms of the pyrimidine ring:

  13. DNA and RNA Degradation

  14. “Salvage Pathway” for Purines (~90%) Lesch-Nyhan Syndrome

  15. Degradation of Purines (~10%)

  16. Allopurinol Inhibits xanthine oxidase X X

  17. Heme

  18. Structure

  19. Porphyrias

  20. hemoglobin globin heme Fe (reutilized) degraded (bilirubin) free amino acids

  21. Heme Biliverdin Unconjugated bilirubin Reticuloendothelial system Unconj.bilirubin/albumin complex Systemic circulation Kidney Unconj. bilirubin Bilirubin diglucuronide Hepatocytes urine Bilirubin diglucuronide Urobilinogen Bilirubin Stercobilins Small intestine Large intestine

  22. HYPERBILIRUBINEMIA -- elevated bilirubin in serum (above 1 mg/dL) -- can be conjugated or unconjugated or both depending on the situation -- elevated bilirubin can diffuse into tissues, making them appear yellow (jaundice)

  23. bilirubin encephalopathy (kernicterus) HYPERBILIRUBINEMIA Clinical Consequences: -- Conjugated hyperbilirubinemia: benign -- Unconjugated hyperbilirubinemia: benign at concentrations < 25 mg/dL (albumin capacity) -- At concentrations >25 mg/dL, unconjugated bilirubin is free (uncomplexed) and can enter the brain.

  24. Causes of JAUNDICE • Hemolytic anemia • --  destruction of erythrocytes • Hepatitis or cirrhosis • --  conjugation and excretion of bilirubin • Bile duct obstruction • -- conjugated bilirubin not delivered to intestine; • it backs up, spills over into the blood • Neonatal “physiological jaundice” • -- immature hepatic system of the newborn: •  uptake, conjugation, excretion of bilirubin

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