12.2. Mitosis and Cytokinesis Flashcards
Chromosome condensation…
DNA is tightly packed into nucleosomes (DNA is wrapped around histones).
Before mitosis, nucleosomes become supercoiled and cannot be accessed by proteins involved in replication or transcription.
The chromosomes become visible through a light microscope.
Chromosome segregation…
Mediated by the mitotic spindle.
This consists of two centrosomes, with each centrosome consisting of a pair of centrioles. There are two due to duplication during the S phase.
Microtubules extend from these centrioles:
- Polar: connect the two centrosomes, therefore stabilise the structure.
- Kinetochore microtubules: connect to the chromosome at the kinetochores on the chromosomes. This actually pulls them apart.
The condensed chromosomes attach to microtubules.
The microtubule pulls the chromosomes apart.
The phases of mitosis…
(Details not required)…
Prophase.
Prometaphase.
Metaphase.
Anaphase.
Telophase.
Cytokinesis.
Prophase…
DNA condenses and supercoils.
The two centrosomes move to opposite sides of the cell to become spindle poles.
Prometaphase…
The nuclear envelope breaks down.
Extending microtubules can now attach to the chromosomes at the kinetochores.
Metaphase…
Chromosomes align along the metaphase plate (the cell’s equator).
Anaphase…
Spindle poles begin to pull the sister chromatids apart.
They move towards the spindle poles.
Telophase…
The chromatids reach the spindle poles.
The nuclear membranes reform around the chromosomes.
Cytokinesis…
The cell then undergoes the physical separation of two cells.
In animal cells, this is driven by the contraction of an actomyosin ring.
This pinches the daughter cells and separates them.
In plant cells, a new cell wall is constructed inside the cell, in between the two daughter cells.
Vesicles fuse to form a cell plate between the two cells.
