Cell division embryonic development

Figure 11.4-3. Telomeres and telomerase. Telomere is a repeating sequence of double-stranded DNA located at the ends of chromosomes. Long telomere length is associated with immortalized cell lines, cancer cells, and embryonic stem cells. Cells experience telomere shortening with each cell division. Telomerase is an enzyme that lengthens telomeres by adding on repeating sequences of DNA. Telomerase binds the ends of the telomere via an RNA template that is used for the attachment of a new strand of DNA. Telomerase adds several repeated DNA sequences, then releases to a second enzyme, DNA polymerase, and attaches the opposite or complementary strand of DNA, completing the double-stranded extension of the chromosome ends. The function of telomere and telomerase seem to be important in cell division, normal development, and cancer research. (This figure is available in full color at ftp //ftp.wiley.com/public/sci tech med/pharmaceutical biotech/.)...

Asymmetric cell division is a universal mechanism utilized for the generation of cellular diversity during development (for reviews see Horvitz Herskowitz 1992, Guo Kemphues 1996, Shapiro Losick 1997, Jan Jan 1998). Asymmetric cell divisions during Drosophila embryonic development involve both extrinsic cues mediated through Notch and Delta and intrinsic cell fate determinants and play a major role in producing the distinct cell types which are... 

Stem cells are present in the earliest stage of embryonic development the blastocyst. Embryonic stem cells are pluripotent, meaning they are capable of generating any terminally differentiated cell in the human body that is derived from any one of the three embryonic germ layers ectoderm, mesoderm, or endoderm [8]. All the body s organs arise through a series of divisions and differentiations from the original embryonic stem cells that form the blastocyst [3]. 

Prior to cell division, the nucleus replicates itself so that the two new cells will each contain genetic information. Several nuclear enzymes coordinate the replication of DNA. During cell division, the nuclear envelope breaks down, and equal copies of DNA and cytoplasm are partitioned into two daughter cells. After division, the nuclear envelopes reform in each daughter cell around its own copy of DNA. This fundamental sequence of events allows for the continuation of eukaryotic life during embryonic development and cellular regeneration throughout life. 

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