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  • ID:9406-6635

    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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  • ID:9406-6836
    Wide-ranging research on tooth decay has recently produced some surprising findings. One indicates that cheddar may actually inhibit the tooth-decay process. It seems to have decay-slowing effect on human teeth if it is eaten immediately after sugar. Why cheese should have such an effect is unknown. It is speculated that the food might interfere with the acid that decays teeth or with bacteria that produce the acid. If so, it would be the first common food found to have this useful property. The other surprising research finding was that heavily sweetened cereals proved about equally potent in causing decay whether they contained eight percent sugar or almost eight times that much.
    1. According to the passage, how many of the test results were unexpected?
    A. One B. Two C. Three D. Eight
    2. According to the passage, what effect does cheddar cheese seem to have?
    A. It interferes with the function of teeth.
    B. It makes sugar taste sweeter.
    C. It decreases the rate at which teeth decay.
    D. It helps in the digestion of food.
    3. It can be inferred from the passage that the research on the relationship between cheese and tooth.
    A. has been discredited B. will be slowed considerably
    C. has been found to be conclusive D. will be continued
    4. Researchers discovered that sweetened cereals were.
    A. important nutritionally
    B. all surprisingly heavy in sugar
    C. more expensive than cheese
    D. all equally harmful to teeth

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  • ID:9406-6628

    (翻译)The establishment of L-glutamic acid fermentation provided a significant impetus to the development of microbial production of primary metabolites. Encouraged by the establishment of the L-glutamic acid fermentation, various research projects have been carried out in the attempt to isolate wild strains or derive genetic mutants producing various kinds of amino acids. As a result, almost all of the amino acids are now commercially produced by fermentation.

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  • ID:9406-6828
    Not all organisms exhibit semiconservative replication.( )

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  • ID:9406-6803
    Fungal mitosis, unlike mitosis in all other organism, occurs within the nucleus.( )

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  • ID:9406-6808



    Lichens can be spectacular for anyone who cares to look ,but few people take the trouble. Often modestly colored and seemingly two-dimensional as they cling to whatever surface they find, they grow in the background; as though designed to be ignored. Yet they hold a special fascination for botanists, partly because they present mysteries still to be solved and partly because they do so many things so well.

    No casual observer of a lichen would ever suspect that it was a composite of interacting life forms. The seemingly uncomplicated lichen is actually composed of a fungus and a colony of algae (or blue-green algae, which some scientists now consider to be bacteria). A few species even include all three of these diverse forms of life. A complete lichen is strikingly different from its separated partners in both appearance and biochemistry; many produce unique compounds which cannot be made by the component organisms alone.

    Lichens grow in almost every natural habitat imaginable, from deserts to tropical rain forestseven 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 lichens parts

    B. only under laboratory conditions

    C. through one of the three possible processes

    D. once in the lichens 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

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