Chapter 5 Lec. 1 Flashcards
cell growth and binary fission
Growth: increase in the number of cells.
Binary fission: cell division following enlargement.
Microbial growth and cell division
Increase in mass.
Increase in cell numbers
-mitosis in most eukaryotes
-budding in yeasts
Divison strategies: bacteria and archaea
Haploid only.
Asexual binary fission.
All calls must replicate and segregate genome prior to division.
Steps in binary fission
Chromosome replication. Chromosome attachment to cell membrane. Chromosome segregation. Septum formation -Inward movement of cell wall and cell membrane dividing daughter cells. Wall elongation.
Bacterial chromosomal replication
Semiconservative
-Results in one new and one parental strand.
E. coli
-Bidirectionally from single origin
-Initiates replication.
-controls frequency of initiation events.
-segregates replicated chromosomes to daughter cells.
Septation
Formation of cross walls between daughter cells.
Several steps:
-selection of site for septum formation.
-assembly of z ring.
-linkage of z ring to plasma membrane.
-assembly of cell wall synthesizing machinery.
-construction of cell and septum formation.
Fts proteins and cell division
Fts (filamentous temperature sensitive)
-essential for cell division in prokaryotes.
Found among bacteria and archaea.
Fts and cell division: FtsA, FtsZ and ZipA
Interact to form division apparatus (divisome).
FtsZ- attaches at center and forms ring.
FtsA- connects FtsZ to membrane and recruits other proteins.
ZipA- anchors FtsZ to cytoplasmic membrane.
MreB and cell morphology 1
Prokaryotes contain a cell cytoskeleton.
MreB: major shape determining factor in prokaryotes:
-forms simple cytoskeleton in bacteria and archaea.
-localizes synthesis of new peptidoglycan and other cell wall components to specific locations
Peptidoglycan synthesis and cell division
Production of new cell wall material and major feature of cell division.
- In cocci: grow in different directions.
- In rod shaped cells: occur at multiple points.
Peptidoglycan synthesis and cell division: Before cell division
Before cell division can occur, cell wall synthesis must occur.
Preexisting peptidoglycan needs to be severed to allow new peptidoglycan to form.
Peptidoglycan synthesis and cell division: Start of cell division
Beginning at FtsZ ring, small openings in wall are created by autolysins.
New cell material added across openings.
Wall band: junction between new and old peptidoglycan.
Peptidoglycan growth
- In cytoplasm uridine diphosphate attaches to NAM and NAG.
- NAM-UDP attached to NAG and bacterprenol
- Autolysins degrade peptidoglycan as new units are added.
Bactoprenol
Lipid carrier molecule that plays major role in insertion of peptidoglycan precursors
Glycolases
Enzymes that interact with bactoprenol to:
-insert cell wall precursors into growing points of cell wall.
Transpeptidation
Final step in cell wall synthesis:
-Forms the peptide cross-links between muramic acid residues in adjacent gycan chains.
Exponential growth
Most bacteria have shorter generation times than eukaryotic microbes.
Generation time dependent on growth medium and incubation conditions.
One cell splits into two (a generation) and so on- 1-2, 2-4, 4-8…
Generation time: time required for the population to double.
Exponential growth: Colony growth
Growth of colony continues until one of things occurs:
- Nutrients depleted
- water depleted
- space depletion
- waste builds and poisons cells
Exponential growth: Growth curve
Growth curve plotted by:
- Growing one species in broth at set temperature
- measuring number of bacteria at different time points.
Mathematics of exponential growth
Relationship exists between initial number of cells in culture and number after a period of exponential growth.
N=N02^n
