Lecture 7 - Nitrogen Metabolism Part 3 Flashcards
what is the main carrier of nitrogen from muscle to liver
alanine
why must ammonia levels stay low
it is toxic, especially for the brain
where is urea synthesised
in the liver
the liver will take up excess NH3 in the form of what
alanine and glutamine
how and where is urea transported to for excretion
transported in the blood to the kidneys for excretion
how does urea reduce the toxicity cause by ammonia
it maintains N in a soluble, non toxic form
(urea = non toxic, ammonia = toxic)
what are the two ways that nitrogen enters the urea cycle
carbamoyl phosphate and aspartate
what is carbamoyl phosphate is synthesised from
synthesised from bicarbonate and ammonia
what does ammonia come from
the deamination of glutamine and glutamate
what kind of reaction forms carbamoyl phosphate and what is it catalysed by
Energy requiring reaction catalysed by carbamoyl phosphate synthetase
what is aspartate generated by
transamination
where is oxaloacetate formed that is used to produce aspartate
in the citric acid cycle
where do the first two reactions of the urea cycle occur
in the mitochondria
where do the rest of the reactions apart from the first two of the urea cycle occur
in the cytosol
where is arginine made
in the urea cycle, it is the non essential and essential amino acid
what is the major point of regulation of the urea cycle
carbamoyl phosphate synthetase (CPS) activity
when is carbamoyl phosphate synthetase (CPS) activity upregulated
under conditions of high protein diet or early stages of fasting / starvation
when can urea cycle activity by reduced
liver disease e.g cirrhosis
how is carbamoyl phosphate synthetase regulated and what does this mean
allosterically regulated
- the activity of the enzyme is regulated by the binding of a molecule to the enzyme that is not the active site
what is the allosteric regulator that binds to carbamoyl phosphate synthetase to activate it
N - acetylglutamate
in what situations will N - acetylglutamate be made
situations of high glutamate and Acetyl-CoA
what are the phenotypes of disorders to the urea cycle
Variety of phenotypes (mainly neurological - brain issues and all involve hyperammonemia)
how to treat disorders of the urea cycle enzymes
- by dietary modification i.e limit the protein in the presence of sufficient calories
- With amino acid-binding compounds i.e. phenylbutyrate
what does a defect to an enzyme in the urea cycle cause
- build up of ammonia, which is very toxic
- high levels of ammonia found in the blood leads to brain issues and lethargicness
can defects to the urea cycle enzymes be inherited
yes
what enzyme is the most common to have a defect in the urea cycle
OTC
what gender is a defect to OTC more likely in and why
more likely in males because it is on X chromosome
in the brain what may NH4+ inhibit
post synaptic potentials
what does depletion of citric acid cycle intermediates mean for the brain
decreased ATP for brain function
accumulation of glutamine in astrocytes causes what and why
increases osmotic pressure cerebral oedema
- as glutamine is osmotic type compound, water will follow it and can cause swelling in the brain)
how does phenylbutyrate assist the clearance of nitrogen waste
the drug is rapidly converted to phenylacetate, which combines with glutamine to form phenylacetylglutamine
this contains two nitrogen atoms and is excreted so increases the clearance of nitrogen waste
how is NH4+ produced in the kidneys
by deamination of glutamine
in the process of ammonia being excreted into urine, ammonia is released in the epithelial cell in what form and what from
ammonia is released in the protonated form from glutamine and glutamate
before NH4+ is pumped from the epithelial cell into the lumen what happens to it
proton is split from NH4+ to form NH3
what allows NH3 to be pumped into the lumen and enter the urine
The sodium proton exchange allows protons to be pumped into the lumen
the kidney can utilise a-ketoglutarate to produce what
produce glucose
