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MICB 201 (35)
Chapter 04-1


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MICB 201
Wade Bingle

Chapter 6 • Describe the role of FtsZ in cell division. FtsZ is a protein that is involved in the cell division of MOST prokaryotes. It is a protein that acts as a subunit and it assembles as a ring when the dividing cell is expanding and its genetic material is copied. The ring is assembled between the duplicated nucleoids – the nucleoids are on opposite poles and they are basically identical. Anchored to the inner surface of the CM, the FtsZ ring contracts by shedding subunits into the cytoplasm; pulling the membrane inward eventually pinching them off. So basically FtsZ is assembled while/after the genetic material has been copied and starts contracting when the nucleoids are in the emerging cells. • Describe the different ways the synthesis of rigid cell wall polysaccharides is coordinated with FtsZ ring constriction. For organisms without a rigid cell wall, they just pinch off their membrane – easy. For organisms with a rigid cell wall, the situation is more variable for cell division. The FtsZ ring not only pinches off the membranes but it serves also as a scaffold for the synthesis of new cell wall material at the division site. In some prokaryotes, the joint b/t the new cell wall material is degraded at the same time the membrane is constricted by FtsZ. Then the cells just pinch off. In the other prokaryotes, a cross wall (septum) is completed in the final stages of FtsZ constriction. Later, enzymes digest part of the cross wall/septum. • Explain the difference between FtsZ-based symmetric cell division, asymmetric cell division, budding and bipolar cell division with respect FtsZ ring localization, synthesis of new cell wall relative to the FtsZ ring and the nature of the daughter cells relative to the parental cell. Symmetric cell division is the most common in prokaryotes, exhibited by cocci, rods, spirilla, etc. In a cell, there is a FtsZ ring in the middle with new wall material synthesized on either side equally. The daughter cells are identical. This means each cell is half new, half old. So symmetric cell division = binary fission. In non-spherical cells, symmetric cell division first involves the synthesis of new cell wall material at other sites in addition to the division site. Another method is fragmentation done by Bdellovibrio. Fragmentation is simply a variation on symmetric cell division but instead of 2 daughter cells there are lots more. A long chain or filament of incompletely separated cells is initially formed. The filament then undergoes FtsZ dependent cell division resulting in simultaneous formation of unicells. Bdellovibrio reproduces in the periplasm of other cells. Incomplete cell division – In some prokaryotes, a significant fraction of cells never completely separate after symmetric cell division. Therefore, chains/filaments or clumps of cells result depending on the orientations of the division planes. If they only divide on one plane you get a chain. If they divide on 3 planes then you get a clump. Asymmetric cell division – Caulobacter has a stalk that sticks to surfaces (adhesive polysaccharide glue) and
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