The Function Of The Apc/c Is To Trigger Which Phase Of Mitosis?

**The function of the APC/C is to trigger the metaphase to anaphase transition in mitosis.** Mitosis is the process by which a cell divides its genetic material into two daughter cells. It consists of several distinct phases, including prophase, prometaphase, metaphase, anaphase, and telophase. Each phase is regulated by specific molecular mechanisms to ensure accurate and controlled cell division.

The Anaphase-Promoting Complex/Cyclosome (APC/C) is a key player in the regulation of the metaphase to anaphase transition. It is a multi-subunit E3 ubiquitin ligase complex that targets specific proteins for degradation via the ubiquitin-proteasome pathway. In this article, we will explore the function of the APC/C in triggering the metaphase to anaphase transition, its composition, and its role in maintaining cell cycle control.

APC/C: The Gatekeeper of Metaphase to Anaphase Transition

The metaphase to anaphase transition is a critical point in the cell cycle, where sister chromatids, the replicated DNA strands, are separated and pulled towards opposite poles of the cell. The proper timing and coordination of this transition are vital to ensure accurate distribution of genetic material. The APC/C plays a central role in controlling this transition by regulating the degradation of key cell cycle regulators.

1. Regulation of Anaphase-Promoting Complex/Cyclosome Activity

The activity of the APC/C is tightly regulated throughout the cell cycle to ensure its precise timing and function. The APC/C is activated by the protein Cdc20 in late metaphase and early anaphase. Cdc20 binds to the APC/C, facilitating the recruitment of specific substrate proteins and their subsequent ubiquitination and degradation. In addition to Cdc20, another protein called Cdh1 can also activate the APC/C in late mitosis and G1 phase.

2. Substrate Proteins Targeted by the APC/C

The APC/C targets several key proteins for degradation during the metaphase to anaphase transition. One of the primary substrates of the APC/C is a protein called securin. Securin plays a crucial role in preventing premature sister chromatid separation by inhibiting a protein complex called separase. The APC/C marks securin for degradation, which releases separase, allowing it to cleave a protein called cohesin that holds sister chromatids together. This cleavage promotes the separation of sister chromatids and progression into anaphase.

Another important substrate of the APC/C is a protein called cyclin B1. Cyclin B1 forms complexes with cyclin-dependent kinase 1 (CDK1) to regulate the progression of the cell cycle. The APC/C targets cyclin B1 for degradation, leading to the inactivation of CDK1 and the subsequent exit from mitosis.

3. Control of Cell Cycle Checkpoints

The APC/C also plays a role in the regulation of cell cycle checkpoints, which are surveillance mechanisms that ensure the integrity of DNA replication and chromosome segregation. By degrading specific proteins, the APC/C helps to prevent the premature progression of the cell cycle in the presence of DNA damage or other abnormalities.

For example, the APC/C targets a protein called Wee1 kinase for degradation during the G2/M checkpoint. Wee1 kinase phosphorylates and inactivates CDK1, thereby preventing the entry into mitosis. By degrading Wee1 kinase, the APC/C promotes the activation of CDK1 and the progression into mitosis.

Frequently Asked Questions

Q: How is the APC/C complex composed?

The APC/C is a large macromolecular complex composed of multiple subunits. It consists of at least 13 core subunits, including APC1-APC13, which form the catalytic core responsible for ubiquitin ligase activity. Additionally, regulatory subunits such as Cdc20 and Cdh1 bind to the APC/C to activate or inhibit its activity, depending on the stage of the cell cycle.

Q: Are there any diseases associated with APC/C dysfunction?

Yes, APC/C dysfunction has been implicated in various diseases, including cancer. Dysregulation of the APC/C can lead to abnormal cell cycle progression, genomic instability, and uncontrolled cell division. Mutations or alterations in the genes encoding APC/C subunits or its regulators have been observed in certain types of cancer, highlighting the importance of proper APC/C function in maintaining cellular homeostasis.

Q: Are there any drugs targeting the APC/C?

Given the critical role of the APC/C in cell cycle control, it has emerged as a potential target for anticancer therapies. Researchers are actively exploring the development of drugs that can modulate the activity of the APC/C or specifically inhibit its function in cancer cells. However, targeted therapies against the APC/C are still at an early stage of development, and further research is needed to evaluate their efficacy and safety.

Final Thoughts

The APC/C is a crucial player in the regulation of the metaphase to anaphase transition in mitosis. By targeting specific proteins for degradation, the APC/C ensures accurate chromosome segregation and proper cell division. Understanding the function and regulation of the APC/C provides valuable insights into the fundamental processes that govern cell cycle progression and may have implications for the development of novel therapeutic approaches in the future.

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