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The Cell Cycle (Purpose of Cell Division, Why is it Important
-Growth,…
The Cell Cycle
Purpose of Cell Division, Why is it Important
-Growth, Repair, Reproduction
Reproduction
- The division of a unicellular organism reproduces an entire organism
Growth and Development
- Central to the development of a multicellular organism
Repair
- Repair and renew cells that die from normal wear and tear, or accidents
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Cell Cycle: Interphase (90% of the time) then M Phase ( Mitotic Phase)
- Go: Not actively undergoing cell division
- G1: Getting ready to divide, growing bigger, expanding, etc
- S: DNA is synthesized and chromosomes are visible, become sister chromatids (2 molecules of DNA, think of chromatids as molecules of DNA )
- G2: Growth and change int cytoplasm ready for the cell to divide (spindle fibers are grown, etc): late interphase. DNA has been replicated, membrane bound nucleus, centrosomes have been replicated
Mitosis and Cytokinesis:
Mitosis: Division of the Nucleus
Cytokinesis: Division of the cytoplasm
Cell Division: Mitosis and cytokinesis- one cell produces two cells genetically equivalent to the parent cell
Mitotic Spindle:
- Centrosome and Microtubules
- Aster: At the individual pole
Kinetochores:
- Proteins associated with DNA at the centromere
- Present on each sister chromatid ( the kinetochores of the joined sister chromatids face in opposite direction)
- spindle fibers attached during prometaphase
Proteins holding sister chromatids together inactive and/or degraded
- allows separate chromatids move to opposite poles
At which end does it shortened? Microtubules in association with chromosomes are the ones shortening it. Chromosome movement is believe, through motor proteins, the movement towards the pole.
Non-Kinetochore Microtubules:
Legnthen cell alon the axis defined by the pole
- Overlap at the metaphse
- During anaplahse less overlap as motor proteins push microtubles away from each other
- addition of new tubulin monomers extends their length
- lengthen cells
What exactly occurs during mitosis?Prophase
- Chromosomes condense
- Chromosomes appear as sister chromatids joined at centromere
- Nucleoli disappear
- Mitotic spindle begins to form
- Spindle pushes the centrosomes to poles of the cells
Prometaphase
- Nuclear envelope fragments
- Microtubules from spindle interact with the chromosomes at one of two kinetochores
Metaphase
- Spindle fibers aligned chromosomes at metaphase plate
Anaphase
- Microtubules shorten and separate chromatids to form complete chromosomes
Telophase
- Two daughter nuceli form, surrounded by the framents of the parent's nuclear
- Chromatin Decondenses
- Nucleoli reappear
- Cytokinesis Begins
Cytokinesis:
Animal Cells
- Division of the cytoplasm
- Begins with formation of cleavage furrow
- Cytoplasmic side of cleavage furrow contractile ring pinches the cell in two
Plant Cells: Cannot do that because of the cell wall
- Cell plate forms during telophase (vesicles) to form cell wall (form cell membrane and cell wall)
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