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【单选题】
动物由低等向高等发展过程中牙齿的演化特点A.
牙数由
B.
牙形由复杂变为单一同形
C.
牙替换次数由列变为多牙列、列
D.
由端生牙变为侧生牙、槽生牙
E.
由侧生牙变为端生牙、槽生牙
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参考解析：
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皮皮学刷刷变学霸
举一反三
【单选题】患者,男性,46 岁,甲状腺功能亢进,手术治疗后,采取半坐卧位的主要目的是( )
A.
减轻局部出血
B.
预防感染
C.
避免疼痛
D.
有利伤口愈合
E.
改善呼吸困难
【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】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.
【单选题】Cyclic phosphorylation differs from noncyclic phosphorylation in that( )
A.
only cyclic phosphorylation yields NADP
B.
cyclic phosphorylation yields ATP while non-cyclic phosphorylation yields ATP and NADPH
C.
cyclic phosphorylation yields ATP and non-cyclic phosphorylation yields only NADPH
D.
only noncyclic phosphorylation yields ATP
E.
none of the above;there is no difference in end product or in the processes
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