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Bacterial Cell Division 5.1Cell Growth and Binary Fission 5.2Fts Proteins and Cell Division 5.3MreB and Determinants of Cell Morphology 5.4Peptidoglycan Synthesis and Cell Division © 2012 Pearson Education, Inc. 5.1 Cell Growth and Binary Fission Growth: increase in the number of cells Binary fission: cell division following enlargement of a cell to twice its minimum size (Figure 5.1) Generation time: time required for microbial cells to double in number During cell division, each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell © 2012 Pearson Education, Inc. Animation: Binary Fission Animation: Binary Fission Animation: Overview of Bacterial Growth Animation: Overview of Bacterial Growth Figure 5.1 Septum Cell elongation Septum formation Completion of septum; formation of walls; cell separation One generation © 2012 Pearson Education, Inc. 5.2 Fts Proteins and Cell Division Fts (filamentous temperature-sensitive) Proteins (Figure 5.2) –Essential for cell division in all prokaryotes –Interact to form the divisome (cell division apparatus) FtsZ: forms ring around center of cell; related to tubulin ZipA: anchor that connects FtsZ ring to cytoplasmic membrane FtsA: helps connect FtsZ ring to membrane and also recruits other divisome proteins –Related to actin © 2012 Pearson Education, Inc. Figure 5.2 Cytoplasmic membrane Outer membrane Cytoplasmic membrane Divisome complex Peptidoglycan FtsZ ring © 2012 Pearson Education, Inc.

5.2 Fts Proteins and Cell Division DNA replicates before the FtsZ ring forms (Figure 5.3) Location of FtsZ ring is facilitated by Min proteins –MinC, MinD, MinE FtsK protein mediates separation of chromosomes to daughter cells © 2012 Pearson Education, Inc. Figure 5.3 Cell wall Min CD Cytoplasmic membrane Nucleoid MinE Divisome complex FtsZ ring Nucleoid Septum MinE Minutes 0 20 40 60 80 © 2012 Pearson Education, Inc.

5.3 MreB and Determinants of Cell Morphology Prokaryotes contain a cell cytoskeleton that is dynamic and multifaceted MreB: major shape-determining factor in prokaryotes –Forms simple cytoskeleton in Bacteria and probably Archaea –Forms spiral-shaped bands around the inside of the cell, underneath the cytoplasmic membrane (Figure 5.4a and b) –Not found in coccus-shaped bacteria © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology MreB (cont’d) –Localizes synthesis of new peptidoglycan and other cell wall components to specific locations along the cylinder of a rod-shaped cell during growth © 2012 Pearson Education, Inc. Figure 5.4a Cell wall Cytoplasmic membrane MreB Sites of cell wall synthesis FtsZ © 2012 Pearson Education, Inc. Figure 5.4b © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology Crescentin: shape-determining protein produced by vibrio-shaped cells of Caulobacter crescentus –Crescentin protein organizes into filaments ~10 nm wide that localize on the concave face of the curved cells (Figure 5.4c) © 2012 Pearson Education, Inc.

Figure 5.4c © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology Most archaeal genomes contain FtsZ and MreB-like proteins, thus cell morphology is similar to that seen in Bacteria © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Production of new cell wall material is a major feature of cell division –In cocci, cell walls grow in opposite directions outward from the FtsZ ring –In rod-shaped cells, growth occurs at several points along length of the cell © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Preexisting peptidoglycan needs to be severed to allow newly synthesized peptidoglycan to form –Beginning at the FtsZ ring, small openings in the wall are created by autolysins –New cell wall material is added across the openings –Wall band: junction between new and old peptidoglycan © 2012 Pearson Education, Inc.

Figure Big Bang Theory Season 6 Episode 1 Download Avi. 5.5 FtsZ ring Wall bands Growth zone Septum © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Bactoprenol: carrier molecule that plays major role in insertion of peptidoglycan precursors –C 55 alcohol (Figure 5.6) –Bonds to N-acetylglucosamine/ N-acetylmuramic acid/pentapeptide peptidoglycan precursor © 2012 Pearson Education, Inc. Figure 5.6 Hydrophobic portion © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Glycolases: enzymes that interact with bactoprenol (Figure 5.7a) –Insert cell wall precursors into growing points of cell wall –Catalyze glycosidic bond formation © 2012 Pearson Education, Inc. Figure 5.7a Transglycosylase activity Growing point of cell wall Cytoplasmic membrane Autolysin activity Pentapeptide Bactoprenol Peptidoglycan Out In © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Transpeptidation: final step in cell wall synthesis (Figure 5.7b) –Forms the peptide cross-links between muramic acid residues in adjacent glycan chains –Inhibited by the antibiotic penicillin © 2012 Pearson Education, Inc.