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【简答题】
我上海某公司向美国一公司出售货物一批，出口总价为2万美元CIF纽约，其中从上海到纽约的海运运费为2500美元，按CIF总值的120%投保一切险，保险费率为5%，这批货物的国内进价及各种费用加总为10万元人民币。试计算这笔货物贸易的出口换汇成本。
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【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
【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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