35.13
Complexo promotor da anáfase
A destruição gradual de proteínas específicas é necessária para a progressão e conclusão do ciclo celular. Essas proteínas são ubiquitinadas pelas ubi…
A conclusão bem-sucedida da anáfase também depende da atividade de uma ubiquitina ligase chamada complexo promotor de anáfase ou ciclossomo APC / C.
Durante a transição para a anáfase, a proteína Cdc20 se liga e ativa a APC/C. O APC/C ativado ubiquitina as proteínas reguladoras, S-ciclinas e M-ciclinas, direcionando-as para degradação proteassômica.
A degradação da ciclina inibe a atividade da maioria dos Cdks. A ausência de atividade quinase dependente de ciclina permite que as fosfatases desfosforilem a maioria dos substratos de Cdk dentro da célula, o que é necessário para a conclusão da anáfase.
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Q1: What is the anaphase promoting complex and what does it do in the cell cycle?
The anaphase promoting complex (APC) is a regulatory protein complex that controls cell cycle progression by targeting proteins for degradation. It acts as a ubiquitin ligase, marking specific proteins with ubiquitin tags that signal their destruction. This degradation is essential for allowing cells to transition through different phases of mitosis and cytokinesis.
Q2: How does the anaphase promoting complex regulate chromatid separation?
The APC controls chromatid separation by degrading proteins that hold sister chromatids together. When APC targets cohesin and securin for destruction, sister chromatids can separate and move to opposite poles of the cell. This degradation is critical for ensuring proper chromosome distribution during anaphase.
Q3: Why is the anaphase promoting complex considered a ubiquitin ligase?
The APC functions as a ubiquitin ligase because it catalyzes the attachment of ubiquitin proteins to target substrates. This ubiquitination marks proteins for degradation by the proteasome. The APC's role as a ubiquitin ligase makes it a key regulatory mechanism for controlling protein levels during cell division.
Q4: What proteins does the anaphase promoting complex target for degradation?
The APC targets multiple proteins essential for maintaining cell cycle checkpoints, including securin and cyclins. Securin degradation allows cohesin cleavage and chromatid separation. Cyclin degradation reduces kinase activity, allowing cells to exit mitosis and progress through the cell cycle phases.
Q5: How does the anaphase promoting complex ensure proper cell cycle regulation?
The APC ensures proper cell cycle regulation by responding to checkpoint signals and degrading proteins at specific times. Its activity is tightly controlled by regulatory proteins and checkpoint mechanisms that prevent premature progression. This temporal regulation guarantees that cells complete one phase before entering the next.
Q6: What happens if the anaphase promoting complex malfunctions during cell division?
If the APC malfunctions, cells may fail to degrade critical regulatory proteins, causing improper chromosome segregation and aneuploidy. Defective APC function can lead to uncontrolled cell division and genomic instability. This dysfunction is associated with cancer development and other cellular disorders.