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Passage 36
  Protein synthesis begins when the gene1 encoding a protein is activated2. The gene‘s sequence of nucleotides is transcribed3 into a molecule4 of messenger RNA (mRNA),which reproduces the information contained in that(5) sequence. Transported outside the nucleus5 to the cyto-plasm,the mRNA is translated into the protein it encodes by an organelle known as a ribosome, which strings6 together amino acids in the order specified7 by the sequence of elements in the mRNA molecule. Since the(10)amount of mRNA in a cell determines the amount of the corresponding protein, factors affecting the abundance of mRNA’s play a major part in the normal functioning of a cell by appropriately regulating protein synthesis. For example, an excess of certain proteins can cause cells(15) to proliferate8 abnormally and become cancerous; a lack of the protein insulin results in diabetes9.
  Biologists once assumed that the variable rates at which cells synthesize different mRNA‘s determine the  quantities of mRNA’s and their corresponding proteins(20) in a cell. However, recent investigations11 have shown that the concentrations of most mRNA‘s correlate best, not with their synthesis rate, but rather with the equally vari-able rates at which cells degrade the different mRNA’s in their cytoplasm. If a cell degrades both a rapidly and(25) a slowly synthesized mRNA slowly, both mRNA‘s will accumulate to high levels.
  An important example of this phenomenon is the development of red blood cells from their unspecialized parent cells in bone marrow13. For red blood cells to accu-(30)mulate sufficient concentrations of hemoglobin (which transports oxygen) to carry out their main function, the cells‘ parent cells must simultaneously14 produce more of the constituent15 proteins of hemoglobin and less of most other proteins. To do this, the parent cells halt synthesis(35) of nonhemoglobin mRNA’s in the nucleus and rapidly degrade copies of the nonhemoglobin mRNA‘s remaining  in the cytoplasm. Halting synthesis of mRNA alone would not affect the quantities of proteins synthesized by the mRNA’s still existing in the cytoplasm. Biologists now(40) believe that most cells can regulate protein production most efficiently16 by varying both mRNA synthesis and degradation17, as developing red cells do, rather than by just varying one or the other.

  1. The passage is primarily concerned with discussing the
   (A) influence of mRNA concentrations on the development of red blood cells
   (B) role of the synthesis and degradation of mRNA in cell functioning
   (C) mechanism18 by which genes19 are transcribed into mRNA
   (D) differences in mRNA concentrations in cell nuclei20 and in the cytoplasm
   (E) way in which mRNA synthesis contributes to the onset21 of diabetes

  2. The passage suggests that a biologist who held the view described in the first sentence of the second paragraph would most probably also have believed which of the following?
   (A) The rate of degradation of specific mRNA‘s has little effect on protein concentrations.
   (B) The rate of degradation of specific mRNA‘s should be studied intensively.
   (C) The rates of synthesis and degradation for any given mRNA are normally equal.
   (D) Different mRNA‘s undergo degradation at widely varying rates.
   (E) Most mRNA‘s degrade very rpaidly.

  3. Which of the following best describes the relationship between the second and third paragraphs of the passage?
   (A) The second paragraph presents arguments in support of a new theory and the third paragraph presents arguments against that same theory.
   (B) The second paragraph describes a traditional view and the third paragraph describes the view that has replaced it on the basis of recent investigations.
   (C) The third paragraph describes a specific case of a phenomenon that is described generally in the second paragraph.
   (D) The third paragraph describes an investigation10 that was undertaken to resolve problems raised by phenomena22 described in the second paragraph.
   (E) Both paragraphs describe in detail specific examples of the phenomenon that is introduced in the first paragraph.

