Nucleic acids in cells include two molecules, DNA and RNA, which are combined with proteins to form nucleoprotein. DNA and protein combine to form deoxyribonucleoprotein (DNP), and RNA and protein combine to form ribonucleoprotein (RNP). The DNA of eukaryotes is divided into chromosomal DNA and organelle DNA. The former is located in the nucleus, about 95%, is a double-stranded linear molecule; the latter is present in mitochondria or chloroplast and other organelles, about 5%, is a double-stranded circular molecule. In addition, there are double-stranded circular plasmid DNA in prokaryotes; in non-cellular virus particles, the existence of DNA in various forms, including double-stranded circular, single-stranded circular, double-stranded line The shape is divided into single-stranded linear. The total length of DNA molecules varies greatly between different organisms and generally increases with the evolution of the organism. For example, human DNA is composed of about 3.0 × 109 base pairs (bp), which is about 5.7 × 105 times longer than the simian virus 40 (SV40) of 5? 243bp. Relatively speaking, RNA molecules are much smaller than DNA molecules. Because the functions of RNA are diverse, the types, sizes, and structures of RNA are more diverse than DNA. The difference in the nature of DNA and RNA determines that the optimal separation and purification conditions for the two are different. Selection of materials and methods (1) Selection of materials and methods Common clinical specimens include blood, urine, saliva, tissues, and cultured cells. There are many methods for nucleic acid separation and purification. How to properly collect and prepare materials and choose a suitable separation and purification method is a primary issue. First of all, we should make sure that the separation and purification of nucleic acids is not the ultimate goal. Different experimental research and applications may have different requirements on the yield, integrity, purity and concentration of nucleic acids; as for the time and cost required for the isolation and purification of nucleic acids Often need to be considered; without affecting the quality of nucleic acids, safe and non-toxic reagents and programs should be selected. In recent years, the development of kits and the use of automated instruments have enabled batch preparation of nucleic acid samples, greatly improving the efficiency of separation and purification. (2) The principle of choice There are many methods for nucleic acid isolation and purification, and different solutions should be taken according to the nature and initial amount of the specific biological material and the nature and use of the nucleic acid to be isolated. Regardless of the method, the general principles should be followed: First, the integrity of the primary structure of the nucleic acid is guaranteed, because a complete primary structure is the most basic requirement for the study of nucleic acid structure and function; second, the contamination of other molecules is excluded as much as possible To ensure the purity of nucleic acid samples, this is the main content discussed in this chapter. (3) Maintenance of nucleic acid integrity In order to ensure the integrity of the nucleic acid, during the operation, first of all, try to avoid the destruction of the nucleic acid by various harmful factors. There are many factors that affect the integrity of nucleic acids, including physical, chemical and biological factors, some of which can be avoided. If it is too acid or too alkaline, it can damage the phosphodiester bond in the nucleic acid chain. During the extraction of nucleic acid, use a suitable buffer and always control the pH between 4 to 10, which can be avoided. Harmful; in addition to high temperature heating, in addition to the high temperature itself destroying the chemical bonds in the nucleic acid molecules, it may also bring liquid shear force due to boiling, so nucleic acid extraction is often carried out under the condition of 0 ~ 4 ℃.
Belt conveyor, also known as belt conveyor, is a kind of continuous transportation machinery, but also a kind of general machinery. Belt conveyor is widely used in ports, power plants, iron and steel enterprises, cement, grain and light industry production lines. That is to say, bulk materials can be transported, or items can be transported. The noise is small and the structure is simple. Belt conveyor can be used for horizontal or inclined transportation. The belt conveyor is also applied to continuous transportation mobile machines such as loaders, unloaders, stackers and reclaimers. The belt conveyor is composed of belt, frame, driving roller, steering roller, bearing spoke, return roller, tensioning device, cleaner and other parts. In large ports or metallurgical enterprises, belt conveyor is widely used. Its total length can reach more than ten kilometers.
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