![]() In this example, FtsZ is the ancestor protein to tubulin (a modern protein). ![]() ![]() In addition, both FtsZ and tubulin employ the same energy source, GTP (guanosine triphosphate), to rapidly assemble and disassemble complex structures.įtsZ and tubulin are homologous structures derived from common evolutionary origins. FtsZ proteins can form filaments, rings, and other three-dimensional structures that resemble the way tubulin forms microtubules, centrioles, and various cytoskeletal components. However, the FtsZ protein that plays such a vital role in prokaryotic cytokinesis is structurally and functionally very similar to tubulin, the building block of the microtubules that make up the mitotic spindle fibers that are necessary for eukaryotes. Prokaryotic cells, on the other hand, do not undergo karyokinesis and therefore have no need for a mitotic spindle. Mitotic Spindle ApparatusThe precise timing and formation of the mitotic spindle is critical to the success of eukaryotic cell division. (credit: modification of work by “Mcstrother”/Wikimedia Commons) Evolution Connection These images show the steps of binary fission in prokaryotes. When the new cell walls are in place, the daughter cells separate. A septum is formed between the nucleoids, extending gradually from the periphery toward the center of the cell. Formation of the FtsZ ring triggers the accumulation of other proteins that work together to recruit new membrane and cell wall materials to the site. The formation of a ring composed of repeating units of a protein called FtsZ directs the partition between the nucleoids. After the chromosomes have cleared the midpoint of the elongated cell, cytoplasmic separation begins. As the cell elongates, the growing membrane aids in the transport of the chromosomes. As the new double strands are formed, each origin point moves away from the cell wall attachment toward the opposite ends of the cell. Replication of the DNA is bidirectional, moving away from the origin on both strands of the loop simultaneously. ![]() The starting point of replication, the origin, is close to the binding site of the chromosome to the plasma membrane ( Figure). The bacterial chromosome is attached to the plasma membrane at about the midpoint of the cell. The packing proteins of bacteria are, however, related to the cohesin and condensin proteins involved in the chromosome compaction of eukaryotes. Although the DNA of the nucleoid is associated with proteins that aid in packaging the molecule into a compact size, there are no histone proteins and thus no nucleosomes in prokaryotes. The single, circular DNA chromosome of bacteria is not enclosed in a nucleus, but instead occupies a specific location, the nucleoid, within the cell (). Due to the relative simplicity of the prokaryotes, the cell division process, called binary fission, is a less complicated and much more rapid process than cell division in eukaryotes. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |