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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Lichens grow in almost every natural habitat imaginable, from deserts to tropical rain forests—even on the back of certain beetles in New Guinea and inside rocks(along with algae) in the otherwise barren dry valleys of Antarctica.
Many species can not tolerate extreme heat, cold or dryness. Very few, however, can survive heavy air pollution, and many live only where the air is very clean. The disappearance of lichens from an area gives warning of a threatened environment.
1. Which of the following would be the best title for the passage?
A. The versatility and complexity of the lowly lichen
B. The hidden characteristics of algae colonies
C. The disappearance of the lichen species
D. The habitats of spectacular fungi
2. The author states that lichens grow “as though designed to be ignored” because they are
A. not totally understood by botanists
B. troublesome to collect for the purposes of study
C. uncomplicated in their internal structure
D. not easily noticed by observers
3. According to the author, most people are unaware that lichen is a.
A. leafy plant
B. class of simple bacteria
C. two-dimensional life form
D. Combination of organisms
4. The “unique” compounds mentioned in the second paragraph are produced.
A. through the cooperative efforts of the lichen’s parts
B. only under laboratory conditions
C. through one of the three possible processes
D. once in the lichen’s life cycle
5. The author implies that lichens might be used to.
A. find water sources
B. destroy unwanted plant life
C. test for air purity
D. provide food in remote areas
