module 3 Flashcards
phases of the bacterial cell cycle
Growth Phase:
After cell birth, it grows
Chromosomes are replicated and separated
Septum and daughter cells are formed.
Binary Fission
A simple type of cell division where the cell divides into two equivalent daughter cells.
Nucleoid Replication
The nucleoid replicates and divides, with one chromosome moving to each half of the cell.
Chromosomes are properly segregated into each daughter cell, involving ParA, ParB, and ParS proteins.
Septum Formation
The cell envelope contracts and forms a septum (cross wall) at the midcell, separating the cytoplasmic contents into two new cells.
MinD and MinE Proteins: Localize MinC and ensure that the Z ring is formed at the midcell.
FtsZ Protein: Forms the Z ring (future division site of the cell).
MinC Protein: Inhibits FtsZ polymerization at the poles.
Site of Septum Formation:
Cocci and Rods
The mechanism for choosing the site of septum formation involves the FtsZ, MinC, MinD, and MinE proteins to ensure proper midcell formation and division.
Alternative Methods for Bacterial Cell Division:
Budding:
Some bacteria produce progeny by budding off a larger parent cell.
Archaeal Cell Cycles
Resemble eukaryotic cell cycles
DNA replication.
Preparation for division.
Separation of chromosomes.
Phases of a Microbial Growth Curve:
Lag Phase:
Period of adaptation where bacteria prepare for growth.
Initial phase after cells are added to a fresh medium.
Cells are not dividing but actively adapting gene expression.
Log Phase (Exponential Phase):
Period of rapid, exponential growth (maximum rate supported by available nutrients).
Appears as a straight line on the log scale.
Continues until nutrients become limited and waste accumulates.
Stationary Phase:
Growth rate slows as nutrients are depleted and waste accumulates.
Shoulder Phase: Gradual slowing of growth as nutrients deplete and waste accumulates.
Growth rate equals the death rate; cell numbers stabilize.
Cells adapt to the new environment by changing gene expression.
Death Phase:
Decline in the number of viable bacteria due to the harsh environment.
Long-Term Stationary Phase:
Extended phase with no net change in viable cell numbers.
Some cells adapt by scavenging energy from dead cells, leading to the emergence of variants over time.
Factors Influencing Microbial Growth and Adaptation:
Water Availability/Solute Concentration
pH
Temperature
Temperature Categories
Oxygen Concentration
Pressure
Radiation
Hypotonic Vs Hpertonic Environments
Hypotonic: Lower concentrations outside the cell; water flows into the cell by osmosis
Hypertonic Higher concentrations outside the cell; water flows out of the cell by osmosis.
Halophiles
Live in high salt concentrations.
Halotolerant
Can grow in salt solutions but do not require high concerntrations of salt for growth
Acidophiles
Optimum growth between pH 0 and 5.5
Neutrophiles
Optimum growth between 5.5 and 8.0
Temperature for Microbial growth
rely on external temperatures.
adapted for environmental temperatures.
