The determination of the base sequence of a nucleic acid is much more difficult than the determination of the sequence of amino acids of a protein, because there are only 4 types of monomers instead of 20. This explains why one began with the determination of the sequences of transfer ribonucleic acids (more than 200 sequences are known); these do [...]
It is not surprising that the metabolism of these two aromatic amino acids is closely linked because they differ only by the presence of a phenolic OH in the tyrosine molecule. We will not study here their biosynthesis which — in organisms where it takes place, especially bacteria — starts from 2 compounds of the carbohydrate metabolism (erythrose-4-℗ and phosphocnolpyruvate) [...]
We have seen that some amino acids are utilized by the animal organism as detoxication agents and that products like benzoyl-glycine (hippuric acid) or phenyl-acetyl-glutamine can be found in urine. We will also see that urobilin and stercobilin, the degradation products of hemoglobin (see fig. 7-33), are present in faeces. But generally, nitrogen is eliminated in 3 forms: 1. Ammonia [...]