Mitosis 6.2 Flashcards
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what is the misunderstanding around mitosis
Mitosis is the term usually used to describe the entire process of cell division in eukaryotic cells. It actually refers to nuclear division (division of the nucleus)
apart from Cell division in eukaryotic cells what is mitosis necessary for
Asexual reproduction, which is the production of genetically identical offspring from 1 parent in multicellular organisms including plants, fungi and some animals and also in eukaryotic single-celled organisms such as Ameoba species
Prokaryotic organisms, including bacteria do not have a nucleus and they reproduce asexually by a different process known as binary fission
what is a chromosome
A molecule of DNA
what is a chromatid and when is it formed
Before mitosis can occur, all of the DNA in the nucleus is replicated is replicated during interphase. Each DNA molecule (chromosome) is converted into 2 identical DNA molecules, called Chromatids
What is a centromere and what is its function
- region where 2 sister chromatids join together
- necessary to keep chromatids together during cell division
^ for precise manoeuvrability and segregation
what are the stages of mitosis
There are 4 stages of mitosis - prophase, metaphase, anaphase and telophase
we describe them separately but in fact they flow seamlessly from one to another
what cells can be used to observe the stages of mitosis
dividing cells can be easily obtained from growing root tips of plants. The root tips can be treated with a chemical to allow the cells to be separated - then they can be squashed to form a single layer of cells on a microscope slide. Stains that bind DNA are used to make chromosomes clearly visible
what occurs in prophase
1)During prophase, chromatin fibres (complex made up of various proteins, RNA and DNA) begin to coil and condense to form chromosomes that will take up stain to become visible under the light microscope. The nucleolus, a distinct area of the nucleus responsible for RNA synthesis, disappears. The nuclear membrane begins to break down
2)Protein microtubules form spindle-shaped structures linking the poles of the cell. The fibres forming the spindle are necessary to move the chromosomes into the correct positions before division
3)In animal cells and some plant cells, 2 centrioles migrate to opposite poles of the cell. The centrioles are cylindrical bundles of proteins that help in the formation of the spindle
4)The spindle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell
5)By the end of prophase the nuclear envelope has disappeared
what occurs in metaphase
During metaphase the chromosomes are moved by the spindle fibres to form a plane in the centre of the cell called the metaphase plate, and then held in position
what occurs in anaphase
The centromeres holding together the pairs of chromatids in each chromosome divide during anaphase. The chromatids are separated - pulled to opposite poles of the cell by the shortening spindle fibres
The characteristic ‘V’ shape of the chromatids moving towards the poles is a result of them being dragged by their centromeres through the liquid cytosol
What occurs in telophase
In telophase the chromatids have reached the poles and are now called chromosomes. The 2 new sets of chromosomes assemble at each pole and the nuclear envelope reforms around them.
The chromosomes start to uncoil and the nucleolus is formed.
Cell division or cytokinesis, begins
what is cytokinesis
- the division of the cell into 2 or 4 separate cells (depending on meiosis or mitosis),
- begins during telophase
how does cytokinesis occur in animal cells
- cleavage furrow forms at middle of cell
- membrane pulled inwards by the cytoskeleton until close enough to fuse
- forms 2 cells
How does cytokinesis occur in plant cells
Vesicles from the golgi apparatus begin to assemble in the same place as where the metaphase plate was formed. The vesicles fuse with each other and the cell surface membrane, dividing the cell into 2
New sections of cell wall then form along the new sections of membrane (if the dividing cell wall were formed before the daughter cells separated they would immediately undergo osmotic lysis from the surrounding water)
