Urea and nitrogen cycle Flashcards
What is the function of the urea cycle?
Remove ammonia from the body
Why is the urea cycle necessary?
- Amino acids cannot be stored as amino acids
- Deamination of AAs produces ammonium and alpha-ketoacids
- Ammonium toxic and so needs to be removed
List the subgroups produced by amino acid deamination
- Amine subgroup
- Alpha-ketoacids
What happens to the amine group in most land animals?
- Either used to resynthesise AAs
- Or feed urea cycle and be excreted
What happens to the alpha-ketoacids?
Go into Krebs cycle
What is the difference between the urea and krebs cycle of most land animals and birds/reptiles?
- In land animals are linked
- In birds and reptiles are unlinked
What are ammonotelic animals?
- Easily synthesise and excrete ammonium
- Fish
- Ammonium synthesised in the liver
- Excretion via the gills
Describe ureotelic animals
- Excretion of urea
- Most land animals
- Synthesised in liver
- Transported via blood to kidney
- Excretion through bladder/urethra
Describe uricotelic animals
- Excrete uric acid
- Birds/reptiles
- Synthesised in liver
- Transported via blood to kidney
- Excretion through the cloaca
What are the 2 pathways that lead to excess nitrogenous compounds in the body?
- Diet proteins digested/broken down
- Breakdown of skeletal muscle proteins (starvation)
Describe the process of deamination
- alpha-amino acid and alpha-ketoglutarate react via transaminase to form alpha-ketoacid and glutamate
- Glutamate reacts with NAD and H2O via glutamate dehydrogenase to form alpha-ketoglutarate and NADH and ammonium
How can excess ammonium be removed in the absence of amino acids?
Formation of glutamate adn glutamine
Describe the fate of alpha-ketoa acids
- Fate of these carbonated cytoskeletons directly related to their structure
- 20 different pathways, all converge to 7 common metabolic intermediates the feed TCA cycle
Describe the urea cycle
- 2ATP +bicarbonate +ammonia to carbomyl phosphate via carbomyl synthetase
- Carbomoyl phosphate and ornithine to citrulline via ornithine transcarbomoylase
- Citrulline to arginino succinate via ATP
- Arginino succinate to fumarate and arginie via arginosuccinase
- Arginine to ornithine via arginase
Describe the urea cycle in birds
- Glutamine into glutamate and phosphoribosylamine
- Phosphoribosylamine to phosphoribosylglycineamide via glycine
- Then to phosphoribosyl-N-formylglycineamide
- Then to phosphoribosyl-5-aminoimizadole-4-carboxylate via glutamate
- Then to inosine monophosphate via aspartate
- Then to xanthine (and to uric acid) and 5-PRPP
