|Embryology - 9 May 2021 Expand to Translate|
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Mitosis is the form of cell division in all cells, except germ cells, occurs by 2 mechanical processes that initially divide the nucleus then the cell cytoplasm. Each mitosis of a diploid cell produces 2 diploid cells. Historically, the cells produced by this division are called "daughter" cells.
- Mitosis segregation of chromosomes and formation of 2 nuclei
- Cytokinesis splitting of the cell as a whole into 2 daughter cells
See main page Mitosis
Meiosis is a special type of "reductive" cell division occurring only in the generation of germ cells. Reductive because it produces from the original double genome copy (diploid) a single copy (haploid) of the cell nuclear genome. The mechanism is the same in male and female, though it differs substantially as to when it occurs and how many germ cells are produced from each original diploid cell.
- female - (oocyte, egg) formed before birth, only a single haploid cell is produced, meiosis is only completed in the uterus at fertilization.
- male - (spermatozoa, sperm) formed after puberty, four haploid cells are produced, meiosis is completed in the testis.
See main page Meiosis
- Cell Division Milestones
- Recent Nobel Prizes- 2001 Cell Cycle, 2002 Cell Death
|Cell Division Links: meiosis | mitosis | Lecture - Cell Division and Fertilization | spermatozoa | oocyte | fertilization | zygote | Genetics|
Some Recent Findings
|More recent papers|
This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
Search term: Cell division
Search term: Mitosis
Search term: Meiosis
The labelling allows you to see the chromosomes and the linking region (kinetochore) between chromosome pairs and the mitotic spindle microtubules.
Final part of movie shows the two cells in bright field illumination.
- Chromosome condensation
- Nuclear envelope breakdown
- 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.
- 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
- 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 DNA has been earlier duplicated (S Phase)
- Chromosomes begin condensing
- Chromosome pairs (chromatids) held together at centromere
- Microtubules disassemble
- Mitotic spindle begins to form
- 3 sets of microtubules - (+) ends point away from centrosome at each pole.
- astral microtubules - anchor the pole end in position
- kinetochore microtubules - connected to chromosomes
- polar microtubules - form the structure of the spindle apparatus
At end of prophase nuclear envelope breaks down
- Microtubules now enter nuclear region
- Nuclear envelope forms vesicles around mitotic spindle
- Kinetochores form on centromere attach to some MTs of spindle
At end of prometaphase chromosomes move to metaphase plate
- Kinetochore MTs align chromosomes in one midpoint plane.
- Astrin is a spindle-associated protein required for chromosome alignment at the metaphase plate.
Metaphase ends when sister kinetochores separate
- Separation of sister Kinetochores
- shortening of Kinetochore microtubules pulls chromosome to spindle pole.
- Katanin is a microtubule-severing complex involved with this stage of microtubule dynamics.
Anaphase ends as nuclear envelope (membrane) begins to reform.
- Chromosomes arrive at spindle poles
- Kinetochore MTs lost
- Condensed chromosomes begin expanding
- Continues through 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
- Divide independently of cell mitosis
- distributed into daughter cells
- localise at spindle poles
- 2 processes - disassembly and reassembly
- Golgi stack undergoes a continuous fragmentation process
- fragments are distributed into daughter cells
- are reassembled into new Golgi stacks
- Unstacking - mediated by two mitotic kinases (cdc2 and plk)
- Vesiculation - mediated by COPI budding machinery ARF1 and the coatomer complex
- Fusion - formation of single cisternae by membrane fusion
- Restacking - requires dephosphorylation of Golgi stacking proteins by protein phosphatase PP2A
- Russan NM. Let's Build a Spindle. ASCB Image & Video Library. 2008;CYT-190. Available at: http://cellimages.ascb.org/u?/p4041coll12,521
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Cite this page: Hill, M.A. (2021, May 9) Embryology Cell Division. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division
- © Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G