Nitrogen Metabolism and Fates of AAs Flashcards Preview

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Flashcards in Nitrogen Metabolism and Fates of AAs Deck (18)
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name the essential amino acids

  • phenylalalinee
  • valin
  • tryptophan
  • threonine
  • isoleucine
  • methionine
  • histidine
  • argigine (conditionally essential)
  • leucine
  • lysine


name the amino acids whose side chains are related to glycolysis or TCA intermediates

  • pyruvate = alanine
  • oxaloacetate = aspartate, asparagine
  • alpha-KG = glutamine


describe protein degradation pathways


describe the role of the liver in nitrogen metabolism

  • liver is the site where most of the amino acids release their amino groups as ammonia
    • NH3 is toxic
    • carbon skeleton is released
  • NH3 is detoxified to urea via the urea cycle in liver
  • urea is the major end-product of N metabolism
  • amino acid carbon skeletons are:
    • used for gluconeogenesis
    • burned in the TCA cycle


describe the role of kidney in nitrogen metabolism

  • urea formed in the liver is transported to the kidneys where it is excreted in the urine
  • kidneys also excrete ammonia as ammonium ions
    • regulation of acid base balance 
    • ammonia source is from glutamine (glutaminase enzyme)


_____ is the major nitrogen compound excreted in the urine

urea is the major nitrogen compound excreted in the urine



what are the 3 or 4 D's of pellagra

  • Diarrhea
  • Dermatitis
  • Dementia
  • (Death)


describe cystinuria

  • tubular reabsorption of cystine is decreased (along with dibasic AA ornithine, arginine, lysine) due to an inheretied deficiency of the cystine transporter
  • cystine is excreted in urine
  • cysteine tends to precipitate in the renal tubules (renal stones) in the renal tract


contrast the crystals seen in cystinuria with crystals seen in gout

  • cystinuria: hexagonal cysteine crystal
  • gout: birefringement crystals of sodium urate 


describe Hartnup disease

  • inherited defect in the transport of tryptophan
    • a neutral AA
  • decreased dietary absorption of tryptophan and increased excretion of tryptophan 
  • manifestations of tryptophan deficiency
    • may lead to NAD+ deficiency (pellagra)


describe why pellagra occurs in Hartnup disease


contrast glucogenic vs ketogenic amino acids

  • glucogenic: catabolism yields pyruvate or one of the intermediates of the citric acid cycle
    • substrates for gluconeogesis
  • ketogenic: yields acetoacetate, acetyl CoA or acetoacetyl CoA
    • not substrates for gluconeogenesis


which 2 amino acids are used in ketone body synthesis?

Lysine and leucine


describe alanine metabolism

  • alanine is the major transport form of amino acid from the muscle (important during starvation)
  • alanine (pyruvate) is the major precursor of gluconeogenesis during starvation
  • glucose-alanine cycle involves the muscle (where alanine is formed) and liver (site of gluconeogenesis)


describe the glucose-alanine cycle

  • pyruvate formed in the muscle by glycolysis is transaminated to alanine
  • alanine is transported to the liver and is coverted to glucose by gluconeogenesis


describe glutamate metabolism


describe aspartate metabolism