Telophase in Cell Division
Telophase is the final stage of cell division in eukaryotic cells, crucial for the proper segregation of chromosomes and the re-establishment of cellular structures. It involves the decondensation of chromosomes, reassembly of the nuclear envelope, and disassembly of the mitotic spindle. Molecular mechanisms like the dephosphorylation of proteins by phosphatases, such as Cdc14 in yeast, and the degradation of cyclins by the APC/C are key for transitioning from mitosis to cytokinesis. Additional regulatory proteins like Cdc48/p97 also play a significant role in telophase progression.
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Understanding Telophase in Cell Division
Telophase represents the concluding phase of cell division in eukaryotic cells, completing the processes of mitosis and meiosis. It is characterized by the re-establishment of the cell's normal structures after the chromosomal separation of earlier stages. Chromosomes, having been segregated to opposite poles of the cell, begin to decondense into chromatin. The nuclear envelope reassembles around each set of chromosomes, and nucleoli re-form within the new nuclei. The mitotic spindle, composed of microtubules that played a crucial role in chromosome separation, is disassembled, with its components being recycled for future use. Telophase is a short but critical phase, occupying approximately 2% of the cell cycle's duration, and sets the stage for the subsequent process of cytokinesis.The Transition from Telophase to Cytokinesis
Cytokinesis is the division of the cytoplasm that results in the formation of two distinct daughter cells, and it often initiates while telophase is still underway. The coordination between telophase and cytokinesis ensures that each daughter cell receives an equal and complete set of genetic material along with the necessary cellular organelles. This transition is essential for the maintenance of genetic stability and cell function, as it culminates the process of cell division by physically separating the two daughter nuclei into individual cells.Molecular Mechanisms Regulating Telophase
The orderly progression through telophase is governed by complex molecular mechanisms, including the dephosphorylation of proteins previously phosphorylated by mitotic cyclin-dependent kinases (Cdks). The phosphorylation of these substrates by M-Cdks is crucial for initiating mitotic events such as spindle formation, chromosome condensation, and nuclear envelope breakdown. The subsequent dephosphorylation signals the disassembly of the spindle, the decondensation of chromosomes, and the reformation of the nuclear envelope. The transition from phosphorylation to dephosphorylation is facilitated by the inactivation of Cdks through the proteolytic degradation of their cyclin partners by the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase. This degradation, commencing in anaphase, is vital for the cell's progression into telophase.The Role of Phosphatases in Telophase
Phosphatases are crucial in telophase as they reverse the phosphorylation of Cdk substrates, enabling the cell to exit mitosis. In the model organism Saccharomyces cerevisiae, or budding yeast, the phosphatase Cdc14 is essential for this transition. Inhibition of Cdc14 activation results in a cell cycle arrest similar to that caused by the failure to degrade M-cyclins, highlighting the importance of phosphatase activity in conjunction with cyclin degradation for successful cell cycle progression through telophase.Reconsidering the Passive Nature of Anaphase and Telophase
Anaphase and telophase were once considered passive phases that occurred after the spindle-assembly checkpoint was satisfied, allowing the transition from metaphase to anaphase. However, emerging research indicates that these phases may involve additional, active checkpoints. For example, the regulation of Cdc14 phosphatase activity differs between anaphase and telophase, suggesting more sophisticated control mechanisms. Cdc14 is released from the nucleolus and exported to the cytoplasm, with its full release and sustained activity being essential for the disassembly of the spindle apparatus and the reassembly of the nuclear envelope.Additional Mechanisms Driving Telophase
In addition to the shift in phosphorylation states, a variety of regulatory mechanisms contribute to the initiation of telophase. The physical separation of chromosomes from the metaphase plate during anaphase may provide cues for the onset of telophase. Proteins such as Cdc48 in yeast (and its human homolog, p97) are also critical for the progression of telophase. These proteins use ATPase activity to change the conformation of other proteins, aiding in spindle disassembly, nuclear envelope reformation, and chromosome decondensation. Cdc48/p97 also targets certain ubiquitinated proteins for proteasomal degradation, further illustrating the complex regulation of telophase.Want to create maps from your material?
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1
During telophase, chromosomes that were previously separated start to transform back into ______.
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2
The ______ envelope reforms around each group of chromosomes, signaling the end of telophase.
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3
The mitotic ______, essential for chromosome separation, is broken down and its parts are saved for later use.
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4
Telophase is brief, making up about ______% of the cell cycle's total time, and prepares the cell for cytokinesis.
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5
Cytokinesis definition
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6
Cytokinesis initiation timing
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7
Cytokinesis and genetic stability
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8
The transition from ______ to ______ is aided by the inactivation of Cdks, which is achieved by the degradation of cyclins via the ______.
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9
During mitosis, the ______ of proteins by M-Cdks is essential for processes like spindle assembly, ______ condensation, and the breakdown of the ______ envelope.
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10
Role of Cdc14 in yeast cell cycle
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11
Consequence of Cdc14 inhibition
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12
Phosphatase and cyclin degradation synergy
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13
______ and ______ were traditionally seen as inactive stages following the spindle-assembly checkpoint, leading to the progression from ______ to ______.
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14
The activity of ______ phosphatase is regulated differently during ______ and ______, hinting at complex control processes.
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15
Cdc14 is liberated from the ______ and moves to the ______, a crucial step for the dismantling of the ______ and the reconstruction of the ______ ______.
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16
Role of chromosome separation in telophase initiation
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17
Function of Cdc48/p97 in telophase
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18
Cdc48/p97 and proteasomal degradation
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