Amino Acids, Proteins and Porphyrins
Which one of the following statements is correct?
|A||An increase in gluconeogenesis from amino acids results in a decrease in urea formation.|
|B||All essential amino acids are glycogenic.|
|C||Ornithine and citrulline are found in tissue proteins.|
|D||Cysteine is an essential amino acid in individuals consuming a diet severely limited in methionine.|
a. Methionine is the precursor of cysteine. An increase in gluconeogenesis releases increased ammonia and results in increased urea production.
b. The essential amino acids leucine and lysine are ketogenic. Ornithine and citrulline are amino acids that are intermediates in the urea cycle, but are not found in tissue proteins. Phenylalanine is essential regardless of the level of tyrosine.