SAMPLE 13

[醫(yī)學(xué)類]

題目序號(hào)題型歸類

第1題中心主旨題型

第2題審題定位題型

第3題細(xì)節(jié)推導(dǎo)題型

第4題句間關(guān)系題型

第5題細(xì)節(jié)推導(dǎo)題型

Until about five years ago, the very idea that peptide hormones might be made anywhere in the brain besides the hypothalamus was astounding. Peptide hormones, scientists thought, were made by endocrine glands and the hypothalamus was thought to be the brains’ only endocrine gland. What is more, because peptide hormones cannot cross the blood-brain barrier, researchers believed that they never got to any part of the brain other than the hypothalamus, where they were simply produced and then released into the bloodstream.

But these beliefs about peptide hormones were questioned as laboratory after laboratory found that antiserums to peptide hormones, when injected into the brain, bind in places other than the hypothalamus, indicating that either the hormones or substances that cross-react with the antiserums are present. The immunological method of detecting peptide hormones by means of antiserums, however, is imprecise. Cross-reactions are possible and this method cannot determine whether the substances detected by the antiserums really are the hormones, or merely close relatives. Furthermore, this method cannot be used to determine the location in the body where the detected substances are actually produced.

New techniques of molecular biology, however, provide a way to answer these questions. It is possible to make specific complementary DNA’s (c DNA’s) that can serve as molecular probes seek out the messenger RNA’s (mRNA’s) of the peptide hormones. If brain cells are making the hormones, the cells will contain these mRNA’s. If the products the brain cells make resemble the hormones but are not identical to them, then the c DNA’s should still bind to these mRNA’s, but should not bind as tightly as they would to m RNA’s for the true hormones. The cells containing these mRNA’s can then be isolated and their mRNA’s decoded to determine just what their protein products are and how closely the products resemble the true peptide hormones.

The molecular approach to detecting peptide hormones using cDNA probes should also be much faster than the immunological method because it can take years of tedious purifications to isolate peptide hormones and then develop antiserums to them. Roberts, expressing the sentiment of many researchers, states: “I was trained as an endocrinologist. But it became clear to me that the field of endocrinology needed molecular biology input. The process of grinding out protein purifications is just too slow.”

If, as the initial tests with cDNA probes suggest, peptide hormones really are made in brain in areas other than the hypothalamus, a theory must be developed that explains their function in the brain. Some have suggested that the hormones are all growth regulators, but Rosen’s work on rat brains indicates that this cannot be true. A number of other researchers propose that they might be used for intercellular communication in the brain.

1. Which of the following titles best summarizes the text?

[A] Is Molecular Biology the Key to Understanding Intercellular Communication in the Brain?

[B] Molecular Biology: Can Researchers Exploit Its Techniques to Synthesize Peptide Hormones?

[C] The Advantages and Disadvantages of the Immunological Approach to Detecting Peptide Hormones.

[D] Peptide Hormones: How Scientists Are Attempting to Solve Problems of Their Detection and to Understand Their Function?

2. The text suggests that a substance detected in the brain by use of antiserums to peptide hormones may

[A] have been stored in the brain for a long period of time.

[B] play no role in the functioning of the brain.

[C] have been produced in some part of the body other than the brain.

[D] have escaped detection by molecular methods.

3. According to the text, confirmation of the belief that peptide hormones are created in the brain in areas other than the hypothalamus would force scientists to

[A] reject the theory that peptide hormones are made by endocrine glands.

[B] revise their beliefs about the ability of antiserums to detect peptide hormones.

[C] invent techniques that would allow them to locate accurately brain cells that produce peptide hormones.

[D] develop a theory that account for the role played by peptide hormones in the brain.

4. Which of the following is mentioned in the text as a drawback of the immunological method of detecting peptide hormones?

[A] It cannot be used to detect the presence of growth regulators in the brain.

[B] It cannot distinguish between the peptide hormones and substances that are very similar to them.

[C] It uses antiserums that are unable to cross the blood-brain barrier.

[D] It involves a purification process that requires extensive training in endocrinology.

5. The idea that the field of endocrinology can gain from developments in molecular biology is regarded by Roberts with

[A] incredulity.

[B] derision.

[C] indifference.

[D] enthusiasm.

[答案與考點(diǎn)解析]

1. 【答案】D

【考點(diǎn)解析】這是一道中心主旨題。全文從頭至尾討論的是“peptide hormones”在人體內(nèi)產(chǎn)生的部位，所以有關(guān)全文中心主旨內(nèi)容的答案應(yīng)該包含“peptide hormones”。從各段的主題句進(jìn)行分析，第一至四段主要講如何“detect”(探測(cè))肽激素(peptide hormones)所產(chǎn)生的位置，第五段主要講有關(guān)肽激素的“function”。可見本題的正確選項(xiàng)應(yīng)該是D�？忌�在解題時(shí)一定要搞清楚原文所涉及的對(duì)象并且抓住每段的主題句以及它們之間的相互關(guān)系。

2. 【答案】C

【考點(diǎn)解析】這是一道審題定位題。根據(jù)題干中的“a substance detected”可把本題的正確選項(xiàng)迅速確定在第二段的尾句。該句所涉及的核心問(wèn)題是“where”，所以本題的正確選項(xiàng)應(yīng)該是C�？忌�在解題時(shí)一定要迅速而準(zhǔn)確地進(jìn)行審題定位。

