SAT阅读不间断练习：Like an opera house

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Like an opera house, which has its public entrance separate from that for the performers, a cell has different doors for different molecules. Each gets scrutinized at its door before it can enter the cell. Now researchers from the University of California at San Francisco have revealed in the journal Science the three-dimensional structure of one such door, or membrane channel, that specializes in granting entry to a membrane component known as glycerol. Specifically the channel is called the glycerol facilitator (GlpF), from the bacterium Escherichia coli.

Bearing three alcohol groups, glycerol is a basic building block for the cell membrane. (Other components include fatty acids and small charged molecules.) And not just in E. coli. Indeed, although the channel the researchers studied is from a bacterium, it belongs to a large protein family dubbed the aquaporins, which are found in species ranging from bacteria to humans.

GlpF is highly specific for glycerol and similar polyalcohols. Somehow, even though water molecules are much smaller, they cannot enter. The new study reveals why. In order for glycerol to clear the four-channel configuration in the cell membrane, it must pass through a narrow selectivity filter in the center of a channel. Here it is surrounded by amino acids that closely match its own structure, which is hydrophilic ("water-loving") on one side and hydrophobic ("water-fearing") on the other. Water molecules, in contrast, can only pass through this area in single file, which is not energetically favorable, because they like to bond to one another. And ions, which are charged, are unable to pass the "water-fearing" side of the channel. This cell entrance, it seems, is truly exclusive.

The underlined word "granting" most nearly means __________

与granting意思最接近的单词是

A. consenting.

B. fulfilling.

C. permitting.

D. transferring.

答案：C

解析：

Choice C is the best answer. The context makes it clear that when the author says the membrane channel specializes in "granting entry to a membrane component," she means that the membrane channel's job is to permit entry to the membrane component, or to allow the membrane component to move into the cell.

SAT阅读每日一练推荐词汇

context['kɔntekst]n. 上下文，环境，背景

alcohol['ælkəhɔl]n. 酒精，乙醇，酒

species['spi:ʃiz]n. (单复同)物种，种类

component[kəm'pəunənt]n. 元件，组件，成份 adj. 组成的

membrane['membrein]n. 薄膜，膜皮，羊皮纸联想记忆

exclusive[iks'klu:siv]adj. 独占的，唯 一的，排外的

bacterium[bæk'tiəriəm]n. 细菌 bacteria[bæk'tiəriə]n. (复数)细菌

selectivity[silek'tiviti]n. 选择性;分离性;选择度联想记忆

favorable['feivərəbl]adj. 有利的，赞许的，良好的，顺利的，偏袒的

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