Catabolism nucleic acids

Normal blood pH is 7.35-7.45 (corresponding to 35-45 nmol of H+ per liter). Values below 6.80 (160 nmol of H+ per liter) or above 7.70 (20 nmol of H+per liter) are seldom compatible with life. A large amount of acid produced is a byproduct of metabolism. The lungs remove 14,000 mEq of CO2 per day. From a diet that supplies 1 -2 g of protein per kilogram per day, the kidneys remove 40-70 mEq of acid per day as sulfate (from oxidation of sulfur-containing amino acids), phosphate (from phospholipid, phosphoprotein, and nucleic acid catabolism), and organic acids (e.g., lactic, )3-hydroxybutyric, and ace-toacetic). These organic acids are produced by incomplete oxidation of carbohydrate and fats, and in some conditions (e.g., ketosis see Chapter 18) considerable amounts may be produced. 

Caffeine (1,3,7-triniethylxanthine) is the well-known stimnlant present in tea and coffee. Uric acid, the end product of nucleic acid catabolism in humans, birds and reptiles (nric acid was one of the first heterocyclic compounds to be isolated as a pure substance, by the Swedish chemist Carl Scheele in 1776) is formed by the action of the enzyme xanthine oxidase. In cases of excess uric acid, deposition of crystals of uric acid can occur, leading to the joint pain known as gout, usually initially in the big toe and usually in males. 

Ammonia is generated mainly from the metabolism of amino acids and from the catabolism of purine and pyrimidine bases, which are produced from nucleic acids. Since it is toxic, it must be converted to a non-toxic compound for excretion from the body. This is achieved via the ornithine cycle, more usually known as the urea cycle. 

Proteins and nucleic acid Increase urinary nitrogen during fasting Anti-anabolic (catabolic) effect... 

Uric acid is the excreted end product of purine catabolism in primates, birds, and some other animals. A healthy adult human excretes uric acid at a rate of about 0.6 g/24 h the excreted product arises in part from ingested purines and in part from turnover of the purine nucleotides of nucleic acids. In most mammals and many other vertebrates, uric acid is further degraded to al-lantoin by the action of urate oxidase. In other organisms the pathway is further extended, as shown in Figure 22-45. 

J to their molecular components. Then one of two things happens either your body burns these molecular components for their energy content through a process known as cellular respiration, or these components are used as the building blocks for your body s own versions of carbohydrates, lipids, proteins, and nucleic acids. The sum total of all these biochemical activities is what we call metabolism. Two forms of metabolism are catabolism and anabolism, and Figure 13.41 shows the major catabolic and anabolic pathways of living organisms. 

The types of biomolecules produced by anabolism are the same as the types found in food—carbohydrates, lipids, proteins, and nucleic acids. These products of anabolism are, if you will, the hosts own version of what the food once was. And if the host ever becomes food, anabolic reactions in the subsequent host will result in different versions of the molecules. Thus, organisms in a food chain live off one another by absorbing one another s energy via catabolic reactions and then rearranging the remaining atoms and molecules via anabolic reactions into the biomolecules they need to survive. 

Purine bases from ingested foods, or formed by catabolism of nucleic acids, are able to react with PRPP under the influence of phosphoribosyltransferases.3063 Two such enzymes are known to act on purines. One converts adenine to AMP (Fig. 25-17, step b) and also acts upon 5-aminoimidazole-4-carboxamide. This enzyme may be especially important to parasitic protozoa such as Leishmania, which lack the de novo pathway of purine synthesis (Fig. 25-15).278/306b... 

As indicated in Fig. 25-18, free adenine released from catabolism of nucleic acids can be deaminated hydrolytically to hypoxanthine, and guanine can be deaminated to xanthine.328 The molybdenum-containing xanthine oxidase (Chapter 16) oxidizes hypoxanthine to xanthine and the latter on to uric acid. Some Clostridia convert purine or hypoxanthine to xanthine by the action of a selenium-containing purine hydroxylase.3283 Another reaction of xanthine occurring in some plants is conversion to the trimethylated derivative caffeine. 328b One of the physiological effects of caffeine in animals is inhibition of pyrimidine synthesis.329 However, the effect most sought by coffee drinkers may be an increase in blood pressure caused by occupancy of adenosine receptors by caffeine.330... 

Biological Reactions. Biosynthesis and catabolism of biological molecules (amino acids, carbohydrates, lipids, nucleic acids, peptides/proteins), metabolic cycles, biological catalysis and kinetics, mechanisms, organic and inorganic cofactors. 

Nucleotidases have been studied in liver from various species and activity has been identified in lysosomes, cytoplasmic supernatants and plasma membrane preparations. Arsenis and Touster (31) have purified a 5 -nucleotidase from rat liver lysosomes to apparent homogeneity. The enzyme is unusual in that it hydrolyzes 2 -, 3 -, and 5 -mononucleotides equally well with preference for 5 -dAMP. It also hydrolyzes FMN, p-nitrophenyl phosphate, and /J-glycerol phosphate, but not inorganic pyrophosphate or bis(p-nitrophenyl) phosphate. Unlike the 5 -nucleotidases described thus far, divalent cations such as Co2+, Mn2+, and Mg2+ have no activating effect, but EDTA is inhibitory. In spite of the broad substrate specificity kinetic experiments indicate that a single enzyme is involved. Because of its broad substrate specificity it has been suggested (SI) that it may play a key role in lysosomal catabolism of nucleic acids. 

Biochemically, folacin functions in vivo as coenzymes and carriers of one-carbon units for a number of enzyme reactions, including synthesis of amino acids, proteins, and nucleic acids (58,120,122). Folacin participates in both anabolic and catabolic reactions, and its metabolism is cyclic in nature. Greater detail on the biochemistry of folacin is available (120,122). 

A schematic block diagram of the metabolism of a typical aerobic heterotroph. The block labeled Catabolism represents pathways by which nutrients are converted to small-molecule starting materials for biosynthetic processes. Catabolism also supplies the energy (ATP) and reducing power (NADPH) needed for activities that occur in the second block these compounds shuttle between the two boxes. The block labeled Biosynthesis represents the synthesis of low- to medium-molecular-weight components of the cell as well as the synthesis of proteins, nucleic acids, lipids, and carbohydrates and the assembly of membranes, organelles, and the other structures of the cell. 

Adenine phosphoribosyltransferase catalyzes the conversion of adenine to AMP in many tissues, by a reaction similar to that of hypoxanthine-guanine phosphoribosyltransferase, but is quite distinct from the latter. It plays a minor role in purine salvage since adenine is not a significant product of purine nucleotide catabolism (see below). The function of this enzyme seems to be to scavenge small amounts of adenine that are produced during intestinal digestion of nucleic acids or in the metabolism of 5 -deoxy-5 -methylthioadenosine, a product of polyamine synthesis. 

Although purine nucleosides are intermediates in the catabolism of nucleotides and nucleic acids in higher animals and humans, these nucleosides do not accumulate and are normally present in blood and tissues only in trace amounts. Nevertheless, cells of many vertebrate tissues contain kinases capable of converting purine nucleosides to nucleotides. Typical of these is adenosine kinase, which catalyzes the reaction... 

Molybdenum Cofactor for enzymes involved in catabolism of certain amino acids and nucleic acids Men women 45 pg/d... 

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