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 suprprising 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
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”
选择答案：查看解析
