lecture 24 - nitrogen - PoNF

what are the main nitrogen containing molecules of the body

amino acids

nucleotides

proteins

dietary protein fate

proteins are enzymatically hydrolysed by pepsin in the stomach to peptides

trypsin and chymotrypsin in small intestine into smaller peptides

aminopeptidase and carboxypeptidase A and B degrade peprides into amino acids in small intestine

Name the essential amino acids

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

PKU

phenylketonuria

- caused by lack of phenylalanine hydroxylase production

- autosomal recessive

function of urea cycle

To remove excess nitrogen mostly from amino acids

- converts excess ammonia into urea in mitochondria of 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?

cytosol and mitochondria

what are the 2 steps before urea cycle

transamination

oxidative deamination

transamination

transfer of amino group

usually from alanine or alpha ketoglutarate which will be converted to glutamate

oxidative deamination

glutamte is converted to urea in liver by removal of amino group

formation of urea from urea cycle

- ammonia + carbon dioxide --> carbamoyl phosphate

- joins with citrulline which moves out of mitochondria into cytosol

- converted into arginosuccinate which is converted onto arginine releasing fumarate to be used in citric acid cycle

- arginine conversion to orthinine releases urea

metabolic defects of urea cycle

OTC deficiency

- hypeprammonaemia - highly toxic

- typically present from newborn period