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SAT官方每日一 bf9 附答案和解析[阅读](2019年1月21日)

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Critical Reading>Select an Answer

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 build 5a9 ing 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 __________

A.consenting.
B.fulfilling.
C.permitting.
D.transferring.

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重点单词   查看全部解释    
bond [bɔnd]

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n. 债券,结合,粘结剂,粘合剂
vt. 使结

 
membrane ['membrein]

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n. 薄膜,膜皮,羊皮纸

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context ['kɔntekst]

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n. 上下文,环境,背景

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block [blɔk]

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n. 街区,木块,石块
n. 阻塞(物), 障

 
cell [sel]

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n. 细胞,电池,小组,小房间,单人牢房,(蜂房的)巢室

 
selectivity [silek'tiviti]

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n. 选择性;分离性;选择度

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component [kəm'pəunənt]

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n. 元件,组件,成份
adj. 组成的,构成

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contrast ['kɔntræst 346 ,kən'træst]

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n. 差别,对比,对照物
v. 对比,成对照<

 
exclusive [iks'klu:siv]

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568

adj. 独占的,唯一的,排外的
n. 独家新

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opera ['ɔpərə]

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n. 歌剧
n. 挪威Opera软件公司的浏览

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X
单词opera 联想记忆:
a和o结尾的都是艺术单词,源于意大利
 


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