单选题
Imagine a bacterium that, when injected into the
bloodstream, would travel to the site of a tumor, insert itself into the cancer
cell, and then produce a cancer-killing compound. That's exactly what scientists
at the University of California, Berkeley(UCB) and University of California, San
Francisco(UCSF) have set out to do. Traditional cancer
therapies are limited for two key reasons: little of the drag actually reaches
the tumor and the drug is toxic to both cancerous and healthy tissues. Bacteria,
however, have the potential to precisely target cells. "In a way, bacteria are
the ultimate in smart drugs," says George Church, a geneticist at Harvard
Medical School in Boston (he was not involved in the current work, but will
collaborate on the project in the future). "It's hard to pack a lot of
intelligence into a small molecule or protein; but bacteria can have sensors and
actuators and can drill into a cell, like a submarine." To
build a cancer-killing bacterium, biologists must create organisms that can
perform a series of complicated functions--namely, when in the bloodstream, they
have to sense and respond to the tumor environment. Once inside the tumor, the
bacteria must infiltrate the cancer cell, and then--and only then--start
producing a tumor-killing toxin. The researchers plan to engineer such
super-organisms by co-opting parts from different types of bacteria and
inserting them into Escherichia coli, a bacterium commonly used in
research. Tumor tissue has unique characteristics, including
lower oxygen and higher lactic acid concentrations than surrounding tissue. To
create a bacterium that can sense a tumor, Christopher Anderson, a postdoctoral
researcher at UCB and UCSF, and colleagues took an oxygen sensor from E. coli
and linked it to a special protein, called invasin, from another type of
bacteria, which allows the organism to invade cancer cells. In a paper published
earlier this year in the Journal of Molecular Biology, the researchers showed in
a test tube that the engineered bacterium selectively invades tumor
cells. Anderson and colleagues are now working on making the
system even more specific. To ensure that the bacteria invade only tumor cells,
they will create a genetic mechanism that allows the invasin protein to be
expressed only when two conditions are met, such as when both the oxygen and
lactic acid concentrations are at a certain level. Essentially, it's a genetic
version of what's known in engineering terms as an AND gate--a regulatory
circuit that's turned on only if two conditions are met. "By
using multiple cues, we can garner a great deal of specificity," says Adam
Arkin, a bioengineer at UCB and the Lawrence Berkeley National Laboratory, a
TR100 recipient in 1999, and one of the senior scientists on the project. "After
the bacteria sense the cues, they turn on the rest of the apparatus to do the
job."
单选题
According to the passage, which of the following statements is NOT
true?
A. A genetic mechanism should be designed to make sure that the invasin
protein is released only when two conditions are met.
B. Tumor tissue has lower oxygen and higher lactic acid concentrations than
surrounding tissue.
C. Research has shown that bacterium loaded with intelligence selectively
invades tumor cells.
D. In terms of targeting cancerous tissues, bacteria is inferior to commonly
applied cancer treatment.
【正确答案】
D
【答案解析】
单选题
Which of the following titles best summarizes the main idea of this
passage?
A. Unique Tumor Tissues
B. Limitations of Conventional Cancer Treatments
C. Tumor-killing Bacteria
D. How Do Bacteria Identify Cancer Cells
【正确答案】
C
【答案解析】
单选题
By quoting "... but bacteria can have sensors and actuators and can
drill into a cell, like a submarine" in paragraph 2, the author indicates that
______.
A. the shape of bacteria is similar with a submarine
B. it is highly possible that bacteria can find the cancerous cells
C. molecules cannot carry sensors and actuators
D. to build a cancer-killing bacterium, scientists must create organisms
that can perform a series of complicated functions
【正确答案】
B
【答案解析】
单选题
All of the following functions can be achieved by cancer-killing
bacteria EXCEPT ______.
A. releasing proteins called invasin
B. drilling into the tumor
C. creating toxins to kill cancerous cells at certain time
D. identifying the unhealthy cells
【正确答案】
A
【答案解析】
单选题
The word "apparatus" in the last sentence of the passage is closest in
meaning to ______.