Mitosis stages Flashcards
Name the stages of Mitosis.
Prophase, Metaphase, Anaphase, Telophase.
What happens in Prophase?
Chromosomes condense & become visible whilst the nuclear membrane disintegrates. Centrioles move to opposite pole ends of the nucleus & mitotic spindles grow from them. Two kinetochores form on the centromeres of each dyad and the mitotic spindles attach to them, connecting each dyad’s chromatid to a spindle fibre from a pole.
What happens in Metaphase?
The chromosomes (dyads) line up along the centre line of the cell, called the metaphase plate.
What happens in Anaphase?
Spindle fibres contract, pulling the chromosomes apart & causing them to separate. They are then pulled to opposite pole ends, both taking a chromatid from each dyad.
What happens in Telophase?
A nuclear membrane forms around each cluster of chromosomes & the chromosomes relax into fine, thread-like, invisible chromatin. Cytokinesis occurs as a belt of actin protein forms around the middle of the cell, pinching it until it splits into two daughter cells.
G1 phase has a DNA damage checkpoint. What happens here?
A protein called P53 holds the cell in G1 until any DNA damage is repaired, preventing the replication of damaged DNA. If damage is unfixable, P53 can instruct apoptosis aka programmed cell death.
G2 has a DNA damage checkpoint. What happens here?
G2 monitors okazaki fragments on the lagging strand of replicated DNA. the cell will not move onto the M phase until all fragments have been incorporated into a continuous DNA strand by removal of RNA primers & closing of gaps by ligase. This ensures DNA has been replicated successfully before the next stage.
Where do spindle checkpoints take place & what happens there?
Spindle checkpoints take place in the M phase. The M phase checkpoints assess formation of spindles & holds the cell, preventing cytokinesis aka separation of the cytoplasm. Checks are made on the attachment of fibres to kinetochores & in the direction of which the fibres pull the chromosomes. Apoptosis aka programmed cell death is instructed if damage can’t be fixed.
