Examples of spindle checkpoint in the following topics:
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- The M checkpoint is also known as the spindle checkpoint because it determines whether all the sister chromatids are correctly attached to the spindle microtubules.
- Because the separation of the sister chromatids during anaphase is an irreversible step, the cycle will not proceed until the kinetochores of each pair of sister chromatids are firmly anchored to at least two spindle fibers arising from opposite poles of the cell.
- The cell cycle is controlled at three checkpoints.
- The integrity of the DNA is assessed at the G1 checkpoint.
- Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.
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- In addition to the internally controlled checkpoints, there are two groups of intracellular molecules that regulate the cell cycle.
- Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.
- The different cyclins and Cdks bind at specific points in the cell cycle and thus regulate different checkpoints.
- For the cell to move past each of the checkpoints, all positive regulators must be "turned on" and all negative regulators must be "turned off."
- There is a direct correlation between cyclin accumulation and the three major cell cycle checkpoints.
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- For example, a mutation that allows the Cdk gene to be activated without being partnered with cyclin could push the cell cycle past a checkpoint before all of the required conditions are met.
- In addition to the cell cycle regulatory proteins, any protein that influences the cycle can be altered in such a way as to override cell cycle checkpoints.
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- The precise timing and formation of the mitotic spindle is critical to the success of eukaryotic cell division.
- Prokaryotic cells, on the other hand, do not undergo karyokinesis and, therefore, have no need for a mitotic spindle.
- However, the FtsZ protein that plays such a vital role in prokaryotic cytokinesis is structurally and functionally very similar to tubulin, the building block of the microtubules that make up the mitotic spindle fibers that are necessary for eukaryotes.
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- This discovery is not surprising in light of the multiple roles that the p53 protein plays at the G1 checkpoint.
- Essentially, without a fully functional p53, the G1 checkpoint is severely compromised and the cell proceeds directly from G1 to S regardless of internal and external conditions.
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- Microtubules that will eventually form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen.
- The mitotic spindle continues to develop as more microtubules assemble and stretch across the length of the former nuclear area.
- The proteins of the kinetochore attract and bind mitotic spindle microtubules.
- The mitotic spindles are depolymerized into tubulin monomers that will be used to assemble cytoskeletal components for each daughter cell.
- During prometaphase, mitotic spindle microtubules from opposite poles attach to each sister chromatid at the kinetochore.
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- The centrosomes that were duplicated during interphase I move away from each other toward opposite poles and new spindles are formed.
- The nuclear envelopes are completely broken down and the spindle is fully formed.
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- The centrosomes, which are the structures that organize the microtubules of the meiotic spindle, also replicate.
- The key event in prometaphase I is the formation of the spindle fiber apparatus where spindle fiber microtubules attach to the kinetochore proteins at the centromeres.
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- There are many internal checkpoints that monitor a cell's health; if abnormalities are observed, a cell can spontaneously initiate the process of apoptosis.
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- The two centrosomes will give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis.