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Unformatted text preview: Exam 2 Chapter 6- Microbial Growth PART I Bacterial Cell Division 6.1 Cell Growth and Binary Fission, p. 136 Microbial growth involves an increase in the number of cells. In addition to understanding the basic science of microbial growth, there are many practical situations that call for the control of microbial growth. Fig 6.1 Growth of most microorganisms occurs by process of binary fission. When one cell divides to form two cells, one generation has occurred. Generation time- time it takes for the number of cells in a culture to double . Many bacteria have generation time of 1-3 hours. Some as little as 10 minutes, some can be days. The time required for one generation to occur depends on nutritional and genetic factors . Under ideal conditions, one generation in Escherichia coli takes 20 minutes. 6.2 Fts Proteins, the Cell Division Plane, and Cell Morphology, p. 137 Fts proteins required for cell division and chromosome replication (Fig 6.2) FtsZ proteins polymerize to form a ring FtsA protein is an ATP-hydrolyzing enzyme that provides energy for the assembly of other proteins to the ring FtsI protein is involved in peptidoglycan synthesis for the new cell wall; activity is blocked by penicillin. Divisome- division apparatus in the cell formed by Fts proteins. The FtsZ protein defines the division plan in prokaryotes and is similar to tubulin , the eukaryotic cytosketetal microtubule component. The MreB protein helps define cell shape and is similar to actin , the eukaryotic cytosketetal microfilament component MreB forms filamentous spiral shaped bands around the inside of the cell under the cytoplasmic membrane defining cell shape by directionally exerting pressure against the cytoplasmic membrane. Coccus shaped bacteria lack the MreB gene and therefore the default bacterial shape is a sphere. 6.3 Peptidoglycan Synthesis and Cell Division, p. 139 New cell wall is synthesized during bacterial growth by inserting new glycan units into preexisting wall material (Fig 6.3 & 6.4) Autolysins create small openings in existing cell wall to create space for new cell wall glycans to be integrated Autolysis (spontaneous cell lysis) may occur if there is an error in inserting new cell wall material 1 Exam 2 Bactoprenol- hydrophobic lipid alcohol that binds the N-acetylglucosamine/ N-acetylmuramic acid/pentapeptide peptidoglycan precursor and facilitates transport of these new glycan units through the cytoplasmic membrane to become part of the growing cell wall Transpeptidation- formation of peptide cross links b/t muramic acid and residues; bonds the peptidoglycan precursors into the peptidoglycan layer; this reaction is inhibited by penicillin so cell lysis occurs in presence of penicillin (FtsI is important in Transpeptidation) PART II Growth of Bacterial Populations 6.4 Growth Terminology and the Concept of Exponential Growth, p. 140 Generation time- the interval for the division of one cell to form two cells...
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