суббота, 2 октября 2010 г.

Cell Division (Mitosis)

Duplication (replication) of DNA and the transmission of genetic information to the two daughter cells connected with it precede every cell division and take place during the so-called interphase. The interphase is the stage between mitoses and is the working phase of the cell. Chromosomes with two chromatids are formed by duplication of the genetic material during interphase. This establishes the precondition for mitotic cell division. Chromosomes demonstrate evidence of their duplication by a longitudinal split visible in the microscopic image. The chromosomes become shorter and thicker through increased coiling. After cell division is complete, the chromosomes uncoil and, during the ensuing interphase, replicate again.
Mitotic cell divisions permit a fertilized ovum to develop into an organism. They are the preconditions for physiological renewal of cells and lead to regeneration of tissues after injury. With the exception of a fewcells (nerve cells, and cardiac and skeletal muscle cells), the ability to divide is maintained throughout the life cycle, though it varies among cells. As a rule, mitoses are less common in highly differentiated tissues.
Double helix of DNA and its duplication (replication). The double strand of DNA splits like a zipper and forms two new, completely identical DNA molecules. The original strands are shown in blue, the new ones in pink (the sugar−acid phosphate chain is shown as a band; A = adenine, C = cytosine, G = guanine, T = thymine; free nucleotide groups are marked by arrows) (After Hadorn and Wehner)

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