3. 【答案】D

【考點(diǎn)解析】本題是一道細(xì)節(jié)推導(dǎo)題。通過(guò)本題題干中的“peptide hormones are created in the brain in areas other than the hypothalamus”可將本題的答案信息來(lái)源迅速確定在尾段的第一句。尾段第一句主要就肽激素的“function”進(jìn)行論述，可見本題的正確選項(xiàng)應(yīng)該是D，選項(xiàng)D中的“role”就等于原文中的“function”�？忌�在解題時(shí)一定要善于抓住主句中的重要信息。

4. 【答案】B

【考點(diǎn)解析】這是一道句間關(guān)系題。根據(jù)本題題干中的“the immunological method”可將本題的答案信息來(lái)源迅速確定在第二段的第二句，而本題的確切答題點(diǎn)在第二段的第三句的后半部分。從第二段第三句的后半部分可以推導(dǎo)出本題的正確答案是B。考生在解題時(shí)一定要注意一般概括句和具體陳述句之間的相互關(guān)系。

5. 【答案】D

【考點(diǎn)解析】本題是一道細(xì)節(jié)推導(dǎo)題。根據(jù)本題題干中的人名“Roberts”可將本題的答案迅速確定在倒數(shù)第二段引號(hào)部分的第二句話，即“But”一詞引導(dǎo)的句子。從該句中的“needed”一詞可以看出本題的正確選項(xiàng)應(yīng)該是D�？忌�在解題時(shí)一定要學(xué)會(huì)深入理解原文的字面含義。

[參考譯文]

肽激素除了下丘腦能制造，在大腦中任何其它的地方都能夠制造。大約五年前僅這一想法本身就是令人驚詫的。科學(xué)家認(rèn)為，肽激素是由內(nèi)分泌腺制造的，而下丘腦被認(rèn)為是大腦中唯一的內(nèi)分泌腺。而且，由于肽激素?zé)o法穿過(guò)血腦障礙，研究人員認(rèn)為它們從不曾到過(guò)除下丘腦以外的大腦任何其它部位，肽激素僅在下丘腦制造出來(lái)，然后被釋放到血管中。

但是關(guān)于肽激素的這種觀點(diǎn)已經(jīng)遭到質(zhì)疑。通過(guò)一次又一次的實(shí)驗(yàn)發(fā)現(xiàn)，肽激素的抗血清一旦被注射到大腦中，它就會(huì)在下丘腦以外的地方粘接起來(lái)。這就說(shuō)明這些地方或是有肽激素存在，或是有與抗血清發(fā)生交叉反應(yīng)的其他物質(zhì)存在。但是，通過(guò)抗血清來(lái)檢驗(yàn)肽激素的免疫學(xué)方法是不精確的。交叉反應(yīng)可能會(huì)發(fā)生，而且以這種手段無(wú)法確認(rèn)用抗血清檢測(cè)的特質(zhì)確實(shí)是肽激素還是僅是與其近似的親緣物質(zhì)。另外，這種方法不能用來(lái)確定被測(cè)物質(zhì)在人體內(nèi)產(chǎn)生的部位。

然而，分子生物學(xué)的新技術(shù)為解決這些問(wèn)題提供了一個(gè)新途徑。科學(xué)家可以制造出一種特別的互補(bǔ)DNA’S (cDNA’s)，作為分子探子查找出肽激素的信使RNA’S (mRNA’s)。如果腦細(xì)胞正在制造肽激素，那么它應(yīng)該包含這些信使RNA’S。如果腦細(xì)胞制造的產(chǎn)品與肽激素相似但并不完全相同，那么這些互補(bǔ)cDAN’S仍然會(huì)和這些信使mRNA’S粘結(jié)，但不會(huì)象和真正肽激素的信使mRNA’S結(jié)合得那么緊密，這些包含信使mRNA’S的細(xì)胞能被分開。研究者可以將信使mRNA’S解碼以確定其蛋白質(zhì)產(chǎn)品究竟是什么及這些產(chǎn)品在多大程度上類似于真正的肽激素。

采用cDAN探子這一分子生物學(xué)方法檢測(cè)肽激素同時(shí)也比免疫學(xué)方法快得多，因?yàn)槿绻�用免疫學(xué)方法，分離肽激素需要幾年枯燥乏味的提純過(guò)程，然后還需培養(yǎng)出他們的抗血清。羅伯茨的一番話表達(dá)了許多研究人員的心聲，他說(shuō)：“我是作為一名內(nèi)分泌學(xué)家接受訓(xùn)練的，但情況對(duì)我來(lái)說(shuō)很清楚，內(nèi)分泌學(xué)領(lǐng)域需要分子生物學(xué)的輸入，靠碾磨來(lái)制造蛋白質(zhì)純化物的過(guò)程實(shí)在是太慢了。”

如果正如用cDNA探子所做的比較初測(cè)試表明的那樣，肽激素確實(shí)是由大腦中下丘腦以外的部位制造出來(lái)的，則有必要建立一套理論來(lái)解釋它們?cè)诖竽X中的作用。某些學(xué)者指出肽激素是生長(zhǎng)調(diào)節(jié)劑，但羅森對(duì)老鼠大腦所作的實(shí)驗(yàn)表明事實(shí)并非如此。很多其它的研究人員指出肽激素或許被用于大腦內(nèi)細(xì)胞與細(xì)胞間的信息傳輸。