[求助]置疑大全2772/63-P36-Q5

Passage 36 (36/63)

Protein synthesis begins when the gene encoding a protein is activated. The gene’s sequence of nucleotides is transcribed into a molecule of messenger RNA (mRNA), which reproduces the information contained in that sequence. Transported outside the nucleus to the cytoplasm, the mRNA is translated into the protein it encodes by an organelle known as a ribosome, which strings together amino acids in the order specified by the sequence of elements in the mRNA molecule. Since the 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 to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes.

Biologists once assumed that the variable rates at which cells synthesize different mRNA’s determine the quantities of mRNA’s and their corresponding proteins in a cell. However, recent investigations have shown that the concentrations of most mRNA’s correlate best, not with their synthesis rate, but rather with the equally variable rates at which cells degrade the different mRNA’s in their cytoplasm. If a cell degrades both a rapidly and 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 marrow (bone marrow: n. 骨髓). For red blood cells to accumulate sufficient concentrations of hemoglobin (hemoglobin: n.血色素) (which transports oxygen) to carry out their main function, the cells’ parent cells must simultaneously produce more of the constituent proteins of hemoglobin and less of most other proteins. To do this, the parent cells halt synthesis of non-hemoglobin mRNA’s in the nucleus and rapidly degrade copies of the non-hemoglobin 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 believe that most cells can regulate protein production most efficiently by varying both mRNA synthesis and degradation, as developing red cells do, rather than by just varying one or the other.

Passage 36 (36/63)

Protein（建议这里别翻成什么蛋白质，就是P） synthesis begins when the gene encoding a protein is activated. The gene’s sequence of nucleotides is transcribed into a molecule of messenger RNA (mRNA), which reproduces the information contained in that sequence (这段内容提炼后变成：P合成开始于基因编码，基因序列被值入MRNA分子，还有MRNA的特点). Transported outside the nucleus to the cytoplasm, the mRNA is translated into the protein it encodes by an organelle known as a ribosome, which strings together amino acids in the order specified by the sequence of elements in the mRNA molecule（讲了P被表达的过程，根本没用，过程一点用都没有）. Since the amount（数量来了，关键的东西来了，提高警惕）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（MRNA和P数量相关，所以MRNA控制P合成,是不是比什么过程看起来容易多了，估计ETS也看不懂过程，所以不出题，怕自己也被绕进去）. For example, an excess of certain proteins can cause cells to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes.

Biologists once assumed that the variable rates at which cells synthesize different mRNA’s determine the quantities of mRNA’s and their corresponding proteins in a cell（老观点，MRNA合成决定了P数量）. However, recent investigations have shown that the concentrations of most mRNA’s correlate best, not with their synthesis rate, but rather with the equally variable rates at which cells degrade the different mRNA’s in their cytoplasm(新观点，不但是合成，分解也同样重要的控制P数量). If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNA’s will accumulate to high levels（不论合成快慢，只要分解慢，MRNA或P数量增加）.

An important example of this phenomenon is the development of red blood cells from their unspecialized parent cells in bone marrow (bone marrow: n. 骨髓). For red blood cells to accumulate sufficient concentrations of hemoglobin (hemoglobin: n.血色素) (which transports oxygen) to carry out their main function, the cells’ parent cells must simultaneously produce more of the constituent proteins of hemoglobin and less of most other proteins(现象H增加，没什么用，关键是对现象的解释). To do this, the parent cells halt synthesis of non-hemoglobin mRNA’s in the nucleus and rapidly degrade copies of the non-hemoglobin mRNA’s remaining in the cytoplasm（非H的减少合成，增加分解，合成和分解原来的一起上）. Halting synthesis of mRNA alone would not affect the quantities of proteins synthesized by the mRNA’s still existing in the cytoplasm. Biologists now believe that most cells can regulate protein production most efficiently by varying both mRNA synthesis and degradation, as developing red cells do, rather than by just varying one or the other（这时新观点的总结，合成和分解的一起上）.

5.                 To begin to control a disease caused by a protein deficiency, the passage suggests that a promising experimental treatment would be to administer a drug that would reduce　(控制P少，得合成增加或分解减少或两个都有)

(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(合成和分解都减少恐怕不行，作用抵消了，合成的增加)

(D) the incidence of errors in the transcription of mRNA’s from genetic nucleotide sequences（A）fficeffice" />

(E) the rate of activity of ribosomes in the cytoplasm of most cells

生物文章的读法：

1. GRE,GMAT生物文章如出一辙，大多数讲什么基因，一般也为新老观点对比型．也有反进化论的，我解释的那篇GRE盖世难篇就是．


2. 本人自练了10篇GRE生物文章后，作这种文章一般不错．所以也许方法是管用的．首先生物文章有一堆的生物或基因专有名词，一定马上首字母提炼，否则会被搞死．另外，这些东东之间有一种数量上的联系和表面的表现．要掌握住数量上的比例关系，即A高－＞B低－＞C不变，这很重要，选项就是靠这个绕你，至于导致高低的过程，屁没有用没有，ETS就知道把过程描述的复杂复杂的，重复罗嗦的，绕的你连数量关系都看不出．


3. 下面我来讲讲我作本文的过程，（此文共用时9分钟，做题只用了3分钟全对）．

要增加P, 就要增加P的合成, 还要增加MRNA的分解??是这样吧?

清楚的不能再清楚咯...确实是偶给绕迷糊了, 特别是每次做题做到第4,5题的时候, 脑子特别糊涂. 常常是理解的也会错. 大概是因为给前面很多的错误选项的内容影响了对原文的记忆. 所以阅读作的时候要快, 趁着自己米有忘记的时候作完......

要增加P, 就要增加P的合成, 还要增加MRNA的分解??是这样吧?

MM分解要减少，不是增加

这个还是明天再看吧......现在都迷糊了....

MM别急，只要看看这句话，问题就解决了．别都读了，读多了没什么意思

If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNA’s will accumulate to high levels（不论合成快慢，只要分解慢，MRNA或P数量增加）

一个东东要多，要么合成快，要么分解慢．要么即合成快又分解慢.

嗯, 从新就读这一段, 觉得这些雪茄还真是麻烦, 嗯, 不讨论偶倒是知道, 分解慢的话, 东东当然多. 给他们这么一解释, 就乱七八糟的....

现在是明白咯, INCREASE SYNTHESIS和decrease degradation.

谢谢weiyu, 还好米有给偶弄错大方向

weiyu, 这题我也错了

你所说的我全赞成 可是最后一句话是不是与B相矛盾

Biologists now believe that most cells can regulate protein production most efficiently by varying both mRNA synthesis and degradation, as developing red cells do, rather than by just varying one or the other.

选项B只讲分解慢 没有同时讲分解与合成的关系是不是就跟最后一句话相左右了

另外还有一句

To do this, the parent cells halt synthesis of non-hemoglobin mRNA’s in the nucleus and rapidly degrade copies of the non-hemoglobin mRNA’s remaining in the cytoplasm.

是不是跟B也矛盾

我选的是B  要增加P 就是减少P的合成 增加P的分解  这是根据最后一段红细胞的例子

谢谢