Biochemistry · MU Sofia

35.Detoxification Ammonia

Explains why ammonia is toxic to the central nervous system and how the liver detoxifies it, mainly through the urea cycle in periportal hepatocytes. Covers the cycle's intermediates, glutamine synthesis as an ammonia carrier, the glucose-alanine cycle linking muscle to liver, and the links to the citric acid cycle. Ends with an overview of urea cycle disorders and their enzyme deficiencies, plus four multiple-choice questions with answers.

Inside: 15 sections · 8 labelled pictures · 10 flashcards · 4 min

Topic 35 of 70 in the MU Sofia syllabus for Biochemistry (Dental Medicine, Year 2). The free AceMed note covers it in 14 sections, about 538 words (4 min of reading), with 10 flashcards.

In this note

  1. DETOXIFICATION OF AMMONIA
  2. UREA CYCLE:
  3. Urea Cycle
  4. Enzymes
  5. &
  6. Steps
  7. GLUTAMINE SYNTHESIS:
  8. SYNTHESIS OF GLUTAMATE AND GLUTAMINE
  9. UREA CYCLE AND AMMONIAGENESIS
  10. LINKS TO CITRIC ACID CYCLE
  11. GLUCOSE-ALANINE CYCLE
  12. ENZYME DEFECTS
  13. MCQS
  14. ANSWERS

DETOXIFICATION OF AMMONIA

  • Ammonia is highly toxic, particularly to the central nervous system, where it can lead to encephalopathy and coma.
  • In the liver, excess ammonia is detoxified to prevent such toxicity.
  • The urea cycle is the primary pathway for ammonia detoxification.

UREA CYCLE:

  • It occurs mainly in the liver's periportal hepatocytes (the regions surrounding the hepatic arteries and portal veins).
  • The cycle involves five enzymatic reactions that convert two molecules of ammonia and one molecule of carbon dioxide into one molecule of urea and one molecule of ornithine.
  • The urea produced is then excreted via the kidneys in urine.

GLUTAMINE SYNTHESIS:

  • Glutamine synthetase catalyzes the reaction between glutamate and ammonia to produce glutamine.
  • Glutamine serves as a transport form of ammonia, carrying it safely to the kidneys for excretion or to other tissues for use in biosynthesis.

SYNTHESIS OF GLUTAMATE AND GLUTAMINE

Glutamate Synthesis:

  • Glutamate is a non-essential amino acid synthesized from α-ketoglutarate, an intermediate of the citric acid cycle.
  • Glutamate dehydrogenase catalyzes the reversible conversion of α-ketoglutarate and ammonia to glutamate.
  • Glutamate is a central molecule in amino acid metabolism, serving as a precursor for the synthesis of other amino acids and as a neurotransmitter.

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