نمونه سوالات آزمون های کارشناسی ارشد بیوتکنولوژی و داروسازی زبان عمومی و تخصصی امتحانات 94-86 - بخش (3)

When producing chemicals is concerned, living organisms, such as microbes and plants, have a number of important advantages over conventional chemical refineries. Not only can they often produce more complex chemical compounds, but they also use renewable feed stocks, such as sugars, carbon dipxide and sunlight rather than petroleum. However, they have one major disadvantage: a chronic lack of flexibility. Whereas chemical refineries can be designed to produce a huge array of diverse chemical compounds, with natural organisms you get what you are given. Our ability to engineer biology has always far lagged behind our ability to engineer chemistry. But that is beginning to change. What started with the transfer of single genes between organisms has now progressed to the ability to insert and modify entire metabolic pathways and genetic control systems. This is resulting in the development of natural organisms able to produce complex chemicals that are entirely alien to them, and the rise of a totally new field known as synthetic biology.

Bioremediation involves using natural bacteria and enzymes to digest chemicals into harmless carbon dioxide, water and microbial material. It is surprising what a wide range of chemicals bacteria and other micro-organisms can thrive on including oil, benzene, pesticides and polycyclic aromatic hydrocarbons. So why don`t contaminated soils just clean themselves up? There are two main reasons: either a lack of bacteria which are able to degrade the polluting chemicals, or the bacteria present are not degrading effectively. It used to be thought that many soils did not contain bacteria which were capable of attacking complex organic chemicals, so specially-cultured bacteria were added to promote their remediation. However with the majority of contaminants this was unnecessary, and usually failed. In general, most soil contaminants can be digested by the bacteria already present in the soil (the indigenous bacteria), if only they can be given the right conditions. If there are few indigenous bacteria in the soil then a natural mixed bacterial culture such as organic matter or normal soil can be added.