Nitrogen Metabolism Flashcards
(22 cards)
What are ureotelic organisms?
Terrestrial vertebrates that excrete urea
What are uricotelic organisms?
Birds and reptiles that excrete uric acid
What are ammonetelic organisms?
Aquatic animals that excrete ammonium
What happens to amino groups during protein catabolism?
They are removed through deamination and the carbon skeletons are degraded into metabolic intermediates
What enzyme catalyses the transfer of amino groups in oxidative deamination?
Transaminases
What reaction is catalysed by aspartate aminotransferase?
Aspartate + α-ketoglutarate ↔ oxaloacetate + glutamate
What enzyme removes ammonium ions from glutamate?
Glutamate dehydrogenase
Why is ammonia toxic to the body?
- It freely crosses membranes
- Disrupts the citric acid cycle
- Alters neural osmotic balance
What happens when ammonia diffuses into mitochondria?
It is converted to NH4+ and inhibits the proton gradient needed for oxidative phosphorylation
What is the overall role of the urea cycle?
To convert toxic ammonia into less toxic urea for excretion
What are the two major nitrogen sources entering the urea cycle?
- Free ammonia
- Amino group from aspartate
What two enzymes are involved in transferring nitrogen to the urea cycle?
- Glutamate dehydrogenase
- Aspartate transaminase
How much energy is required for urea synthesis?
4 high energy phosphate groups from 3 ATP molecules
How are ATP molecules used in the urea cycle?
- Two ATPs used for carbamoyl phosphate formation
- One ATP for argininosuccinate formation
How do ruminants utilise urea differently compared to non-ruminants?
They secrete urea into the rumen where microorganisms use it to synthesise amino acids
How do animals like camels conserve water during nitrogen excretion?
They avoid water loss by recycling urea internally instead of excreting it
What is citrullinaemia and which animals are affected?
A genetic defect of Holstein-Friesian calves cause by argininosuccinate synthetase deficiency leading to ammonia poisoning
What are clinical signs of citrullinaemia in calves?
- Depression
- Tongue protrusion
- Unsteady gait
- Frothing at the mouth
What causes the disruption of the urea cycle in citrullinaemia?
A single base substitution mutation in the argininosuccinate synthetase gene
What is the final nitrogenous waste product in ureotelic organisms?
Urea
What is the final nitrogenous waste product in uricotelic organisms?
Uric acid
What is the final nitrogenous waste product in ammonetelic organisms?
Ammonium
