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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.
A telomere is a region of repetitive sequences at each end of the chromosomes of most eukaryotes. Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring chromosomes.
Resolving the question of why cancer cells have short telomeres led to the development of a two-stage model for how cancer cells subvert telomeric regulation of the cell cycle. First, the DNA damage checkpoint must be inactivated to allow cells to continue dividing even when telomeres pass the critical length threshold.
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 ...
Prokaryotic DNA Replication is the process by which a prokaryote duplicates its DNA into another copy that is passed on to daughter cells. [1] Although it is often studied in the model organism E. coli, other bacteria show many similarities. [2] Replication is bi-directional and originates at a single origin of replication (OriC). [3]
Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a one-point (the origin of replication) from which replication starts, whereas some archaea contain multiple replication origins. [26] The genes in prokaryotes are often organized in operons and do not usually contain introns, unlike eukaryotes.
Linear chromosomes are not limited to eukaryotic organisms; some prokaryotic organisms have linear chromosomes as well. Borrelia burgdorferi was the first bacterium to be found to have a linear chromosome, but new examples, such as various Streptomyces and Coxiella burnetii, have been found.
Tandem repeats have a wide variety of biological functions in the genome. For example, minisatellites are often hotspots of meiotic homologous recombination in eukaryotic organisms. [14] Recombination is when two homologous chromosomes align, break, and rejoin to swap pieces.