Nitrogen metabolism anabolism

Urea, the end product of nitrogen metabolism, accumulates rapidly in ARF. Most patients with ARF have a primary stressful illness that results in ureagenesis, and thus protein breakdown is markedly accelerated. Protein catabolism in ARF may be stimulated as the result of insulin resistance, metabolic acidosis, circulating proteases and inflammatory mediators, and the effects of uremic toxins. The mechanism may be direct, via modulation of protein synthesis, or indirect, by inhibiting the action of anabolic hormones. ... 

The topic of nitrogen metabolism includes the biosynthesis and breakdown of amino acids, purines, and pyrimidines also, the metabolism of porphyrins is related to that of amino acids. Many of these pathways, particularly the anabolic ones, are long and complex. In discussing pathways in which the amount of material is large and highly detailed, we shall concentrate on the most important points. Specifically, we shall concentrate on overall patterns and on interesting reactions of wide applicability. We shall also be interested in health-related aspects of this material. Other reactions will be found at the BiochemistryNow Interactive website for this text. It can be considered a repository of supplementary material for this chapter, and we shall refer to it a number of times. 

The urea cycle, which has links to the citric acid cycle, plays a central role in nitrogen metabolism. It is involved in both the anabolism and the catabolism of amino acids. 

What is nitrogen metabolism The metabolism of nitrogen encompasses a number of topics, including the anabolism and catabolism of amino acids, porphyrins, and nucleotides. Atmospheric nitrogen is the ultimate source of this element in biomolecules. 

Male Hormones. The androgenic hormones produced in Ihe testes land adrenal gland t have a w idespread effect upon the development of secondary sexual characteristics (musculature, facial hair, larynx, etc. I. as well as upon the sexual organs and responses themselves. They also promote anabolism tu a marked degree by their effect upon nitrogen and calcium metabolism. The structure of testosterone is shown in the Tahle I. 

Fig. 5.15. Anabolic pathways (synthetic) and central catabolic pathways 14. Only the main biosynthetic routes, and their principal connections to catabolic routes, are shown, in simplified version. The relationships between energy (ATP), and redox (NAD4, NADP ) metabolism, nitrogen...

Beyond this specific effect on the genital tract, the androgens also have a general effect on metabolism. They promote protein synthesis and elevate nitrogen retention. This anabolic effect is also found with several steroids that have been derive by modification of the natural hormone. These derivatives la(-k androgenic properties, for example, l-incthyl-A -androstenolone. Analadie steroids are very useful therapeutically. 

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