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【单选题】
在 里,共有27 个 收音,但收音的 实际发 音只有 个。A.
5
B.
6
C.
7
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反馈参考答案：
举一反三
【简答题】--- How about the book you are reading? --- Good indeed. It many problems we have come across in our study. A. says B. talks C. covers D. refers
【单选题】B195 . 下列家庭投资理财方式中,风险和收益都按照从低到高顺序排列的是
A.
企业债券、 国债、股票
B.
股票、企业债券、国债
C.
国债、企业债券、股票
D.
股票、国债、企业债券
【多选题】How do G proteins work?
A.
There are several varieties of G proteins. Each is specific for a particular set of receptors and for a particular set of target enzymes or ion channels in the plasma membrane. All of these G proteins, however, have a similar general structure and operate in a similar way. They are composed of three protein subunits—α, β, and γ—two of which are tethered to the plasma membrane by short lipid tails.
B.
In the unstimulated state, the α subunit has GDP bound to it, and the G protein is idle.
C.
When an extracellular signal molecule binds to its receptor, the altered receptor activates a G protein by causing the α subunit to decrease its affinity for GDP, which is then exchanged for a molecule of GTP. In some cases, this activation breaks up the G-protein subunits, so that the activated α subunit, clutching its GTP, detaches from the βγ complex, which is also activated.
D.
The two activated parts of the G protein—the α subunit and the βγ complex—can then each interact directly with target proteins in the plasma membrane, which in turn may relay the signal to other destinations in the cell. The longer these target proteins remain bound to an α subunit or a βγ complex, the more prolonged the relayed signal will be.
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