（翻译）载体是一个复制子，其基因可保留在寄主细胞内，载体包括质粒和寄主于细菌的噬菌体。质粒载体应含有一些单一的普通限制性内切酶的切点，还要有一段抗生素抗性的决定子，以便于选择转化子。切断载体所用的酶与切断染色体DNA的内切酶相同，得到的DNA片段与线状的载体在有DNA连接酶存在的情况下混合培养，产生共价连接的DNA分子，结果，混合物中可得到多种多样的DNA分子。这包括二聚体、三聚体和多聚体DNA片段以及重新环化的质粒。其中有些质粒会插入一段目标DNA片段，这样就得到了杂合的质粒，即重组质粒。
Notes:
噬菌体 phage 限制性内切酶 restriction endonuclease
抗生素抗性 antibiotic resistance 决定子 determinant
共价的 covalently 二聚体 dimers
三聚体 trimers 多聚体 multimers
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Immobilization of enzymes
Enzymes are often used as nonrecoverable chemical reagents, in which case they are added to the substrate incubated at the required temperature and pH for a period and subsequently destroyed. Amylase, proteases and other inexpensive bulk enzymes are used in this way. Alternatively, enzymes may be attached to an inert support (immobilized). This offers the advantages of (1) recovery and re-use of the enzymes, in batch reactors; or (2) the development of continuously operated enzyme reactions similar to continuous fermentation systems used for microorganisms; (3) the possibility of multi-enzyme systems; and (4) the enzyme does not remain in the processed solution. However, there are some disadvantages, the enzyme may be stabilized by immobilization but it may also lose activity, and the process becomes technically more complex.
There are many ways to immobilize enzymes, the common procedures involve (1)absorption to an insoluble support of either organic or inorganic origin. Cellulose, dextran, nylon and bentonite are some of the many carriers that have been used. Attachment may be by physical adsorption, ionic binding or covalent bonding. (2) Entrapment methods in which the enzyme is localized within a polymer matrix are popular and include gel or fiber entrapment and microencapsulation in which the enzyme is enclosed within sperical semipermeable polymer membranes. (3) A simple but effective procedure is to immobilize the enzyme within the host cell by heat treatment or covalent cross-linking following by pelleting the cells.
Are the following statements true or false?
（1）Amylase, proteases and other inexpensive bulk enzymes are destroyed after the enzyme-catalyzed reaction is completed
（2）The advantages of immobilization of the enzymes include the stability of the enzymes and the increase of the enzyme activity
（3）By immobilization of the enzymes, it is possible to operate the enzyme reactions continuously
（4）In the last paragraph, the word “insoluble support” has the same meaning as the word “carrier”
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