There was a sudden gust of wind and ____.

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.

conservative means being opposed to great or sudden change.()

冠状动脉性猝死(sudden coronary death)(名词解释)

A.sugar

B. sudden

C. surprise

D. Saturday

It ______ came to her that she had been wrong all the time. (sudden)

The sudden vowel shift in the history of English helped to shape ________ English.

A.Old

B.Middle

C.Early Modern

D.Late Modern

A.Visible

B.Occasional

C.Actual

D.Gradual

In a sudden ______ of anger，the man tore up everything within reach.

A) attackB) burstC) splitD)