22 Dec 2011

Cell Division

1. What is mitosis? What is the importance of mitosis?
Mitosis is the process in which one eukaryotic cell divides into two cells identical to the parent cell generally identical, since alterations in genetic material can occur, more or less organelles may be distributed between the daughter cells, etc.Mitosis is fundamental for asexual reproduction of eukaryotes, for the embryonic development, for the growth of pluricellular beings and for tissue renewal.
2. What is cell cycle? 
Cell cycle, or mitotic cycle, is the time period that begins when the cell is created and finishes when it is divided by mitosis creating two daughter cells. The cell cycle is divided into interphase and the mitotic phase.
3.What are the main events of the first mitotic period?
The first mitotic period is prophase. During prophase the following events occur: migration of each centriole pair centrioles were duplicated in interphase to opposite cell poles; aster formation around the centriole pairs; formation of the spindle fibers between the two centriole pairs; end of chromosome condensation; disintegration of the nucleolus; breaking of the karyotheca; dispersion of condensed chromosomes in the cytoplasm; binding of chromosomes to the spindle fibers.
4.What is the name of the cytoplasm division in the end of mitosis? What are the differences in this process between animal and plant cells?
Cytoplasm division occurs after telophase and it is called cytokinesis. In animal cells an invagination of the plasma membrane toward the cell center appears in the equator of the parent cell and then the cell is strangulated in that region and divided into two daughter cells. This type of division is called centripetal cytokinesis from outside.In plant cells the cytokinesis is not centripetal since the division happens from the inside. Membranous sacs full of pectin concentrate in the internal central region of the cell and propagate to the periphery toward the plasma membrane. The pectin-containing sacs fuse themselves and form a central structure called phragmoplast. On the phragmoplast cellulose deposition occurs and a true cell wall is created to separate the daughter cells. Plant cells thus present centrifugal cytokinesis.

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