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
What is a glucogenic amino acid?
One that can be used in gluconeogenesis
What is a ketogenic amino acid?
One that can be used in the production of lipids and ketone bodies
What are essential amino acids?
Ones that the organism cannot synthesise their own carbon skeletons for these, must obtain these in their diet
What are non-essential amino acids?
Ones where the organism can synthesise the alpha-keto analogue from essential AAs
