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26 Cards in this Set
- Front
- Back
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What are the only amino acids that escape liver degradation?
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LIV: (branch chain amino acids)
Leucine Isoleucine Valine |
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In general what is the first step of amino acid degradation? (p306) What are the two resulting products?
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Ammonia is transferred from an amino acid by aminotransferases to alpha-ketoglutarate from the citric acid cycle - produces alpha-ketoacid and glutamate.
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What is a required co-factor for aminotransferases? How does it work?
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Pyridoxal Phosphate (PLP, vitamin B6 derivative). This co-factor binds the amino acid through the amine group in an orientation that facilitates the removal of the amino group - most are specific to an amino acid.
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As you know from the phenylalanine catabolism pathway, one of the final products is Acetoacetyl-CoA. What are the potential fates of this product?
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TCA or FA synthesis using Citrate.
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Describe how LIV is degraded. First the two enzymes used and the final products. (p303)
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LIV are converted to alpha-keto acids using Branched-Chain Amino Transferases (Requiring PLP). The LIV alpha-keto acids are converted to Acyl-CoA derivatives via Branched-Chain alpha-keto acid dehydrogenases complex. Leucine produces Acetyl CoA and Acetoacetyl CoA. Isoleucine produces Succinyl CoA and Acetyl CoA. Valine produces Succinyl CoA.
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What disease is associated with a defect in the Branched-Chain aa pathway? (p.303)
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Maple Syrup urine disease is caused by a defect in the alpha-keto acid dehydrogenase complex.
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Why are aminotransferases used diagnostically? What are two examples? (p306)
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BC rarely are they found in the blood. Only when there is tissue damage is it found in the blood. ALT and AST are often used. Alanine Amino Transferase and Aspartate Amino Transferase.
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What are elevated ALT levels indicative of? Why?
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ALT levels are highest in liver cells, so if high levels are found in the blood, this suggests liver damage due to hepatitis, ischemia, toxicity, prolonged hypotension.
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What are elevated AST levels indicative of?
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Heart and kidney tissue damage.
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What's up with Dehydratases and Lyases in aa metabolism? What aa do the metabolize? (p307)
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These enzymes produce free ammonia. Dehydratase works with Serine and Threonine. Lyases work with Histidine.
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What three aa are used to transport free ammonia to the liver for conversion to urea? (p307)
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Sag:
Serine, Alanine, Glutamine |
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What is the major transporter of ammonia in extrahepatic tissues? (p.308)
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Glutamine
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Memorize the glutamine ammonia transfer pathway on p308
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Memorize the glutamine ammonia transfer pathway on p308
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What does the kidney and muscle use to transport free ammonia to the liver?
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Alanine
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As the liver processes ammonia to urea, in what form does it ammonia enter the mitochondria from the cytosol? (p309)
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In the form of Glutamine or Glutamate
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What molecules are used by the liver to produce urea? (p310)8
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Glutamine, glutamate, and free ammonia.
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What is the first step of the urea cycle starting with Glutamine? What does this rxn require?(p310)
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Glutaminase removes an ammonia from Gluamine (2 NH3) to make Glutamate (1 NH3). Rxn requires water.
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What is the first step of urea cycle starting with Glutamate? What does this reaction require? (p310)
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Glutamate Dehydrogenase removes an amino group from Glutamate to produce alpha-ketoglutarate.
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How is the Glutamate Dehydrogenase enzyme controlled? (p310)
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Via allosteric control by the cellular energy level. High ADP stimulates Glutamate Dehydrogenase. High GTP inhibits this enzyme.
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Once free NH4 is produced in the mitochondria, what happens? (p311)
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Carbamoyl Phosphate Synthetase I catalyzes the rxn between free NH4, bicarbonate and 2 ATP to form Carbamoyl Phosphate.
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What does the carbamoyl phosphate synthetase I enzyme require? (p311) What is this made from and how is its synthesis regulated?
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N-acetyl glutamate. Made from Glutamate and Acetyl CoA. The rxn is catalyzed by acetylglutamate synthase and it is controlled by Arginine.
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Glutamate is an precursor for which neurotransmitter for:
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gamma-aminobutyrate
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What is orotic aciduria? p316
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It is an accumulation of orotate in the urine due to an excess amount of Carbamoyl Phosphate. The carbamoyl-P accumulates bc the ornithine transcarbamylase is deficient and can't react carbamoyl-P with ornithine. Carbamoyl-P moves to the cytosol via mass action and feeds the pyrimidine pathway- of which orotate is an intermediate.
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What are the symptoms of Ornithin Transcarbamoylase Deficiency? What is the inheritance? (p316)
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1. Lethargy, apnea, bradycardia
2. Hyperammonemia 3. Hyperglutaminemia and hyperalaninemia 4. X-linked |
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How can deficiencies in Ornithine Transcarbamoylase deficiency be treated? What does this accomplish? (p317)
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Combination of Benzoate and Phenylacetate can be used. Benzoate is activated by dehydrognase to Benzoyl CoA which then reacts with Glycine - making Hippurate which is excreted.
Phenylacetate reacts with dehydrogenase, becoming an activated Pheylacetyl CoA - it reacts with Glutamine to become Phenylacetylglutamine that effectively removes 2 Ammonia's and is excreted. |
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Acetyl-CoA fuels the TCA cycle. What fuels the urea cycle?
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Carbamoyl Phosphate
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