AP BIOLOGY

Detailed explanation-1: -Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.

Detailed explanation-2: -The G1 cell cycle checkpoint regulates entry into S phase for normal cells. Components of the G1 checkpoint, including retinoblastoma (Rb) protein, cyclin D1 and p16INK4a, are commonly altered in human malignancies, abrogating cell cycle control.

Detailed explanation-3: -The G1 checkpoint determines whether all conditions are favorable for cell division to proceed. The G1 checkpoint, also called the restriction point (in yeast), is a point at which the cell irreversibly commits to the cell division process.

Detailed explanation-4: -The Cdk is now active and phosphorylates various targets specific to the G1/S transition.

Detailed explanation-5: -M checkpoint – nuclear division setup check It is also called the spindle checkpoint because the cell examines whether all sister chromatids are correctly attached to the spindle microtubules that separate them. If not, the cell pauses mitosis until all sister chromatids have been attached in the right way.