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Few areas of neurobehavioral research seemed more promising in the early sixties than that investigating the relationship between protein synthesis and learning. The conceptual framework for this research was derived directly from molecular biology, which had shown that genetic information is stored in nucleic acids and expressed in proteins. Why not acquired information as well?
The first step toward establishing a connection between protein synthesis and learning seemed to be to block memory (cause amnesia) by interrupting the production of proteins. We were fortunate in finding a nonlethal dosage of puromycin that could, it first appeared, thoroughly inhibit brain protein synthesis as well as reliably produce amnesia.
Before the actual connection between protein synthesis and learning could be established, however, we began to have doubts about whether inhibition of protein synthesis was in fact the method by which puromycin produced amnesia. First other drugs, glutarimides—themselves potent protein-synthesis inhibitors—either failed to cause amnesia in some situations where it could easily be induced by puromycin or produced an amnesia with a different time course from that of puromycin. Second puromycin was found to inhibit protein synthesis by breaking certain amino-acid chains, and the resulting fragments were suspected of being the actual cause of amnesia in some cases. Third, puromycin was reported to cause abnormalities in the brain including seizures. Thus, not only were decreased protein synthesis and amnesia dissociated, but alternative mechanisms for the amnestic action of puromycin were readily suggested
So, puromycin turned out of be a disappointment. It came to be regarded as a poor agent for amnesia studies, although, of course, it was poor only in the context of our original paradigm of protein-synthesis inhibition. In our frustration, our initial response was simply to change drugs rather than cur conceptual orientation. After many such disappointments, however, it now appears unlikely that we will make a firm connection between protein synthesis and learning merely by pursuing the approaches of the past. Our experience with drugs has shown that all the amnestic agents often interfere with memory in ways that seem unrelated to their inhibition of protein synthesis, More importantly, the notion that the interruption or intensification of protein production in the brain can be related in cause-and-effect fashion to learning now seems simplistic and unproductive. Remove the battery from a car and the car will not go. Drive the car a long distance at high speed and the battery will become more highly charged. Neither of these facts proves that the battery powers the car only a knowledge of the overall automotive system will reveal its mechanism of locomotion and the role of the battery within that system.
The primary purpose of the passage is to
A.The primary purpose of the passage is to
B.argue that genetic engineering promises to lead to even higher yields than are achievable with synthetic fertilizers
C.argue that the capacity for nitrogen- fixing symbioses is transferable to nonleguminous plants
D.explain the reasons for and the objectives of current research on nitrogen-fixing symbioses
E.describe the nature of the genes that regulated they symbiosis between legumes and certain bacteria
According to the passage, there is currently no strain of Rhizobium that can enter into a symbiosis with
A.alfalfa
B.clover
C.maize
D.peas
E.soybeans
The passage implies that which of the following is true of the bacterial genus Rhizobium?
A.Rhizobium bacteria are found primarily in nitrogen-depleted soils.
B.Some strains of Rhizobium are not capable of entering into a symbiosis with any plant.
C.Newly bred varieties of legumes cannot be hosts to any strain of Rhizobium.
D.Rhizobium bacteria cannot survive outside the protected habitat provided by host plants.
E.Rhizobium bacteria produce some ammonia their own purposes.
It can be inferred from the passage that which of the following was the most influential factor in bringing about intensified research on nitrogen fixation?
A.The high yields of the Green Revolution
B.The persistent upward surge in natural gas prices
C.The variety of Rhizobium strains
D.The mechanization of modern agriculture
E.The environmental ill effects of synthetic fertilizers
Which of the following situations is most closely analogous to the situation described by the author as one of nature's great ironies (lines 37-42)?
A.That of a farmer whose crops have failed because the normal midseason rains did not materialize and no preparations for irrigation had been made
B.That of a long-distance runner who loses a marathon race because of a wrong turn that cost him twenty seconds
C.That of shipwrecked sailors at sea in a lifeboat, with one flask of drinking water to share among them
D.That of a motorist who runs out of gas a mere five miles from the nearest gas station
E.That of travelers who want to reach their destination as fast and as cheaply as possible, but find that cost increases as travel speed increases
According to the passage, the ultimate goal of the current research on nitrogen fixation is to develop
A.strains of Rhizobium that can enter into symbioses with existing varieties of wheat, rice, and other nonlegnumes
B.strains of Rhizobium that produce more ammonia for leguminous host plants than do any of the strains presently known
C.varieties of wheat, rice, and other nonlegumes that yield as much as do existing varieties, but require less nitrogen
D.arieties of wheat, rice, and other nonlegumes that maintain an adequate symbiotic relationship with nitrogen-fixing bacteria and produce high yields
E.high-yielding varieties of wheat, rice, and other nonlegumes that are genetically equipped to fix nitrogen from the air without the aid of bacteria
The author regards the research program under discussion as
A.original and extensive but ill-defined as to method
B.necessary and ambitious but vulnerable to failure
C.cogent and worthwhile but severely under-funded
D.prohibitively expensive but conceptually elegant
E.theoretically fascinating but practically useless
Most nearly parallel, in its fundamental approach, to the research program described in the passage would be a program designed to
A.achieve greater frost resistance in frost- tender food plants by means of selective breeding, thereby expanding those plants' area of cultivation
B.achieve greater yields from food plants by interplanting crop plants that are mutually beneficial
C.find inexpensive and abundant natural substances that could, without reducing yields, be substituted for expensive synthetic fertilizers
D.change the genetic makeup of food plants that cannot live in water with high salinity, using genes from plants adapted to salt water
E.develop, through genetic engineering, a genetic configuration for the major food plants that improves the storage characteristics of the edible portion of the plants
