6.2 - Mitosis Flashcards
Define mitosis
Nuclear division in the mitotic phase of the cell cycle
- Ensures 2 identical daughter cells (diploid)
Who is mitosis for?
Mitosis is critical for asexual reproduction in plants, fungi and some animals,
not prokaryotes, they reproduce asexually, but by binary fission
What are chromosomes and chromatids?
Chromosomes - coiled and condensed DNA ready for division
Chromatids - 2 identical copies of a chromosome (DNA) held by a centromere (1 chromosome is converted into 2 chromatids)
1 chromosome > 2 chromatids per chromosome (after replication) > 1 chromatid (after mitotic division)
What are the roles of centromeres?
Necessary to ensure chromatids stay together, are precisely manouvred and segregated equally.
How can you practically view mitosis?
- Using plant root tips (meristems)
1) Treat root tips with chemical to separate cells
2) Place on squash slide
3) Use DNA binding stain to make chromosomes visible
What occurs during prophase?
1) Chromatin fibres (complex of proteins DNA and RNA) coil and condense to form chromosomes. Nucleolus breaks down and nuclear membrane begins to degrade.
2) Protein microtubules form spindle fibres, which are used to move chromosomes into correct positions
3) Centrioles migrate to opposite poles of the cell - cylindrical bundles of protein which help spindle formation
4) Spindle fibres attach to centromere and begin to move chromosomes
5) Nuclear envelope disintegrates by end of prophase.
What occurs during metaphase?
Metaphase plate forms
- Chromosomes moved by spindle fibres to form plane across the cell
What occurs during the anaphase?
Chromatids separate as centromeres holding chromosomes together divide - they are pulled to opposite poles of the cell by shortening the spindle fibres
- The V-shape appears as centromere drags chromatids through liquid cytosol.
What occurs during the telophase?
- Chromatids reach poles - now called chromosomes
- New set of chromosomes assemble at each pole
- 2 new nuclear envelopes form
What occurs during cytokinesis?
In animal cells
- Actual division of cytoplasm forming new cells
1) Cleavage furrows from in middle of cell
2) Plasma membrane pulled inwards by cytoskeleton, until close enough to fuse and form 2 new cells - Microfilament ring around the centre of the 2 cless contracts (contractile fibres) and splits the cells.
How does cytokinesis occur in plant cells?
- Presence of cell wall makes it impossible for cleavage furrow formation
1) Vesicles from GA assemble where metaphase plate equatior was
2) Vesicles fuse, dividing cell into 2
3) New cell wall sections formed where membranes split.
What would happen if the cell dividing cell wall formed before the cells separate?
It would undergo osmotic lysis.
