Cellular structure, enzyme

The mechanism whereby the bacteria produce the disease with its attendant symptoms is often due to the cells ability to produce specific poisons, toxins or aggressins (Chapter 14). Many of these are tissue-destroying enzymes which can damage the cellular structure ofthe body or destroy red blood cells. Others (neurotoxins) are highly specific poisons ofthe central nervous system, for example the toxin produced by Clostridium botulinum is, weight for weight, one ofthe most poisonous substances known. 

A common characteristic of metabolic pathways is that the product of one enzyme in sequence is the substrate for the next enzyme and so forth. In vivo, biocatalysis takes place in compartmentalized cellular structure as highly organized particle and membrane systems. This allows control of enzyme-catalyzed reactions. Several multienzyme systems have been studied by many researchers. They consist essentially of membrane- [104] and matrix- [105,106] bound enzymes or coupled enzymes in low water media [107]. 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

Taking into account that heat treatment inactivates some oxidative enzymes and causes the rupture of some cellular structures, greater extractability of carotenoids is expected to occur in processed foods. Therefore, when mild temperatures are applied, it is very common to obtain higher carotenoid content in a processed food as compared to its fresh counter part. For example, total... 

Lemaire-Gony, S. and P. Lemaire. 1992. Interactive effects of cadmium and benzo[a]pyrene on cellular structure and biotransformation enzymes of the liver of the European eel Anguilla anguilla. Aquat. Toxicol. 22 145-160. 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

Some fruit types (e.g. pome fruits such as apples and peal s) require mechanical treatment (milling) coupled with a biochemical process (involving enzymes) to break down the cellular structure and obtain best yields. It is possible to achieve almost total hquefaction by means of an appropriate enzyme cocktail. 

Note that even human tissues fixed immediately after their removal from the body may undergo cellular changes because usually the vascular supply is terminated before the tissue is surgically removed. During this duration ( 1 hr) the tissue remains at body temperature, at which the activity of digestive enzymes continues, damaging the cellular structures (Grizzle et al., 2001). 

Digestion Techniques For nonvascularized or low-water-content tissues such as bone, cartilage, or hair, a mechanical technique may do little to disrupt cellular structure and extract analytes. Extreme measures such as digestion with strong acid (i.e., 12 N HC1) are routinely used for DNA or nucleic acids, which can tolerate the harsh conditions. Alternatively, certain enzymes can be used to digest tissue samples. Commercial devices are available which contain digestion bombs fabricated from material resistant to corrosive media. 

During transcription of information from DNA into mRNA, the two complimentary strands of the DNA partly uncoil. The sense strand separates from the antisense strand. The antisense strand of DNA is used as a template for transcribing enzymes that assemble mRNA (transcription), which, in the process produces a copy of the sense strand. Then, mRNA migrates into the cell, where other cellular structures called ribosomes read the encoded information, its mRNA s base sequence, and in so doing, string together amino acids to form a specific protein. This process is called translation. ... 

Of course, in addition to the requirement for an unbiased extraction methodology, it is imperative that all enzymic activity is quenched throughout the extraction and sample preparation. Typically, this is assumed to be the case when extracting in organic solvents, although numerous enzymes may retain activity in such environments. The physical nature of the samples themselves has an impact upon the efficiency of extraction of metabolites. For example, eukaryotic and prokaryotic samples behave very differently during the several steps of classic sample preparation methods. Even within the eukaryotes alone, there is a vast diversity of cellular structures that would seem to make it imprudent to blindly adopt protocols that were devised for other organisms or tissues. 

The body contains many amino acids, some of which can be synthesized (non-essential amino acids), while others must be absorbed from the diet (the essential amino acids). Amino acids are the building blocks of protein, being attached together in groups to form the proteins that the body needs as part of its cellular structure or as enzymes, which are biological catalysts. Glutamate can be synthesized in the body, and it is also absorbed from food, in which it occurs as the free amino acid, or it can be released from proteins by digestion. 

Probes of Cellular Structure. The membrane matrix of animal cells contains, among other compounds, enzymes, proteins, phospholipids, and triglycerides. The rate and extent of release of these compounds from the membrane during selective enzymatic digestion can be used to probe the degree of exposure of these compounds to the surface environment. 

Histochemical techniques for detecting substrate before and after enzyme treatment are extremely useful in studies on cellular structure. One of the oldest histochemical tests utilized saliva to identify suspected glycogen or starch. More definitive results are obtained when thin sections of a tissue are incubated in a buffered solution of purified amylase and stained for poly-utc-glycols. Material stained by periodic acid-Schiff reagent in the control, but not in the section exposed to amylase, is assumed to be glycogen or starch. Two more of the numerous histochemical techniques associated with localization of substrate are—using hya-luronidase to locate hyaluronic acid and chondroitin 4- and 6-sulfates (179) and using neuraminidases to locate sialomucins (180). By use of electron microscopy in combination with the histochemical technique subcellular localization can be obtained. 

Cytochemical determination of the subcellular localization of enzymes has been very successful in studies on cellular structure (183)... 

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