第一节 图片判断 在本节中,你将听到10个句子或对话,每个句子或对话配有[A]、[B]、[C]三幅图片。请选择与句子或对话内容相符合的一幅图片,并标在试卷的相应位置。每句话后有15秒钟的停顿,以便选择图片并看下一组图片。每个句子或对话读两遍。 听力原文:The boy runs quickly in order to catch the late bus.
【多选题】How are Cdks stably inactivated in G 1 phase?
A.
During early M phase, when mitosis begins, the cell is awash with active cyclin–Cdk complexes. Those S-Cdks and M-Cdks must be disabled by the end of M phase to allow the cell to complete division and to prevent it from initiating another round of division without spending any time in G 1 .
B.
To usher a cell from the upheaval of M phase to the relative tranquility of G 1 , the cell-cycle control machinery must inactivate its inventory of S-Cdk and M-Cdk.
C.
It does so in several ways: by eliminating all of the existing cyclins, by blocking the synthesis of new ones, and by deploying Cdk inhibitor proteins to muffle the activity of any remaining cyclin–Cdk complexes. The use of multiple mechanisms makes this system of suppression robust, ensuring that essentially all Cdk activity is shut down.
D.
This wholesale inactivation resets the cell-cycle control system and generates a stable G 1 phase, during which the cell can grow and monitor its environment before committing to a new round of division.