Mechanism of the synthesis. Regulation of protein synthesis is, then, to put the particular ammoacid

physiology, gout Hurine (adeinne and guanine) and pyrimidine (cytosibine, thymine and uracil) bases, can be obtained as a breakdown product of cellular DNA or RNA, or they may be obtained from ingested food nucleic acids. These bases can also be synthesized in the body. Daily breakdown ot large number of cells which occur normally, provide a large amount of purine and pyrimidme bases to our body, which must be disposed. The food contains variable amounts of nucleic acid. Highly cellular foods like liver, kidney and pancreas are rich in nucleic acids, hence purine and pyrimidme bases. Besides, tea coffee and cocoa contain some purme bodies (caffeine and theobromine). Pancreatic juice contains nucleotidases and nucleosidases. Nucleotidase splits nucleotides into nucleosides and phosphoric acid. Nucleosidase breaks nucleosides into the nitrogenous base and pentose sugar. The purme and pyrimidme bases can also be synthesized in our body This has been proved variously. Thus a baby animal rared on purme free food continues to grow and synthesize DNA and RNA molecules Purine is synthesized from formyl derivative of tetrahydrofoile acid, aspartic acid, C02, glycine and glutamine Cataboilsm Purine In various tissues there are nucleotidases (which breakdown the nucleotides into nucleosides and phosphoric acids) and nucleosidases (which break down the nucleosides into purine or pyrimidine base and pentose). The released purine bases (adenine and guanine) enter blood and are carried to the liver. In the liver, further cataboilsm occurs as follows: Xanthine, thus obtained is further acted upon by the xanthine oxidase and is converted into uric acid which has the following structure. Uric acid is the end product of purme catabohsm in man, ape, reptiles and birds. In other mammalian species including dog, uric acidis converted into allantoin, which is about 250 times more soluble than uric acid. However, in the Dalmatian coach hound, uric acid (and not allantoin) remains the end product. Conversion of uric acid into allantoin occurs by the action of the enzyme uncase. In the fishes, the allantoin is further converted into urea. In the species Crustacea urea is converted into ammonia. In birds and reptiles uric acid is the end product of not only purine, but also of the nitrogenous residue of the ammo acids. Thus birds and reptiles are called uricotelic animals (see also urea cycle, chap. 7.12) Uric acid is excreted via urine. [Thus, instead of urea, they, ie, birds and reptiles, produce uric acid). Pyrimidine base is cataboinzed to various products including C02, B alanine and b amino isobutyric acid Gout Gout is an ancient disease affecting particularly the middle aged males. Classical gout is not very common in India. In some middle European countries as in Germany, gout is very common. Acute gout is characterized by joint pains (particularly that of the great toe) fever and leucocytosis. The attacks lasts for, if untreated, several weeks. In between the attacks, the person may be remarkably free from symptoms. An important feature of chronic gout is development of tophi (single, tophus), which are swellings found in some regions of the body (e.g.ear). The tophus consists of urates. During the attacks the blood uric acid value (normal 1 to 6 mg/100 ml) is greatly raised. The explanations of the symptom are not dear. However, now it is dear that the excess blood uric acid level is due to overproduction of uric acid. The overproduction is due to the fact that nitrogen and carbon atoms are utilized to form uric acid without becoming nucleotides. Treatment consists of using drugs like probenacid which increases renal excretion of uric acid (uricosuric drug), phenyl butazone and allopurinol. Allopurinol inhibits xanthine oxidase so tha xanthine accumulates but uric acid is not formed. Xanthine does not produce symptoms. PROTEIN SYNTHESIS 1. Introduction : (i) the site of synthesis, (ii) the importance of DNA in the synthesis. (iii) terminology : genetic code, gene codon. Mechanism of the synthesis. Regulation of protein synthesis is, then, to put the particular ammoacid in its particular place in the polypeptide chain and to sew them up (enzymatically). The positioning of the ammoacids are done by the RNA molecu les. The importance of DNA in the synthesis The sequence of ammoacids in a polypeptide chain depends upon the sequence of bases in the RNA molecules. The sequence of bases in the RNA molecule in turn, depends upon the sequence of bases in the DNA molecule. Technically, the sequence of bases is called; the 'code'. So the RNA code depends upon the DNA code. Terminology In a single strand of DNA, the bases like A, T, C, G, project as shown in Fig. 7.13.4. As stated already, the RNA de-velops on such a single strand of DNA and forms a complementary strand. Subsequently, as already stated, the complementary strand leaves the DNA and enters the cytoplasm. Obviously, the sequence of the bases which proiect from this RNA molecule