mitotic spindle

Examples of mitotic spindle in the following topics:

• Binary Fission

  • 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.
  • A survey of mitotic assembly components found in present-day unicellular eukaryotes reveals crucial intermediary steps to the complex membrane-enclosed genomes of multicellular eukaryotes.

• The Mitotic Phase and the G0 Phase

  • 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.

• Interphase

  • In order for a cell to move from interphase into the mitotic phase, many internal and external conditions must be met.
  • The two centrosomes will give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis.
  • The cell cycle consists of interphase and the mitotic phase.
  • Interphase is followed by the mitotic phase.
  • During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei.

• Regulation of the Cell Cycle at Internal Checkpoints

  • The G2 checkpoint bars entry into the mitotic phase if certain conditions are not met.
  • If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic cell division.
  • 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.
  • Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.

• Comparing Meiosis and Mitosis

  • The nuclei resulting from a mitotic division are genetically identical to the original nucleus.
  • Chiasmata develop and crossover occurs between homologous chromosomes, which then line up along the metaphase plate in tetrads with kinetochore fibers from opposite spindle poles attached to each kinetochore of a homolog in a tetrad.
  • Meiosis II is much more similar to a mitotic division.
  • During anaphase II and mitotic anaphase, the kinetochores divide and sister chromatids, now referred to as chromosomes, are pulled to opposite poles.

• The Role of the Cell Cycle

  • The cell cycle has two major phases: interphase and the mitotic phase .
  • During the mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides.
  • The cell cycle consists of interphase and the mitotic phase.
  • Interphase is followed by the mitotic phase.
  • During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei.

• Cell Types in Bones

  • As is the case with osteoblasts, osteocytes lack mitotic activity.
  • These osteogenic cells are undifferentiated with high mitotic activity; they are the only bone cells that divide.

• Meiosis II

  • 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.

• Animal Reproduction and Development

  • The process of animal development begins with the cleavage, or series of mitotic cell divisions, of the zygote .
  • During embryonic development, the zygote undergoes a series of mitotic cell divisions, or cleavages, to form an eight-cell stage, then a hollow blastula.

• Meiosis I

  • 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.