  4. The accumulation of concentrations of hemoglobin in red blood cells is mentioned in the passage as an example of which of the following?
   (A) The effectiveness of simultaneous variation of the rates of synthesis and degradation of mRNA
   (B) The role of the ribosome in enabling a parent cell to develop properly into a more specialized12 form
   (C) The importance of activating23 the genes for particular proteins at the correct moment
   (D) The abnormal proliferation of a protein that threatens to make the cell cancerous
   (E) The kind of evidence that biologists relied on for support of a view of mRNA synthesis that is now considered obsolete24

  5. To begin to control a disease caused by a protein deficiency, the passage suggests that a promising25 experimental treatment would be to administer a drug that would reduce
   (A) only the degradation rate for the mRNA of the protein involved
   (B) only the synthesis rate for the mRNA of the protein involved
   (C) both the synthesis and degradation rates for the mRNA of the protein involved
   (D) the incidence of errors in the transcription of mRNA‘s from genetic26 nucleotide sequences
   (E) the rate of activity of ribosomes in the cytoplasm of most cells

  6. According to the passage, which of the following best describes the current view on the relationship between the synthesis and the degradation of mRNA in regulating protein synthesis?
   (A) Biologists have recently become convinced that the ribosome controls the rates of synthesis and degradation of mRNA.
   (B) There is no consensus27 among biologists as to the significance of mRNA degradation in regulating protein synthesis.
   (C) The concept of mRNA degradation is so new that most biologists still believe that the vital role in protein regulation belongs to mRNA synthesis.
   (D) Degradation of mRNA is now considered to be the key process and mRNA synthesis is no longer believed to play a significant role.
   (E) Degradation of mRNA is now considered to be as important as mRNA synthesis has been, and still is,believed to be.

  7. According to the passage, which of the following can happen when protein synthesis is not appropriately regulated?
   (A) Diabetes can result from errors that occur when the ribosomes translate mRNA into protein.
   (B) Cancer can result from an excess of certain proteins and diabetes can result from an insulin deficiency.
   (C) A deficiency of red blood cells can occur if bone marrow cells produce too much hemoglobin.
   (D) Cancer can be caused by excessively rapid degradation of certain amino acids in the cytoplasm of cells.
   (E) Excessive synthesis of one protein can trigger increased degradation of mRNA‘s for other proteinsand create severe protein imbalances.

  8. The passage suggests that a biologist who detected high levels of two proteins in a certain type of cell would be likely to consider which of the following as a possible explanation?
   (A) The rate of mRNA degradation for one of the proteins increases as this type of cell develops a more specialized function.
   (B) The two proteins are most likely constituents28 of a complex substance supporting the cells‘ specialized function.
   (C) The cells are likely to proliferate abnormally and possibly become cancerous due to the levels of these proteins.
   (D) The mRNA‘s for both proteins are being degraded at a low rate in that type of cell.
   (E) The mRNA‘s for the two proteins are being synthesized at identical rates in that type of cell.


1 gene     
  • A single gene may have many effects.单一基因可能具有很多种效应。
  • The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。
2 activated     
adj. 激活的 动词activate的过去式和过去分词
  • The canister is filled with activated charcoal.蒸气回收罐中充满了活性炭。
3 transcribed     
(用不同的录音手段)转录( transcribe的过去式和过去分词 ); 改编(乐曲)(以适应他种乐器或声部); 抄写; 用音标标出(声音)
  • He transcribed two paragraphs from the book into his notebook. 他把书中的两段抄在笔记本上。
  • Every telephone conversation will be recorded and transcribed. 所有电话交谈都将被录音并作全文转写。
4 molecule     
  • A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈?f婘??妈?成的。
  • This gives us the structural formula of the molecule.这种方式给出了分子的结构式。
5 nucleus     
  • These young people formed the nucleus of the club.这些年轻人成了俱乐部的核心。
  • These councils would form the nucleus of a future regime.这些委员会将成为一个未来政权的核心。
6 strings     
  • He sat on the bed,idly plucking the strings of his guitar.他坐在床上,随意地拨着吉他的弦。
  • She swept her fingers over the strings of the harp.她用手指划过竖琴的琴弦。
7 specified     
  • The architect specified oak for the wood trim. 那位建筑师指定用橡木做木饰条。
  • It is generated by some specified means. 这是由某些未加说明的方法产生的。
8 proliferate     
  • We must not proliferate nuclear arms.我们决不能扩散核武器。
  • Rabbits proliferate when they have plenty of food.兔子有充足的食物就会繁衍得很快。
9 diabetes     
  • In case of diabetes, physicians advise against the use of sugar.对于糖尿病患者,医生告诫他们不要吃糖。
  • Diabetes is caused by a fault in the insulin production of the body.糖尿病是由体內胰岛素分泌失调引起的。
10 investigation     
  • In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
  • He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。
11 investigations     
(正式的)调查( investigation的名词复数 ); 侦查; 科学研究; 学术研究
  • His investigations were intensive and thorough but revealed nothing. 他进行了深入彻底的调查,但没有发现什么。
  • He often sent them out to make investigations. 他常常派他们出去作调查。
12 specialized     
  • There are many specialized agencies in the United Nations.联合国有许多专门机构。
  • These tools are very specialized.这些是专用工具。
13 marrow     
  • It was so cold that he felt frozen to the marrow. 天气太冷了,他感到寒冷刺骨。
  • He was tired to the marrow of his bones.他真是累得筋疲力尽了。
14 simultaneously     
  • The radar beam can track a number of targets almost simultaneously.雷达波几乎可以同时追着多个目标。
  • The Windows allow a computer user to execute multiple programs simultaneously.Windows允许计算机用户同时运行多个程序。
15 constituent     
  • Sugar is the main constituent of candy.食糖是糖果的主要成分。
  • Fibre is a natural constituent of a healthy diet.纤维是健康饮食的天然组成部分。
16 efficiently     
  • The worker oils the machine to operate it more efficiently.工人给机器上油以使机器运转更有效。
  • Local authorities have to learn to allocate resources efficiently.地方政府必须学会有效地分配资源。
17 degradation     
  • There are serious problems of land degradation in some arid zones.在一些干旱地带存在严重的土地退化问题。
  • Gambling is always coupled with degradation.赌博总是与堕落相联系。
18 mechanism     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
19 genes     
n.基因( gene的名词复数 )
  • You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因,所以能够活得很长。 来自《简明英汉词典》
  • Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪
20 nuclei     
  • To free electrons, something has to make them whirl fast enough to break away from their nuclei. 为了释放电子,必须使电子高速旋转而足以摆脱原子核的束缚。
  • Energy is released by the fission of atomic nuclei. 能量是由原子核分裂释放出来的。
21 onset     
  • The drug must be taken from the onset of the infection.这种药必须在感染的最初期就开始服用。
  • Our troops withstood the onset of the enemy.我们的部队抵挡住了敌人的进攻。
22 phenomena     
  • Ade couldn't relate the phenomena with any theory he knew.艾德无法用他所知道的任何理论来解释这种现象。
  • The object of these experiments was to find the connection,if any,between the two phenomena.这些实验的目的就是探索这两种现象之间的联系,如果存在着任何联系的话。
23 activating     
  • "I didn't say we'd got to stop activating the masses! “我并没说就此不发动! 来自子夜部分
  • Presumably both the very small size and activating influence of fluorine atoms contribute to this exception. 这大概是由于氟原子半径小和活性高这两个原因的影响,氟原子对这种例外做出了贡献。
24 obsolete     
  • These goods are obsolete and will not fetch much on the market.这些货品过时了,在市场上卖不了高价。
  • They tried to hammer obsolete ideas into the young people's heads.他们竭力把陈旧思想灌输给青年。
25 promising     
  • The results of the experiments are very promising.实验的结果充满了希望。
  • We're trying to bring along one or two promising young swimmers.我们正设法培养出一两名有前途的年轻游泳选手。
26 genetic     
  • It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
  • Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。
27 consensus     
  • Can we reach a consensus on this issue?我们能在这个问题上取得一致意见吗?
  • What is the consensus of opinion at the afternoon meeting?下午会议上一致的意见是什么?
28 constituents     
n.选民( constituent的名词复数 );成分;构成部分;要素
  • She has the full support of her constituents. 她得到本区选民的全力支持。
  • Hydrogen and oxygen are the constituents of water. 氢和氧是水的主要成分。 来自《简明英汉词典》