6.2 Mitosis Flashcards
Mitosis
Cell division in eukaryotic cells that produces 2 genetically identical daughter cells
When is mitosis necessary?
During growth, replacement and repair of tissues in multicellular organisms
Necessary for asexual reproduction - cloning
How do prokaryotic organisms reproduce?
By binary fission
Chromatids
2 identical copies of DNA (chromosome) - held together at a centromere
Chromatin
Uncondensed DNA in a complex with histones
Why is important that chromatids are kept together during mitosis?
So that they can be precisely manoeuvred and separated equally, one for each new daughter cell
4 stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
How can mitosis be viewed?
Growing root tips of plants
Treated with chemical to allow cells to be separated
Squashed to form one layer of cells on the slide
What happens during prophase?
Chromatin fibres coil and condense to form chromosomes
Nucleolus disappears
Nuclear membrane begins to break down
Protein microtubules form spindle fibre structures linking the poles of the cell
Fibres forming the spindle are necessary to move chromosomes into the correct position before division
Two centrioles migrate to opposite poles of the cell
Spindle fibres attach to specific areas of the centromere and start to move the chromosomes to the centre of the cell
What happens during metaphase?
Chromosomes are moved by spindle fibres to form a plane in the centre of the cell - metaphase plate
Held in position
What happens during anaphase?
Centromeres holding chromatids together divide during anaphase
Chromatids separate and pulled to opposite ends of the cell by shortening spindle fibres
What happens during telophase?
Chromatids have reached the poles and are now called chromosomes
Two new sets of chromosomes assemble at each pole and nuclear envelope reforms around them
Chromosomes start to uncoil and nucleolus is formed
After this, cytokinesis begins
Cytokinesis in animal cells
Cleavage furrow forms around the middle of the cell
Cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle, forming two cells
Why can plant cells not have a cleavage furrow?
They have cell walls
Cytokinesis in plant cells
Vesicles from Golgi apparatus begin to assemble in the same place as where metaphase plate was formed
Vesicles fuse with each other and cell surface membrane - dividing cell into two
New sections of cell wall then form along the new sections of membrane
