microtubules are formed in actin skeleton in eukaryotic cells.
microtubules are formed in actin skeleton in eukaryotic cells.
where are microtubules formed in eukaryotic cells?
actin skeleton
prior to the work of jones et al., 2001, the cell wall was believed to be the deciding factor for many bacterial cell shapes, including rods and spirals. when studied, many misshapen bacteria were found to have mutations linked to development of a cell envelope. the cytoskeleton was once thought to be a feature only of eukaryotic cells, but homologues to all the major proteins of the eukaryotic cytoskeleton have been found in prokaryotes. harold erickson notes that before 1992, only eukaryotes were believed to have cytoskeleton components. however, research in the early '90s suggested that bacteria and archaea had homologues of actin and tubulin, and that these were the basis of eukaryotic microtubules and microfilaments. although the evolutionary relationships are so distant that they are not obvious from protein sequence comparisons alone, the similarity of their three-dimensional structures and similar functions in maintaining cell shape and polarity provides strong evidence that the eukaryotic and prokaryotic cytoskeletons are truly homologous. three laboratories independently discovered that ftsz, a protein already known as a key player in bacterial cytokinesis, had the "tubulin signature sequence" present in all α-, β-, and γ-tubulins. however, some structures in the bacterial cytoskeleton may not have been identified as of yet.
cytoskeleton
we take from this that prokaryotic cells are simpler in structure, they have no nucleus, organelles, and very little of dna, in the form of a single chromosome. eukaryotic cells have nucleus with multiple organelles and more dna arranged in linear chromosomes. we also see that the size is another difference between these prokaryotic and eukaryotic cells. the average eukaryotic cell has about 25 times more dna than a prokaryotic cell does. replication occurs much faster in prokaryotic cells than in eukaryotic cells; bacteria sometimes only take 40 minutes, while animal cells can take up to 400 hours. eukaryotes also have a distinct operation for replicating the telomeres at the end of their last chromosomes. prokaryotes have circular chromosomes, causing no ends to synthesize. prokaryotes have a short replication process that occurs continuously; eukaryotic cells, on the other hand, only undertake dna replication during the s-phase of the cell cycle.
okazaki fragments