求教大全Passage 14 Q1Q5，实在是疑惑，谢谢大家

aaron22 · 发表于 2013-1-8 19:19:20

看了下论坛，发现自己的疑惑还真是与众不同~~~O(∩_∩)O哈哈~

麻烦各位XDJM帮忙指点下了

Passage 14 (14/63)

Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos. This led them to believe that the cells in the early embryo are undetermined in the sense that each cell has the potential to develop in a variety of different ways. Later biologists found that the situation was not so simple. It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.

A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversibly committed to their fates, and what are the “morphogenetic determinants” that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the debate. Now investigators think they know at least some of the molecules that act as morphogenetic determinants in early development. They have been able to show that, in a sense, cell determination begins even before an egg is fertilized.

Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell; i.e., in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances are inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity.

The substances that Gross studied are maternal messenger RNA’s—products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histones, a class of proteins that bind to DNA. Once synthesized, the histones move into the cell nucleus, where section of DNA wrap around them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histones; the string is the intervening DNA. And it is the structure of these beaded DNA strings that guide the fate of the cells in which they are located.

1.The passage is most probably directed at which kind of audience?

(A) State legislators deciding about funding levels for a state-funded biological laboratory

(B) Scientists specializing in molecular genetics

(C) Readers of an alumni newsletter published by the college that Paul Gross attended

(D) Marine biologists studying the processes that give rise to new species

(E) Undergraduate biology majors in a molecular biology course

答案是E，我选得是B。

我的思路是：最后一段指出全文讨论的物质是一种基因信息素，那么文章的受众不应该是那些学基因学的人吗？

请问大家正确的思路是什么，谢啦

5.Itcan be inferred from the passage that the initial production of histones after an egg is fertilized takes place

(A) in the cytoplasm

(B) in the maternal genes

(C) throughout the protoplasm

(D) in the beaded portions of the DNA strings

(E) in certain sections of the cell nucleus

这题选是选对了，可是真心没谱啊！

Wangsiwei大牛的回答是

原文第三段－Once synthesized, the histones move into the cell nucleus, 前一句－these particular RNA’s direct the synthesis of H,而第二段种说了这个RNA就是located in the cytoplasm of the egg cell说明开始的发生地是C...., 从另一个角度讲，说了是move into the cell nucleus, 说明了开始是在nucleus的外面，第二段说了那个C...就是在nucleus的外面。

但是direct也不一定表明是在一起的呀，还是我钻牛角尖了，谢谢啦

醉清风额 · 发表于 2013-1-14 02:43:57

1.The passage is most probably directed at which kind of audience?

从结构上看，本文开篇讲述了生物学的发展，提到了很多历史事件，而后才提出分子生物学是怎样帮忙解决问题的，并非一开篇就讲分子生物学的相关知识，可以看出本文更偏重于介绍而不是阐述科学研究之类的

从内容上看，本文所涉及的分子生物学知识并没有提到很前沿的相关内容，知识介绍都很浅显，应该不是写给专家看的，可能写这篇文章的是专家。况且并没有通篇讲 molecular genetics

5.Itcan be inferred from the passage that the initial production of histones after an egg is fertilized takes place

醉清风额 · 发表于 2013-1-14 02:57:58

A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversibly committed to their fates, and what are the “morphogenetic determinants” that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the debate. Now investigators think they know at least some of the molecules that act as morphogenetic determinants in early development. They have been able to show that, in a sense, cell determination begins even before an egg is fertilized.

Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell; i.e., in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances are inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity.

The substances that Gross studied are maternal messenger RNA’s—products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histones, a class of proteins that bind to DNA. Once synthesized, the histones move into the cell nucleus, where section of DNA wrap around them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histones; the string is the intervening DNA. And it is the structure of these beaded DNA strings that guide the fate of the cells in which they are located.

morphogenetic determinants = substances = messenger RNA’s （信使RNA ）
而信使RNA很大程度上决定histones的合成
由文章可知morphogenetic determinants = substances in the cytoplasm
因此 histones的合成同样 in the cytoplasm

aaron22 · 发表于 2013-1-14 20:21:30

谢谢，原来定位是substance，恍然大悟啊

文章还是理解不到位啊

laurachen310 · 发表于 2021-10-6 00:41:38

5.Itcan be inferred from the passage that the initial production of histones after an egg is fertilized takes place

(A) in the cytoplasm

(B) in the maternal genes

(C) throughout the protoplasm

(D) in the beaded portions of the DNA strings

(E) in certain sections of the cell nucleus

第五题还是不太懂，文章问的是after an egg is fertilized，但是定位这里说的不是unfertilized吗？“studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell”

求大神解答呀！

求教大全Passage 14 Q1Q5，实在是疑惑，谢谢大家

所属分类: GMAT考试

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求教大全Passage 14 Q1Q5， 实在是疑惑，谢谢大家

所属分类: GMAT考试

正在浏览此版块的会员 ()

求教大全Passage 14 Q1Q5，实在是疑惑，谢谢大家