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23 Cards in this Set
- Front
- Back
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Where does ammonia come from?
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- Transamination reactions of amino acids
- Dehydrate reactions of amino acids - Purine nucleotide cycle in brain and muscles - Amino acid deamidation reactions - Bacteria metabolism in gut |
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Where does the conversion from ammonia to urea occur?
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In the liver
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How is ammonia produced in muscle/peripheral tissues transferred to the liver?
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In the form of alanine (muscle only) or glutamine (muscle and peripheral tissue)
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What are the 5 enzymes involved in the conversion of ammonia to urea?
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1) Carbamoyl Phosphate Synthetase (CPS I)
2) Ornithin Transcarbamoylase (OTC) 3) Argininosuccinate synthetase (ASS) 4) Argininosuccinate lyase (ASL) 5) Arginase |
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What does Carbamoyl Phosphate Synthetase I (CPS I) do?
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- Bicarbonate + ammonia -> carbamoyl phosphate
- occurs in mitochondria - regulator step |
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What does Ornithin Transcarbamoylase (OTC) do?
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- Carbamoyl phosphate + ornithine -> citrulline
- occurs in mitochondria |
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What does Argininosuccinate synthetase (ASS) do?
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- Citrulline + aspartate -> argininosuccinate
- occurs in cytosol |
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What does Argininosuccinate lyase (ASL) do?
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- Argininosuccinate -> arginine + fumarate
- occurs in cytosol |
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What does Arginase do?
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- Arginine -> urea + ornithine (regenerated for the cycle)
- occurs in cytosol |
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How is CPSI regulated?
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- Increase in N-acetylglutamate (NAG) increases CPS1 activity
- NAG is positively regulated by increasing levels of glutamate and arginine |
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What are two enzymes that are checked for liver function?
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- Alanine Transaminase (ALT)
- Aspartate Transaminase (AST) |
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What enzymes are involved in the transfer a NH3 from an amino acid to an alpha-keto acid?
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- Transaminase
- PLP (Vitamin B6) |
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What is Encephalopathy?
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- Disease/disorder of the brain caused by high levels of ammonia
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What are causes of hyperammoniemia besides breakdown of the urea cycle?
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- Hepatitis
- Liver cirrhosis/carcinomas - Drugs (ie. valproate and 5-fluorouracil) |
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What are the mechanisms of hyperammonemia/ neurotoxicity?
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- NH4+ is similiar to K+ and blocks the K+ channels causing neural problems
- Osmolarity changes - Inhibition of neurotransmitter synthesis - Impaired oxidative phosphorylation |
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What are some treatments of hyperammonemia/ ammonia neurotoxicity?
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- IV phenylacetate/benzoate for acute disorder
- Hemodialysis for acute - Antibiotics to decreases NH4+ production from gut bacteria - Administer urea cycle intermediates - Decrease protein in diet - Na phenylbutarate and Na benzoate to neutralize and facilitate secretion |
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Symptoms of Hyperammonemia/ ammonia neurotoxicity
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- Lethargy, vomiting, ataxia, seizures, coma, death, excreting urea cycle intermediates
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Hyperammonemia Type I
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- Deficient CPSI
- Low orotate, citrulline, arginine - High ammonia - Glutamine in urine - Located in mitochondria |
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N-acetylglutamate synthase deficiency (NAGS)
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- Deficient NAGS (regulates CPSI)
- Glutamine in urine - Located in mitochondria |
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Hyperammonemia Type II
( OTC deficiency ) |
- Deficient OTC
- High Orotate and ammonia - Low Citrulline and arginine - Glutamine and Orotic acid in urine - located in mitochondria |
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Citrullinemia
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- Deficient ASS
- High Citrulline and ammonia - Low arginine - Citrulline in urine - located in cytosol - Located in cytoplasm |
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Argininosuccinic-aciduria
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- Deficient ASL
- High Citrulline and ammonia - Low Arginine - Arginosuccinate in urine - located in cytosol |
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Argininemia
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- Deficient Arginase
- High Arginine and ammonia - Arginine, Lysine, and cysteine in urine - Located in cytosol |
