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搜题
【单选题】
艾滋病最常见的机会性感染是A.
口腔念珠菌病
B.
卡氏肺孢子虫肺炎
C.
外阴部疱疹病毒感染
D.
疱疹性直肠炎
E.
巨细胞病毒性视网膜炎
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参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】If c is a codeword of a (n,k) cyclic code, the (n-k)-bit cyclic shift on c toward left gives .
A.
a redundent word .
B.
another codeword in this cyclic code
C.
another redundent word.
D.
the same codeword in this cyclic code
【简答题】环式电子传递(cyclic electron transport)
【简答题】环化核苷酸(cyclic nudeotide)
【多选题】LTE系统业务信道有哪几种cyclic prefix格式（）。
A.
Normal cyclic prefix
B.
Abnormal cyclic prefix
C.
Standard cyclic prefix
D.
Extended cyclic prefix
【多选题】How do GPCRs regulate intracellular cyclic AMP levels?
A.
Many extracellular signals acting via GPCRs affect the activity of the enzyme adenylyl cyclase and thus alter the intracellular concentration of the second messenger molecule cyclic AMP.
B.
Most commonly, the activated G protein α subunit switches on the adenylyl cyclase, causing a dramatic and sudden increase in the synthesis of cyclic AMP from ATP.
C.
To help terminate the signal, a second enzyme, called cyclic AMP phosphodiesterase, rapidly converts cyclic AMP to ordinary AMP. Cyclic AMP phosphodiesterase is continuously active inside the cell. Because it eliminates cyclic AMP so quickly, the cytosolic concentration of this second messenger can change rapidly in response to extracellular signals, rising or falling tenfold in a matter of seconds.
D.
Cyclic AMP is water-soluble, so it can, in some cases, carry the signal throughout the cell, traveling from the site on the membrane where it is synthesized to interact with proteins located in the cytosol, in the nucleus, or on other organelles. One way that caffeine acts as a stimulant is by inhibiting this phosphodiesterase in the nervous system, blocking cyclic AMP degradation and thereby keeping the concentration of this second messenger high.
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