【正文】 of engineering principles to microscopic biological systems that are used to create new products by synthesis, including the production of protein from suitable raw materials.Humanfactors engineering This concerns the application of engineering, physiology, and psychology to the optimization of the humanmachine relationship.Environment health engineering Also called bioenvironmental engineering, this field concerns the application of engineering principles to the control of the environment for the health, fort, and safety of human beings. It includes the field of lifesupport systems for the exploration of outer space and the ocean.LESSON 22 Genetic EngineeringThis slightly misleading term covers the recent development of techniques concerned with producing what are effectively controlled mutations—deliberate evolution. The techniques, often colorfully called “gene splicing”, are methods of constructively rearranging the genetic code to produce an organism with new, desirable characteristics. In the case of a simple microbe, this might involve introducing the ability to produce a certain chemical. Somewhere on the DNA molecule is the information (gene) concerned with this desired quality or product. The “engineering” is concerned with “cutting out” that part of the string, and joining or grafting this into another organism.This is not, of course, done with a knife, but chemically by using special enzymes. The discovery of this way to “restriction enzymes”, by Stanley Cohen and Herbert Boyer in the early 1970s, supplied a tool that would cut the long DNA molecule into a fixed number of defined fragments. The enzyme does this by recognizing and attacking certain specific nucleotide sequences in the DNA chain. There are now well over 300 of these enzymes in general use, each “tuned” to a different sequence. “Splicing” is done with another set of enzymes called “l(fā)itigation” enzymes, which can stick the fragments back together.All this talk of “cutting” and “splicing” perhaps suggests delicate surgery, but it must be remember that all these functions are in practice carried out chemically in solution. The molecular biologist/genetic engineer often ends up with a “soup” posed of fragments of the genetic code. Somewhere in there is the coding for the desired characteristic, but unneeded sequences will also be present. There are a number of techniques that have been developed to help in the selection of those fragments he wishes to process.If a DNA sample is placed on a plate of gel under appropriate chemical conditions and a weak electric current is passed across the plate, the fragments will to “migrate” in the direction of the positive pole. The smaller ones move faster, and after several hours they are all arranged in a neat line from the shortest to the longest.Electrophoretic separation can be used to determine the sequence of “bases” in a DNA fragment or to separate specific molecules from one another. The DNA synthesizer (or “gene machine”) is a fairly recent development that promises greatly to expand the scope of the genesplicer. Since there are only four ponents (however plicated their permutations and binations) to the DNA string, it has been possible to construct an apparatus that can create a specific sequence of DNA, a synthetic gene.When a desired fragment is identified or synthesized it can be reinserted into a “host” organism. Genetic engineers tend to chose microorganisms with thoroughly known characteristics. The resulting “engineered” organism is then “cloned” from a single cell grown and multiplied in the usual way and if the process is successful it will breed truea new organism with an added ability engineered in. To get DNA into a “host” a “vector” must be used. Usually this is a small piece of DNA which is attached to the new DNA and when inserted “rebines” again with the chromosomal DNA using natural processes usually involved in the cell’s reproduction.The process has two distinct aims. It can simply be used to increase the production capability of the microbe concerned. This, known as “amplification”, consists of increasing the number of gene sequences devoted to the production of the desired substance. Alternatively, an entirely new production ability can be grafted in. Genetic material from literally any source, plant or animal, can be inserted into a microbe whose growth and fermentation characteristics are thoroughly well known.LESSON 23 How We Digest CarbohydratesWhile any of the monosaccharides, glucose or fructose for example, easily penetrates the intestinal wall to enter the bloodstream, neither disaccharides nor the larger carbohydrates normally get through the intestinal barrier. They are too large. To assimilate these larger carbohydrates, from maltose and sucrose to starch, we must first clip them down to their ponent monosaccharides, which are able to pass through the intestinal wall and into the bloodstream. (4) As we’ve seen, in forming the larger carbohydrate molecules the individual monosaccharide rings connect to each other with loss of a molecule of water. (4) To reverse this process, to cleave the disaccharides and the polysaccharides to their ponent monosaccharides, we must return the water to the molecules through hydrolysis.Our bodies carry out this hydrolysis through the catalytic action of our digestive enzymes. Enzymes, you’ll recall, act as biological catalysts that allow chemical reactions to take place more rapidly or under milder conditions than they might otherwise, but are not consumed themselves. In cleaving the nutrient polysaccharides quickly and efficiently in the relatively mild chemical environment of our digestive systems, these molecular catalysts act very much like the platinum and palladium catalysts that help remove unburned hydrocarbons from automobile exhausts.An enzyme that enables us to digest both maltose and starch is maltase, which our bodies produce in sufficient quanti