Microbial Growth and Growth Control

Question 1

Binary Fission

Answer 1

-DNA replicated, cell grows, cytoplasm evenly divided
-produces two identical daughter cells
-after replication, DNA must be segregated to opposite sides of the cell so that each daughter gets one copy
-cells elongates and a septum begins to form to separate the cell into two
-when septum formation is complete, the division site constricts and the cells are pinched off

Question 2

some things that need to be controlled during cell division

Answer 2

-needs to happen at appropriate times
-chromosome is faithfully replicated and each daughter gets one copy of genetic material
-septm forms at correct location in the cell
- nutritional status coordinated with DNA synthesis, coordinated with cell envelope synthesis, coordinated with division processes

Question 3

overview of bacterial cell cycle

Answer 3

-DNA replication is first step
-starts at oriC
-DnaA binds oriC
-DNA polymerase replicates chromosome
-two chromosomes are segregated to opposite poles
-Z ring forms - divisome
-septum forms, cells detach

Question 4

generation time

Answer 4

-can be shorter than the amount of time it takes to replicate the chromosome
-in certain, multiple DNA replication forks can be active at once
-OriC regionstarts getting replicated again before the first fork is finished
-daughter cells receive complete chromosome, and a second one whose production is in progress

Question 5

divisiome

Answer 5

-bacteria build multi-protein complexes called divisomes help identify center of the cell, build septum and seperate cells into two
-central protein is FtsZ
-divisiome helps build cell septim, including by recruiting proteins to build cell envelope that separates the newly dividing cells

Question 6

FtsZ

Answer 6

-polymerizes to form a ring arond circumference of cell at the midcell where division will occur
-constricts to help division occur

Question 7

finding the midcell

Answer 7

-nucleoid occlusion: presence of the chromosome prevents divisome from forming at that location
- another mechanism involves inhibitors of FtsZ ring formation at poles of cell

Question 8

B subtilis min system to find midcell

Answer 8

-DivIVA localized to poles, recruits MinC/MinD
-MinCD inhibit FtsZ ring formation
-MinCD concentration lowest at midterm - Z ring forms here
-nuceloud occlution factors in here as well

Question 9

cell wall growth

Answer 9

-cell wall must be remodeled but remain intact during cell division (to prevent cell from bursting)
-peptidoglycan precursors brough across cytoplasmic membrane by a lipid called bactoprenol
-autolysin: break glycolytic bonds for insertion of new monomers
-transglycosylases enzymes form new bonds in sigar backbone and & transpeptisade enzymes form new peptide corsslinks

Question 10

cell wall growth and cell shape

Answer 10

-how the new cell wall is built as cell grows larely dictates shell shape
-in most rod shaped cells, actin-like cytoskeleton protein MreB ensures new cell wall added along the long axis of cells - rod elongates
-cocci lack Mre B - spherical shape is essentially default

Question 11

budding division

Answer 11

-alternative to binary fission
-new cell grows from old by budding off from particular site on mother cell
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