请教og-5-28RNA和histone是什么关系？

那位NN帮忙解答，拜谢了！

og-5-28:

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

(5) 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

(10) 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

(15) 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

(20) 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 o show that,

in a sense, cell determination begins even before an egg

(25) is fertilized.

Studying sea urchins, biologist Paul Gross found

that an unfertilized egg contains substances that func-

tion as morphogenetic determinants. They are located

in the cytoplasm of the egg cell; i.e., in that part of the

(30) 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

(35) 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

(40) 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

(45) histones move into the cell nucleus, where section of

DNA wrap around them to form a structure that resem-

bles 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

(50) DNA strings that guides the fate of the cells in which

they are located.

28. It can 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（A）

(E)   in certain sections of the cell nucleus

28.

A is the best answer. In the third paragraph, the author asserts that substances that function as

morphogenetic determinants are located in the cytoplasm of the cell and become active after the

cell is fertilized. In the fourth paragraph we learn that these substances are “maternal messenger

RNA’s” and that they “direct, in large part, the synthesis of histones,” which, after being

synthesized, “move into the cell nucleus” (lines 59-68). Thus, it can be inferred that after the egg

is fertilized, the initial production of histones occurs in the cytoplasm.

文章说substanceare located in the cytoplasm of the egg cell; i.e., in that part of the cell’s protoplasm that lies outside of the nucleus，

然后又说The substances that Gross studied are maternal messenger RNA’s

接下来these particular RNA’s direct, in large part, the synthesis of histones,

再下来 Once synthesized, the histones move into the cell nucleus, 

如果选A的话，小弟不太理解。我觉得substance应该是RNA，而RNA direct（指导？不知对不对？）histones的合成。

而文章说的是substance，也就是RNA存在于cytoplasm中，怎么就能得出histones存在于cytoplasm中呢？

不知小弟的逻辑存在什么问题，请NN指正！谢谢啦！

接下来these particular RNA’s direct, in large part, the synthesis of histones,

再下来 Once synthesized, the histones move into the cell nucleus, 

如果选A的话，小弟不太理解。我觉得substance应该是RNA，而RNA direct（指导？不知对不对？）histones的合成。

而文章说的是substance，也就是RNA存在于cytoplasm中，怎么就能得出histones存在于cytoplasm中呢？

不知小弟的逻辑存在什么问题，请NN指正！谢谢啦！

Once synthesized, the histones move into the cell nucleus

而问题问的是initial products,所以在h move之前,h应该在cytoplasm中

对不起，这题我做的是云里雾里，而且对生物确实知识太少。

难道move into nucleus，除了从cytoplasm以外，就没有其他可能的来源了么？

文章说是RNA存在于cytoplasm，很难得出histones也在cytoplasm中阿？

多谢！

请看l42-43

these particular RNA’s direct, in large part, the synthesis of histones

文中已经明确说了二者的关系

抱歉，我觉得楼上的兄弟的解释还无法回答这个问题啊。。。。。。。我也有这个疑问。。。请大家帮忙解答。

楼主问得是：

难道move into nucleus，除了从cytoplasm以外，就没有其他可能的来源了么？

文章说是RNA存在于cytoplasm，很难得出histones也在cytoplasm中阿？

RNA direct（指导？不知对不对？）histones的合成。

我的确是找不到确切的能从文章里显示出的证据哦。。。。。。。。。