unwanted amino acids are converted into urea in the liver.
unwanted amino acids are converted into urea in the liver.
where are unwanted amino acids converted into urea?
liver
amino acids from ingested food that are not used for the synthesis of proteins and other biological substances — or produced from catabolism of muscle protein — are oxidized by the body as an alternative source of energy, yielding urea and carbon dioxide. the oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is then fed into the urea cycle. the first step in the conversion of amino acids from protein into metabolic waste in the liver is removal of the alpha-amino nitrogen, which results in ammonia. because ammonia is toxic, it is excreted immediately by fish, converted into uric acid by birds, and converted into urea by mammals.
urea
when taken up into the human body from the diet, the 20 standard amino acids either are used to synthesize proteins, other biomolecules, or are oxidized to urea and carbon dioxide as a source of energy. the oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is then fed into the urea cycle. the other product of transamidation is a keto acid that enters the citric acid cycle. glucogenic amino acids can also be converted into glucose, through gluconeogenesis. of the 20 standard amino acids, nine (his, ile, leu, lys, met, phe, thr, trp and val) are called essential amino acids because the human body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food. in addition, cysteine, taurine, tyrosine, and arginine are considered semiessential amino-acids in children (though taurine is not technically an amino acid), because the metabolic pathways that synthesize these amino acids are not fully developed. the amounts required also depend on the age and health of the individual, so it is hard to make general statements about the dietary requirement for some amino acids. dietary exposure to the non-standard amino acid bmaa has been linked to human neurodegenerative diseases, including als.
amino acid