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Step-by-Step Explanation
Step 1: Context of the Anaphase Promoting Complex (APC)
The cell cycle is divided into different phases (G1, S, G2, and M), and the mitotic (M) phase includes prophase, metaphase, anaphase, and telophase. During anaphase, sister chromatids separate and move towards opposite poles of the cell. The Anaphase Promoting Complex (APC) is a crucial protein complex that regulates this process by targeting specific proteins for degradation.
Step 2: Role of APC During Anaphase
APC functions primarily by adding ubiquitin groups to certain regulatory proteins, marking them for destruction by the proteasome. A key target is the protein known as securin, which inhibits separase. When securin is degraded, separase becomes active and cleaves the cohesin complexes holding sister chromatids together. This action allows the chromatids to separate and move to opposite poles (segregation).
Step 3: Consequence of a Defective APC
If APC is defective, it can no longer ubiquitinate securin effectively. As a result, separase remains inactive because securin is not destroyed. Therefore, sister chromatids remain attached to each other, and proper chromosome segregation fails to occur during anaphase. This defect ultimately disrupts the normal distribution of genetic material into the daughter cells.
Step 4: Reasoning Behind the Correct Answer
Given the options, the most direct outcome of APC malfunction is that chromosomes do not segregate (they fail to move apart). This matches the correct choice which states “Chromosomes will not segregate.”
Step 5: Concluding Remarks
The integrity of cell division relies heavily on APC to initiate the separation of chromosomes. Any impairment of APC compromises the anaphase process, leading to errors in chromosome distribution that can have significant and detrimental consequences for the cell.
