• 科普:“鹊桥”中继星靠什么帮“嫦娥”赴广寒 2020-02-27
  • 嘉实资本陶荣辉:在不确定性中寻找确定性机会 2020-02-27
  • 2000多家国企医院年底前完成剥离 2020-02-19
  • 文瀛公园第二届百合花展 2020-02-16
  • 在红色传承中加速绿色崛起 2020-02-16
  • (受权发布)全国人民代表大会常务委员会任命名单 2020-02-16
  • 支持创新企业发行股票或存托凭证试点 证监会发布四项相关文件 2020-02-16
  • 青海100个最美观景拍摄点 2020-02-12
  • 尧都农商银行全力推进服务“三农”工作 2020-02-12
  • 河南一矿企收33张罚单仍违法排污 有基层官员站台 2020-02-12
  • 《大国小鲜》两会特辑第六期:中美新能源“争夺战” 2020-02-12
  • 南昌首个婴儿岛何时开放 探访南昌弃婴救助机制 2020-02-11
  • 北京12.4万人申报积分落户 初核结果7月31日后公布 2020-02-08
  • 办个房产证,也要惊动省委书记? 2020-02-08
  • 《大国小鲜》两会特辑第六期:中美新能源“争夺战” 2020-01-30
  • 手机APP下载

    您现在的位置: 第一百五十期码报 > SAT > SAT每日一题 > 正文

    SAT官方每日一题附答案和解析[阅读](2019年10月18日)

    来源:可可英语 编辑:max ?  VIP免费外教试听课 |  可可官方微信:ikekenet

    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 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 main purpose of the passage is to __________

    A.explain the ways proteins function in various species.
    B.analyze and argue against a common claim about bacteria.
    C.assert that a new research technique will enhance future studies in the field of cellular biology.
    D.discuss a study that offers a new understanding of a fundamental cellular process.

    重点单词   查看全部解释    
    enhance [in'hɑ:ns]

    想一想再看

    vt. 提高,加强,增加

     
    bacteria [bæk'tiəriə]

    想一想再看

    n. (复数)细菌

     
    opera ['ɔpərə]

    想一想再看

    n. 歌剧
    n. 挪威Opera软件公司的浏览

    联想记忆
    channel ['tʃænl]

    想一想再看

    n. 通道,频道,(消息)渠道,海峡,方法
    v

    联想记忆
    favorable ['feivərəbl]

    想一想再看

    adj. 有利的,赞许的,良好的,顺利的,偏袒的

     
    certain ['sə:tn]

    想一想再看

    adj. 确定的,必然的,特定的
    pron.

     
    separate ['sepəreit]

    想一想再看

    n. 分开,抽印本
    adj. 分开的,各自的,

     
    alcohol ['ælkəhɔl]

    想一想再看

    n. 酒精,乙醇,酒

     
    function ['fʌŋkʃən]

    想一想再看

    n. 功能,函数,职务,重大聚会
    vi. 运行

     
    claim [kleim]

    想一想再看

    n. 要求,要求权;主张,断言,声称;要求物

     
    ?
    发布评论我来说2句

      最新文章

      可可英语官方微信(微信号:ikekenet)

      每天向大家推送短小精悍的英语学习资料.

      添加方式1.扫描上方可可官方微信二维码。
      添加方式2.搜索微信号ikekenet添加即可。
    • 科普:“鹊桥”中继星靠什么帮“嫦娥”赴广寒 2020-02-27
    • 嘉实资本陶荣辉:在不确定性中寻找确定性机会 2020-02-27
    • 2000多家国企医院年底前完成剥离 2020-02-19
    • 文瀛公园第二届百合花展 2020-02-16
    • 在红色传承中加速绿色崛起 2020-02-16
    • (受权发布)全国人民代表大会常务委员会任命名单 2020-02-16
    • 支持创新企业发行股票或存托凭证试点 证监会发布四项相关文件 2020-02-16
    • 青海100个最美观景拍摄点 2020-02-12
    • 尧都农商银行全力推进服务“三农”工作 2020-02-12
    • 河南一矿企收33张罚单仍违法排污 有基层官员站台 2020-02-12
    • 《大国小鲜》两会特辑第六期:中美新能源“争夺战” 2020-02-12
    • 南昌首个婴儿岛何时开放 探访南昌弃婴救助机制 2020-02-11
    • 北京12.4万人申报积分落户 初核结果7月31日后公布 2020-02-08
    • 办个房产证,也要惊动省委书记? 2020-02-08
    • 《大国小鲜》两会特辑第六期:中美新能源“争夺战” 2020-01-30
    • 球探比分即时棒球比分直播 连码专家六俏复式图片 黑龙江体育彩票 吉林十一选五走势图 一码中特的网站 体彩20选5走势图浙江风采网 24足球比分十分感激! 闲来麻将下载手机版 重庆时时彩又赚钱的嘛 浙江20选5走势图