Digestion, chemistry

Digestion. Chemistry 431 Biochemistry, Richard A. Paselk, Department of Chemistry, Humboldt State University,... 

Enzymes may be described a organic catalysts of biological origin. The majority are obtained from the interior of cells, but some are obtained from natural secretions such as the digestive juices and milk. For a full discussion of the nature of enzymes and the mechanism of their reactions the student should consult a work such as Chemistry and Methods of Enzymes, by J. B. Sumner and G. F. Somers (Academic Press, New York), or Enzymes, by M. Dixon and E. C. Webb[(Longman Group Ltd.). The following points should however be noted ... 

Ana.eroblc Digestion. Methane can be produced from water slurries of biomass by anaerobic digestion in the presence of mixed populations of anaerobes. This process has been used for many years to stabilize municipal sewage sludges for purposes of disposal. Presuming the biomass is all cellulose, the chemistry can be represented in simplified form as follows ... 

Figure 9.6 Surfer-generated chromatoeletropherogram of fluorescamine-labeled tryptic digest of ovalbumin. Reprinted from Analytical Chemistry, 62, M. M. Bushey and J. W. Jorgenson, Automated instrumentation for comprehensive two-dimensional high-performance liquid chromatography/capillary zone electrophoresis, pp 978-984, copyright 1990, with permission from the American Chemical Society.

Ester hydrolysis is common in biological chemistry, particularly in the digestion of dietary fats and oils. We ll save a complete discussion of the mechanistic details of fat hydrolysis until Section 29.2 but will note for now that the reaction is catalyzed by various lipase enzymes and involves two sequential nucleophilic acyl substitution reactions. The first is a trcinsesterificatiori reaction in which an alcohol gioup on the lipase adds to an ester linkage in the tat molecule to give a tetrahedral intermediate that expels alcohol and forms an acyl... 

Amide hydrolysis is common in biological chemistry. Just as the hydrolysis of esters is the initial step in the digestion of dietary fats, the hydrolysis of amides is the initial step in the digestion of dietary proteins. The reaction is catalyzed by protease enzymes and occurs by a mechanism almost identical to that we just saw for fat hydrolysis. That is, an initial nucleophilic acyl substitution of an alcohol group in the enzyme on an amide linkage in the protein gives an acyl enzyme intermediate that then undergoes hydrolysis. 

The fact that tantalum and niobium complexes form in fluoride solutions not only supplements fundamental data on the coordination chemistry of fluoride compounds, but also has a broad practical importance. This type of solution is widely used in the technology of tantalum and niobium compounds in raw material digestion, liquid-liquid extraction, precipitation and re-pulping of hydroxides, and in the crystallization and re-crystallization of K-salts and other complex fluoride compounds. 

Kenneth A. Jacobson Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA... 

The growth of a child, the production of polymers from petroleum, and the digestion of food are all the outcome of chemical reactions, processes by which one or more substances are converted into other substances. This type of process is a chemical change. The starting materials are called the reactants and the substances formed are called the products. The chemicals available in a laboratory are called reagents. In this section, we see how to use the symbolic language of chemistry to describe chemical reactions. 

Fig. 36 Tapping mode AFM images of L4K8L4-VPRGS-PEG (a) before and (b) after thrombin digestion (at pH 9). Fibres in (b) have diameters of about 5-6 nm. Adapted by permission of The Royal Society of Chemistry from Koga et al. [79]...

As described in Section 4-1. one important class of chemical reactions involves transfers of protons between chemical species. An equally important class of chemical reactions involves transfers of electrons between chemical species. These are oxidation-reduction reactions. Commonplace examples of oxidation-reduction reactions include the msting of iron, the digestion of food, and the burning of gasoline. Paper manufacture, the subject of our Box, employs oxidation-reduction chemishy to bleach wood pulp. All metals used in the chemical industry and manufacturing are extracted and purified through oxidation-reduction chemistry, and many biochemical pathways involve the transfer of electrons from one substance to another. 

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

The alkali process uses sodium hydroxide and is well known as Bayer s process. It involves relatively simple inorganic and physical chemistry and the entire flowsheet can be divided into caustic digestion, clarification, precipitation and calcination. Although mineral assemblage in bauxites is extensive, processing conditions are primarily influenced by the relative proportions of alumina minerals (gibbsite and boehmite), the iron minerals (goethite and hematite), and the silica minerals (quartz and clays-usually as kaolinite). 

Schwarcz, Joe. Radar, Hula Hoops, and Playful Pigs 67 Digestible Commentaries on the Fascinating Chemistry of Everyday Life. New York Henry Holt Co., 2002. 

Two processes are used in the manufacture of titanium dioxide pigments the sulfate process and the chloride process. The chemistry of the sulfate process, the longer established of the two methods, is illustrated schematically in Scheme 9.1. In this process, crude ilmenite ore, which contains titanium dioxide together with substantial quantities of oxides of iron, is digested with concentrated sulfuric acid, giving a solution containing the sulfates of Ti(iv), Fe(m) and Fe(n). Treatment of this... 

Detective story set in 1699, with an alchemical thread. The 17 chapters are headed with alchemical processes - Conjunction, Imbibation, Revivification, Resolution, Decoction, Disintegration, Digestion, Mortification, Lixiviation, Division, Elevation, Foliation, Fulmination, Ablation, Coagulation, Incineration, Projection. A note thanks Denns William Hauck for his help with the chemistry of alchymy... 

Orellana G., Moreno-Bondi M.C., From Molecular Engineering of Luminescent Indicators to Environmental Analytical Chemistry in the Field with Fiber-Optic (Bio)sensors, in 15th Optical Fiber Sensors Conference Technical Digest (OFS-2002), IEEE, Piscataway, NJ, 2002 pp. 115-118 (ISBN 0-7803-7289-1). 

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