2.1.6 Cell cycle - Mitosis Flashcards
How is DNA packaged?
DNA is wrapped around histone proteins to form chromatin. Chromatin is coiled around more proteins to form chromosomes.
What is the structure of chromosomes?
Before replication each chromosome is in the form of long, thin chromatin, that densely coils and folds during replication. Each duplicated chromosome has two sister chromatids, which are joined copies of the original chromosome. The two sister chromatids are joined together at a region called the centromere.
What happens during prophase?
During prophase, chromatid fibres begin to coil and condense to form chromosomes which become visible. The nucleus, responsible for RNA synthesis, disappears and the nuclear membrane starts to breakdown. Each duplicated chromosome appears as two identical sister chromatids joined at their centromere. The mitotic spindle begins to develop from each centrosome as protein microtubules extend out of them.
What happens during Prometaphase?
During Prometaphase, the two centrosomes migrate to opposite poles, partly propelled by the lengthening microtubules between them. The nuclear envelope fragments in prometaphase. The microtubules invade the nuclear area as they extend from each centrosome. The chromosomes condense further, and microtubules attach to (the kinetochore of) each centromere.
What happens during Metaphase?
During Metaphase, the chromosomes are moved by the spindle fibres to form the metaphase plate in the centre of the cell. The centrosomes are now at the poles of the cell. The chromosomes convene at the metaphase plat which is equidistance between the spindle poles. The centromeres are at the end of this plate lined upon the equator. By metaphase, the microtubules of the asters have also grown and are in contact with the plasma membrane.
What happens during Anaphase?
During Anaphase, the cohesion proteins are cleaved, causing the centromeres to divide. This allows the two sister chromatids of each pair to part suddenly, becoming a fully-fledged chromosome. Chromatids move to the poles of the cell centromere the “v-shape’, at the rate of 1 μm/min.
What happens during Telophase?
During Telophase, two daughter nuclei form in the cell. Nuclear envelopes arise from fragments of the parent cell’s envelope. The nucleus forms and reappears in each envelope. The chromosomes become less condensed and remaining spindle fibres are depolymerised. Cytokinesis begins with the division of the two cells.
Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.
How does cytokinesis occur in animal cells?
In Animal Cells cytokinesis involves the formation of a cleavage furrow, which pinches the cell into two. The cleavage furrow is a contractile ring of actin microfilaments.
How does cytokinesis occur in plant cells?
Due to cell walls, cleavage furrows are not possible in plant cells.
In plant cells vesicles assemble where the metaphase plate was formed and fuse to form a cell plate that divides the cell.
Vesicles produced by the Golgi body collect on equator of cell. These vesicle fuse to form a cell plate. In plant cells vesicles assemble where the metaphase plate was formed and fuse to form a cell plate that divides the cell.
