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Most prokaryotes, relying on circular chromosomes, accordingly do not possess telomeres. [12] A small fraction of bacterial chromosomes (such as those in Streptomyces , Agrobacterium , and Borrelia ), however, are linear and possess telomeres, which are very different from those of the eukaryotic chromosomes in structure and function.
By contrast, most eukaryotes have linear DNA requiring elaborate mechanisms to maintain the stability of the telomeres and replicate the DNA. However, a circular chromosome has the disadvantage that after replication, the two progeny circular chromosomes can remain interlinked or tangled, and they must be extricated so that each cell inherits ...
The main features of replication origins are sequences where specific initiation proteins are bound. A typical replication origin covers about 100-200 base pairs of DNA. Prokaryotes have one origin of replication per chromosome or plasmid but there are usually multiple origins in eukaryotic chromosomes.
The genomes of most eukaryotic mitochondria and plastids are in a single circular chromosome, in line with their bacterial ancestor. However, a good number of eukaryotic species do harbor linear Mitochondrial DNA (mtDNA), some even broken into multiple molecules, across a wide variety of taxa: animals (mammals, medusozoans, sponges), fungi (especially yeast), plants, and Alveolatas.
Many cancer cells are considered 'immortal' because telomerase activity allows them to live much longer than any other somatic cell, which, combined with uncontrollable cell proliferation [46] is why they can form tumors. A good example of immortal cancer cells is HeLa cells, which have been used in laboratories as a model cell line since 1951.
Other eukaryotic chromosomes, i.e., mitochondrial and plasmid-like small chromosomes, are much more variable in number, and there may be thousands of copies per cell. The 23 human chromosome territories during prometaphase in fibroblast cells. Asexually reproducing species have one set of chromosomes that are the same in all body cells. However ...
DNA diffusion. DNA within different cell types is laid out in distinct and specific 3D structures that give insight into the particular properties or traits of that cell type, said Kevin Campbell ...
The telomere-shelterin complexes that cap all eukaryotic chromosomes ensure that healthy cells can progress through the cell cycle by preventing the cellular DNA damage response from identifying chromosome ends as double-stranded breaks (DSBs). [4] [5] Without a protective cap, chromosome ends would appear identical to intrachromosomal DSBs ...