AP BIOLOGY

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THE CELL

CELL COMMUNICATION

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Which of these may be assessed by various proteins during a “checkpoint”? CHECK ALL THAT APPLY
A
Ensure that all chromosomes have lined up in the center of the cell before sister chromatids separate
B
Ensure that spindle fibers have attached to all centromeres before cell division
C
Ensure that DNA has been replicated properly
Explanation: 

Detailed explanation-1: -Checkpoint proteins, such as PD-L1 on tumor cells and PD-1 on T cells, help keep immune responses in check. The binding of PD-L1 to PD-1 keeps T cells from killing tumor cells in the body (left panel).

Detailed explanation-2: -Cell cycle checkpoints are surveillance mechanisms that monitor the order, integrity, and fidelity of the major events of the cell cycle. These include growth to the appropriate cell size, the replication and integrity of the chromosomes, and their accurate segregation at mitosis.

Detailed explanation-3: -The cell cycle is controlled at three checkpoints. The integrity of the DNA is assessed at the G1 checkpoint. Proper chromosome duplication is assessed at the G2 checkpoint. Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.

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