MGY377 Lecture 11 Review

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Department
Molecular Genetics and Microbiology
Course
MGY377H1
Professor
John Brumell
Semester
Fall

Description
MGY377 Lecture 11 – Bacterial Cell Cycle and Growth - Bacterial growth o An increase in the number if cells o Every cell has a lifespan  Species must replenish itself by growth o Important to understand microbial growth  Food  Biotechnology  Fighting disease o During growth cycle, all cellular constituents increase in number o Partitioning of replicated DNA (chromosomes) depends on its association with membranes o Time required for growth cycle varies greatly  Different species  Nutritional species  Stress and environment  E. coli replicates every 20 minutes in rich medium; E. coli replicates every 24 hours in the gut - Binary fission o Cell divides into two cells  Elongate to approximately twice the length of the smallest cell  Form a partition called a septum  As a result of inward growth of cytoplasmic membrane and cell wall  Two daughter cells are pinched off o Mechanism  DNA replication  Cell elongation  Septum formation  Completion of septum with formation of distinct walls  Cell separation - Bacterial cell division o Many proteins involved in cell division o Fts = filamentous temperature sensitive  Describes mutants lacking these genes  These proteins interact to form a division apparatus called the divisome  FtsZ, FtsA, FtsW, FtsI, FtsQ, FtsK... o FtsZ  GTPase recruits divisiome that creates a FtsZ polymer ring  Highly conserved and distributed among prokaryotes  Structural homology to tubulin found in eukaryotic cells  Forms a membrane-associated ring structure at the bacterial midcell during division (FtsZ-ring)  FtsZ breaks down and is diffuse in the cytosol o ZipA  anchor FtsZ to the cytoplasmic membrane o FtsA  ATPase provides energy for divisome assembly o FtsI  involved in PG transpeptidation o FtsK  assists with chromosome separation - Paradigm shift o Daughter cells are not created equal o Tracked growth characteristics of individual cells and all their progeny using video microscopy o The concept of inequality  During cell division, each daughter cell gets one new cell pole and one old cell pole  Subsequent division gives daughter cells that can arise either from the new pole or the old pole  Vertical length of lines is proportional to growth rate of the cell  Old pole progeny cells grow 2.2% slower than new pole progeny cells  Old pole cells divde less frequently, thus less offspring biomass  The older the old pole cell, the slower the growth rate, then bacterial aging is occurring - Control of cell shape Protein Homologue Intracellular Cell shape Example structure FtsZ Tubulin Ring Sphere S. aureus MreB Actin Helical Rod E. coli B. subtilis Crescentin Intermediate Rod Crescent C. crescentus filament - Dividing in the middle o Determined by proteins of min family o MinC  Inhibits FtsZ ring formation o MinD  ATPase (ATP  ADP)  Binds to the inner cell membrane  Recruits MinC to the inner cell membrane o MinE  Stimulates removal of MinC/D from the membrane by stimulating ATP hydrolysis of MinD o Min proteins are dynamic  Localization of MinC and MinD is not static  MinC and MinD oscillates from one pole to another  MinD recruits MinC, therefore the oscillation of MinD causes MinC movement - PG synthesis and growth o New cell wall biosynthesis must take place for growth o Must be added to existing cell wall o At the beginning of FtsZ ring, small openings in cell wall are created by autolysins  Present in divisome protein complex o New cell wall material is added to fill in these areas  Junctions of new and old cell wall leaves a scar called wall bands o Controlled cutting of existing PG is simultaneous with insertion of new PG o Carrier molecule, Bactoprenol, plays a major role  C55 alcohol  Very hydrophobic  Binds to PG precursors in the cytoplasm  Transports PG precursors across the cytoplasmic membrane  New PG precursors interacts with enzymes that insert them into growing cell wall - Transpeptidation o Final step in cell wall synthesis o Involves formation of peptide cross-links between NAM residues in adjacent glycan chains  3 (mDAP or L-Lys), 4 (D-Ala) linkage  Gram(-) is typically between mDAP and D-Ala  Gram(+) is typically L-Lys and D-Ala using a glycine interbridge o Inhibited by penicillin o Regulated by FtsI - Population growth o Growth rate = change in # or mass per unit time o Generation = interval for formation of two cells o Generation time = time for one generation  Also known as doubling time  Can vary widely, depending on species and conditions - Exponential growth o Occurs when bacteria keep doubling under no restrictions o Bacteria numbers are plotted on log or semi-log plots o Calculating bacterial numbers during exponential growth  Relationship between number of cells initially present and the number of cells present after period of exponential growth o Growth rate constant  Measures the number of generations per unit time - The growth cycle o Bacteria are not always in exponential phase o Four phases of growth in batch culture (e.g., an enclosed flask)  Lag phase  Bacteria are first introduced into an environment or media  Bacteria are sensing their surroundings o Need to alter gene expression for rapid growth or to accommodate new nutrient sources  Lag occurs if cells need to undergo repair due to damage sustained in previous environment  Length of lag phase is dependent on conditions o Short lag  complex media to complex media
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