PoH: Nitrogen Flashcards
What two molecules in the body contain nitrogen?
Amino acids and nucleotides
How many AAs are there?
20 (around 20)
What’s an essential AA and how many are essential?
An AA we can’t synthesise in the body (in sufficient quantity) so we must get it from our diet
There’s 9 essential AAs
What’s a conditionally essential AA?
AA required to some degree in young, growing and/or sometimes during illness
What mnemonic is used to remember essential AAa?
PVT TIM HALL
Phenylalanine
Valine
Trytophan
Threonine
Isolucine
Methoinine
Histadine
(Arginine)
Lysine
Leucine
During N metabolism, AAs can become carbon skeletons (deaminated AAs). What happens to them next?
We use them to form glucose or fats, or if we’re hungry, convert them to a metabolic intermediate that can be oxidised by the citric acid cycle
N metabolism features 3 potential cycles. What are they?
Urea cycle
Aspartate-arginino-succinate shunt of citric acid cycle
Citric acid cycle
Describe the fate of dietary protein
They’re enzymatically hydroysed by
Pepsin in the stomach
Trypsin and chymotrypsin in the SI
Aminopeptidase and carboxypeptidases A and B in the SI
What’s the aim of the urea cycle
To take toxic ammonia and turn it into harmless urea - ridding the body of excess nitrogen
Where does the urea cycle take place
Mitochondria and cytoplasm
The body catalyses proteins that are… (4 things)
From the diet
Misfolded
Foreign
Unwanted
How is protein catalysed?
It’s turned into proteasomes
Then peptide fragments
Proteolysis breaks them into amino acids
What causes PKU?
Normally, phenylalanine is converted to tyrosine by enzyme phenylalanine hydrogase
In PKU there’s an absence of the enzyme. Substrates are instead converted to toxic products which can cross the blood-brain barrier and cause irreversible damage
Explain screening for PKU
Infants are screened via a heel-prick “Guthrie Card” test on Day 5
How is PKU treated?
It’s treated by reducing protein in the diet and supplementing tyrosine. They’re then monitored through blood tests.
Define metabolic disorders relating to urea cycle and give 2 examples
Caused by any step in the urea cycle not functioning properly. The faulty step can be identified by systematically testing concentrations of molecules in the pathway and finding which levels are too high and which levels are too low
PKU
Ornithine transcarbonmoylase (OTC) deficiency
Symptoms of OTC deficiency and # who have it
Hyperammonaemia which is toxic. It’s most often noticed in babies who suffer from seizures where blood tests show high ammonia levels. Around 1 in 40,000 have it.
Define transamination
moving amino groups (NH2) from one AA to another AA, to make a new AA and alpha-keto acid. Glutamate is both a donor and an acceptor of amino groups.
Describe the role of glutamate in transfer of nitrogen to, from and between amino acids.
Glutamate is central to nitrogen entering the body.
Once it is broken down, the nitrogen from those amino acids is transferred (transaminated) to alpha-ketoglutarate to form glutamate.
Glutamate is then used as an amino group donor for the synthesis of non-essential amino acids.
What’s special about glutamate
Glutamate helps N get into body. It’s a precursor in the biosynthesis of other AAs like proline, arginine and histidine
How is N transported through plasma to the liver?
- We eat N
- The GI tract catabolises it to AAs
- AAs are absorbed into bloodstream
- Cells take AAs
- Cells leave toxic ammonia
- Ammonia goes into bloodstream
- Liver converts ammonia to urea via urea cycle
