Urea cycle

what is the main purpose of the urea cycle?

to convert toxic ammonia into urea for safe excretion

Where does the urea cycle primarily occur?

in the liver

how many ATP molecules are required for one complete urea cycle?

4 high energy phosphates are cleaved

what is the primary form of amino acid group transport to the liver?

glutamine

what is the role of n-acetylglutamate in the urea cycle?

it allosterically activates carbamoyl phosphate synthetase 1

how does the urea cycle connect to the citric acid cycle?

Through aspartate-argininosuccinate shunt, converting oxaloacetate to fumarate

how many atp molecules are used in the argininosuccinate synthetase reaction?

two high energy phosphates

what is the key characteristic of transamination reactions?

substrates bind independently (not simultaneously)

What happens in the argininosuccinate synthetase step?

ATP is used to form agininosuccinate from citrulline and aspartate

how does the respiratory chain use NADH from the urea cycle?

it translocated protons across the inner mitochondrial membrane

what is the significance of fumarate production in the urea cycle?

its a product that links it to the citric acid cycle

what happens when glutamate dehydrogenase can’t bind gtp?

it results in elevated ammonia levels

how is ornithine transcarbamylase deficiency diagnosed?

by detecting 1mM orotic acid in the urine

what is the mechanism of benzoate treatment?

it consumes glycine to help control ammonia levels

what generates extra ATP in the linked urea-citric acid cycles?

the nadh produced leads to 2.5 atp via the respiratory chain

how does protein intake affect the urea cycle?

high protein increases enzyme synthesis and cycle activity

what role does aspartate play in the urea cycle?

it provides the second nitrogen for urea formation

what are the main symptoms of urea cycle disorders?

anorexia, vomiting and lethargy due to ammonia accumulation

why can’t patients with urea cycle disorders eat high protein diets?

they cannot properly process the ammonia produced from amino acid breakdown

what is the role of arginine supplementation in treatment?

it helps treat OTCD, ASD and ASLD deficiencies

what is the krebs bicycle?

interconnected urea and citric acid cycles

how does starvation affect the urea cycle?

increases activity due to breakdown of muscle protein

what role does carbamoyl phosphate synthetase 1 play?

it’s the first and rate-limiting enzyme of the urea cycle

Why isn’t a protein free diet a treatment option?

humans cannot synthesise nine essential amino acids

what is the role of glycine synthase in ammonia removal?

it consumes ammonia to produce glycine from CO2 and methylene tetrahydrofolate

what metabolite accumulates in ornithine transcarbamylase deficiency?

orotic acid, which is excreted in the urine