lecture 24 - nitrogen - PoNF

what are the main nitrogen containing molecules of the body (3)

amino acids
nucleotides
proteins

dietary protein fate in stomach

enzymatically hydrolysed by pepsin in the stomach to peptides

dietary protein fate in in small intestine

trypsin and chymotrypsin cut proteins and larger peptides into smaller peptides
aminopeptidase and carboxypeptidase A and B degrade peptides into amino acids

Name the essential amino acids

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

PKU (phenylketonuria)

caused by lack of phenylalanine hydroxylase production
toxic build up of phenylalanine
autosomal recessive

function of urea cycle

remove excess nitrogen mostly from amino acids
converts excess ammonia into urea in liver cells

why convert ammonia to urea

ammonia is highly toxic and insoluble
urea is soluble and can be excreted in urine

Where does the urea cycle occur?

mainly in liver mitochondria and cytosol

simplified urea cycle

ammonia --> urea --> eliminated

what are the 2 steps before urea cycle

transamination

oxidative deamination

what process in the body forms ammonia

amino acid/protein break down

transamination

transfer of amino group

usually from alanine or a-ketoglutarate which will be converted to glutamate

oxidative deamination

glutamate is converted to a-ketoglutarate in liver by removal of amino group and releases ammonia

first reaction in urea cycle and where

NH3 + CO2 --> carbamoyl phosphate

hepatic mitochondria

carbamoyl reaction and where (step 2 urea cycle)

joins with ornithine to form citrulline which moves into cytosol
hepatic mitochondria

reaction of ornithine (step 3 urea cycle)

converted into arginosuccinate

what is arginosuccinate converted into (step 4 urea cycle)

arginine releasing fumarate to be used in citric acid cycle

final step in the urea cycle

arginine conversion to orthinine which releases urea

metabolic defects of urea cycle (enzyme that forms citrulline)

OTC deficience
hyperammonaemia, highly toxic
typically present from newborn period
x linked recessive