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What is Mitosis?
Mitosis is the process where cells divide to produce new cells. If you cut your hand, new cells are produced to heal the wound. These new cells are produced through this process of mitosis. Your body is continually producing new cells to replace old ones even in the absense of an accident like cutting your hand. New cells are also produced as you are growing. The cell has a very orderly process that is used to produce these new cells which we call mitosis. Almost all organisms (all eukaryotic organisms) produce new cells in this manner. Bacteria on the other hand (prokaryotic organisms) produce new cells through a different, relatively more simple mechanism called binary fission. So, eukaryotes (like us, other mammalls and plants to name a few) produce new cells by mitosis and prokaryotes (bacteria) produce new cells through binary fission. When discussing mitosis you may also hear about meiosis. The main difference between these two are the number of chromosomes that result in the cells that are produced. Mitosis produces 2 new cells with the full set of 46 chromosomes (diploid) while meiosis produces cells with half the number of chromosomes (23 chromosomes in the haploid set for humans). The cells produced through meiosis are called gametes and are are used for reproduction. Mitosis starts with a diploid cell (46 chromosomes) and ends with 2 diploid cells.
What are the stages of mitosis?
There are 4 main stages of mitosis (prophase, metaphase, anaphase and telophase).
In prophase the chromosomes condense, the nuclear envelope breaks down, the centrioles move to opposite poles and the spindle fibers attach to the centromeres of each chromosome. The chromosomes are then pulled to the center of the cell (the metaphase plate or equatorial plane).
Metaphase is defined as the stage when the centromeres of each chromosome are aligned on the equatorial plane.
In anaphase the chromosomes are being pulled to opposite poles. The sister chromatids (copies of each chromosome) separate (disjoin) and then are each pulled to opposite poles (46 to each side).
In telophase the spindle fibers dissociate, and the nuclear envelope reforms around each new set of chromosomes. This is followed by cytokinesis where the cell divides into 2 new cells- one around each set of chromsomes within a nucleus.
Definitions to make flashcards:
anaphase - the stage of mitosis when sister chromosomes are being pulled to opposite poles by the spindle fibers
centrioles - the cellular structures which spindle fibers attach to at opposite poles of the cell
centromere - the region of the chromosome that the spindle fibers (and kinetochore) attach to
centrosome - the region where the centrioles are located
chiasma - the structures visible where homologous chromosomes have crossed over
chromatin - the term for chromosomes when they are relatively unwound and less visisble during interphase
chromosome - the large structures made of DNA and histone proteins which contain many genes that carry the hereditary information
crossing over - a process where homologous chromosomes swap portions of similar DNA through recombination
homologous chromosomes - pairs of chromosomes which exist in any diploid cell that have the same genes (but possibly different versions or alleles)
interphase - the portion of the cell cycle when the cell is not going through mitosis or meiosis
kinetochore - the protein structure that forms on top of each centromere and to which the spindle fibers connect
meiosis - the process that produces haploid reproductive cells in eukaryotes
Meiosis I - the portion of Meiosis when homologous chromosomes pair, cross over and then separate to opposite poles
metaphase - the state of mitosis when the centromeres of each chromosome have reached the center of the cell
mitosis - the process by which a eukaryotic cell replicates its DNA and divides into two identical cells
p arm - the short arm of the chromosome (the chromosome is divided in two regions by the centromere)
prophase - the first phase of mitosis where the nuclear envelope breaks down, centrioles move to opposite poles and chromosomes condense
q arm - the long arm of the chromosome (the chromosome is divided in two regions by the centromere)
S phase - the portion of interphase when the chromosomes (DNA) are being replicated
sister chromatids - the copies of each chromosome which are paired at the centromere during Meiosis and Mitosis
synaptonemal complex - a structure which forms between homologous chromosomes during Prophase I of Meiosis
telophase - the phase of mitosis when the nuclear enelope begins to form and spindle fibers break down right before cytokinesis
terminalization - when the chiasma move towards the end of the chromosomes (near the completion of Prophase I of Meiosis)
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