Cell Division - Mitosis: Difference between revisions

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==Some Recent Findings==
== Some Recent Findings ==
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==Movies==
==Movies==

Revision as of 09:17, 20 April 2011

Introduction

Mitosis and meiosis

Normal cell division in all cells, except germ cells, occurs by 2 mechanical processes that initially divide the nucleus then the cell cytoplasm.

  • Mitosis segregation of chromosomes and formation of 2 nuclei
  • Cytokinesis splitting of the cell as a whole into 2 daughter cells
Cell Division Links: meiosis | mitosis | Lecture - Cell Division and Fertilization | spermatozoa | oocyte | fertilization | zygote | Genetics

Some Recent Findings

Movies

<wikiflv height= width="400" height="388" autostart="true" repeat="true" logo="false">Mitosis 01.flv|File:Mitosis 01 icon.jpg</wikiflv>

Mitosis Movie[2] See also: Movie - Mitosis

Links: MCB Movie - The stages of mitosis and cytokinesis in an animal cell

Cell Changes

  • Nucleus
    • Chromosome condensation
    • Nuclear envelope breakdown
  • Cytoplasm
    • Cytoskeleton reorganization
    • Spindle formation (MT) Contractile ring (MF)
    • Organelle redistribution
  • Mitosis Energy
    • Cell division uses up a lot of energy, so cells ensure they have enough resources to complete the job before committing to it.

Mitosis Phases

  • Based on light microscopy of living cells light and electron microscopy of fixed and stained cells
  • 5 Phases - prophase, prometaphase, metaphase, anaphase, and telophase
    • Cytokinesis 6th stage overlaps the end of mitosis

MBC The stages of mitosis and cytokinesis in an animal cell


Interphase

  • not a mitotic phase (discussed in cell cycle)
  • Chromosomes dispersed in nucleus
  • Gene expression
  • Cytoskeleton and cell organelles - Distributed and functioning
  • Mitochondria undergo independent proliferation/division

Chromosome Changes

Mitosis fl.jpg

Prophase

Mammalian cell - prophase[3]
  • Chromosome DNA has been earlier duplicated (S Phase)
  • Chromosomes begin condensing
  • Chromosome pairs (chromatids) held together at centromere
  • Microtubules disassemble
  • Mitotic spindle begins to form

Spindle Apparatus

  • 3 sets of microtubules - (+) ends point away from centrosome at each pole.
  1. astral microtubules - anchor the pole end in position
  2. kinetochore microtubules - connected to chromosomes
  3. polar microtubules - form the structure of the spindle apparatus

Spindle Apparatus EM | Spindle Apparatus | MBC Movie- Microtubule dynamics during mitosis

At end of prophase nuclear envelope breaks down

Prometaphase

  • Microtubules now enter nuclear region
  • Nuclear envelope forms vesicles around mitotic spindle
  • Kinetochores form on centromere attach to some MTs of spindle

Dynamic instability and the capture of chromosomes

Centromeric attachment of microtubules

At end of prometaphase chromosomes move to metaphase plate

Metaphase

Mitosis - Metaphase
  • Kinetochore MTs align chromosomes in one midpoint plane

Proposed alternative mechanisms for chromosome congression

Metaphase ends when sister kinetochores separate

Anaphase

Chromosome motility anaphase
  • Separation of sister Kinetochores
  • shortening of Kinetochore microtubules pulls chromosome to spindle pole

Experiment - during anaphase A chromosomes move poleward along stationary kinetochore microtubules, which coordinately disassemble from their kinetochore ends

Anaphase ends as nuclear envelope (membrane) begins to reform

Telophase

Mitosis - Telophase
  • Chromosomes arrive at spindle poles
  • Kinetochore MTs lost
  • Condensed chromosomes begin expanding
    • Continues through cytokinesis

Links: Figure 19-41 Microtubule dynamics during mitosis | Figure 19-34. The stages of mitosis and cytokinesis in an animal cell | Cytokinetic abscission: cellular dynamics at the midbody

Cytokinesis

  • Division of cytoplasmic contents
  • Contractile ring forms at midpoint under membrane
  • Microfilament ring - contracts forming cleavage furrow
    • myosin II is the motor
  • Eventually fully divides cytoplasm

Links: Cytokinesis | Cytokinesis in Plants

Cell Organelles

Mitochondria

  • Divide independently of cell mitosis
  • distributed into daughter cells

Peroxisomes

  • localise at spindle poles

Endoplasmic Reticulum

Golgi

File:Post-mitotic Golgi stack formation.png
Post-mitotic Golgi stack formation
  • 2 processes - disassembly and reassembly[4]
  • Golgi stack undergoes a continuous fragmentation process
  • fragments are distributed into daughter cells
  • are reassembled into new Golgi stacks

Disassembly

  • Unstacking - mediated by two mitotic kinases (cdc2 and plk)
  • Vesiculation - mediated by COPI budding machinery ARF1 and the coatomer complex

Reassembly

  • Fusion - formation of single cisternae by membrane fusion
  • Restacking - requires dephosphorylation of Golgi stacking proteins by protein phosphatase PP2A

References

  1. <pubmed></pubmed>
  2. <pubmed>12105179</pubmed>
  3. Russan NM. Let's Build a Spindle. ASCB Image & Video Library. 2008;CYT-190. Available at: http://cellimages.ascb.org/u?/p4041coll12,521
  4. <pubmed>18156178</pubmed>

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Additional Images



Cite this page: Hill, M.A. (2024, April 19) Embryology Cell Division - Mitosis. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Mitosis

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G