Living Organisms and Cells

Each cell consists primarily of a membrane, which separates it from the environment, preserves its structural integrity, and keeps it apart from other cells or from the surrounding environment. Plant cells, unlike animal cells, also have, in addition to a cell membrane, a cell wall, composed of cellulose and lignin. The cell wall provides structural strength not only to the vegetable cell itself but to all plant tissues as well. Inside the membrane, the interior of the cell, known as the protoplasm, includes two main 

The nucieus contains bundies of a fibrous materiai known as chromatin, which is made up of mixed proteins and deoxyribonucieic acid (DNA), the substance that carries the genetic information of the iiving organism of which the ceii is a component. Aii ceiis repiicate by division. When a ceii repiicates, DNA in the chromatin of the nucieus passes the genetic information from one generation to the next one. As the cell divides, the chromatin ciusters into rodiike structures known as chromo- 

TABLE 62 Number of Chromosomes in the Cells of Living Orgcmisms 

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Proteias are metabolized coatiauously by all living organisms, and are ia dyaamic equilibrium ia living cells (6,12). The role of amino acids ia proteia biosyathesis has beea described (2). Most of the amino acids absorbed through the digestioa of proteias are used to replace body proteias. The remaining portioa is metabolized iato various bioactive substances such as hormones and purine and pyrimidine nucleotides, (the precursors of DNA and RNA) or is consumed as an energy source (6,13). 

The reactant is referred to as a substrate. Alternatively it may be a nutrient for the growth of cells or its main function may require being transformed into some desirable chemical. The cells select reactants that will be combined and molecules that may be decomposed by using enzymes. These are produced only by living organisms, and commercial enzymes are produced by bacteria. Enzymes operate under mild conditions of temperature and pH. A database of the various types of enzymes and functions can be assessed from the following web site http //www.expasy.ch/enzyme/. This site also provides information about enzymatic reactions. 

Cells are the basic units for all living organisms. All cells are bounded by a membrane, and bacterial and plant cells have a cell wall. The membrane protects the cell from the outside environment. It consists of a lipid bilayer (Fig. A2.1). The function of the membrane is to control materials that enter and exit the cell and enable biochemical reactions to take place within the cell. 

Like living organisms themselves, cells come in a remarkable variety of flavors. Brown has described what might be a human cell with elaborate internal structure. However, there is no such a thing as a typical cell. Afunctional liver cell, a hepatocyte, is quite distinct from a nerve cell, a neuron, that, in turn, is not much like a cell of the retina of the eye. Skin cells, pancreatic cells, kidney cells, cells of the testis and ovary, red blood cells, bone cells, and on and on, are all structurally, functionally, and metabolically distinct. Indeed, there are several types of cells in the skin, pancreas, kidney, testis, ovary, and bone. Then there are the cells of bacteria and other microorganisms that have no nucleus or other membrane-limited organelles very different. Diversity abounds. 

DNA (deoxyribonucleic acid) is well known as the molecule that bears all of the genetic information necessary to construct and operate a living organism. The cell nuclei of all eucaryotic organisms contain DNA and each cell contains all the genetic code needed to assemble the entire organism - a remarkable duplication of information. The amount of information involved requires the individual DNA... 

In living organisms, each cell produces thousands of proteins and one set of these proteins is called a proteome. Their analysis is a tedious job. Moreover, the low amounts of proteins in a proteome makes this task challenging. Fortunately, the development of microfluidic devices including NCE is the best innovation of the last decade to solve such types of riddles. Many papers have been published on proteomics analysis using NCE some... 

Microbial polysaccharides constitute a specific class of biopolymers. These biopolymers are formed during the growth of the living organisms, and are thus, called natural polymers. Their synthesis usually involves enzymatic catalysis and an increase in the chain through polymerization reactions of the monomers, typically inside the cells, mediated by complete metabolic processes (3,4). 

Necrosis The process of cell death within a living organism and the end result of irreversible changes following cellular injury. 

Genetic information is stored in DNA molecules. The sequence of bases in a particular piece of DNA specifies the sequence of amino acids in a particular protein. Exactly how the DNA is replicated when a cell divides and how the information in the DNA sequence is converted to an amino acid sequence of a protein are of critical importance to the functioning of a living organism and comprise a major part of any modern biochemistry textbook. We have space here only to briefly outline these processes. 

Sulfur compounds are widespread in Nature in living organisms and this is also reflected in the geochemistry of sulfur. A constituent of amino acids (cysteine, methionine) and of cofactors such as biotin, thiamine, and coenzyme A, sulfur is essential for the maintenance of cells. Inorganic sulfur compounds, in the Earth s crust, the sea, and the atmosphere are converted by plants and microorganisms into organosulfur compounds, while the demands of animals and humans for sulfur is much lower and is usually met by the oxidation of amino acids. 

The antigen then is mixed with serial dilutions of the enzyme-labeled antibody. A chromogenic substrate mixed with the conjugated enzyme yields a water-soluble product, the absorbency of which can be measured by a spectrophotometer. Recent technology has led to the development of rapid tests that do not require intact cells, live organisms, or cell cultures. ELISAs using monoclonal antibody techniques for the rapid detection of HSVs, adenoviruses, and C. trachomatis are highly sensitive and specific. 

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