AP BIOLOGY

Detailed explanation-1: -The G1 checkpoint. The G1 checkpoint is located at the end of G1 phase, before the transition to S phase. If cells don’t pass the G1 checkpoint, they may “loop out” of the cell cycle and into a resting state called G0, from which they may subsequently re-enter G1 under the appropriate conditions.

Detailed explanation-2: -The G1 Checkpoint The cell will only pass the checkpoint if it is an appropriate size and has adequate energy reserves. At this point, the cell also checks for DNA damage. A cell that does not meet all the requirements will not progress to the S phase.

Detailed explanation-3: -The G1/S cell cycle checkpoint controls the passage of eukaryotic cells from the first gap phase (G1) into the DNA synthesis phase (S). Two cell cycle kinases, CDK4/6-cyclin D and CDK2-cyclin E, and the transcription complex that includes Rb and E2F are pivotal in controlling this checkpoint.

Detailed explanation-4: -During G1 phase, growth-dependent cyclin-dependent kinase (CDK) activity promotes DNA replication and initiates G1-to-S phase transition. CDK activation initiates a positive feedback loop that further increases CDK activity, and this commits the cell to division by inducing genome-wide transcriptional changes.

Detailed explanation-5: -The G1 checkpoint, also known as the restriction point in mammalian cells and the start point in yeast, is the point at which the cell becomes committed to entering the cell cycle.