Chapter 9 Flashcards
What does bacterial growth refers to?
Bacterial growth refers to the bacterial population growth
How do prokaryotes reproduce?
ALWAYS asexual reproduction! Through Binary Fission, but some exceptions.
Where does replication start?
Starts at the origin of replication on circular chromosomes
How does the cell cytoplasm divide?
Divides in the process of cytokinesis
What protein directs cytokinesis and cell division?
FtsZ : assembles into a Z ring on the cytoplasmic membrane
What is the Divisome?
Activates to produce peptidoglycan cell wall and build a septum that divides the two daughter cells.
What is the difference between generation/doubling time in Eukaryotes and Prokaryotes?
Eukaryotes: The time between the same points of the life cycle in two successive generations.
Prokaryotes: The time it takes for the population to double through one round of binary fission.
Nt = N0 x 2^n
log10(Nt) = log10(N0 x 2^n)
n = (log10(Nt) - log10(N0)) / (log10(2))
k = n/t
g = (1/k) = (t/n)
KNOW THESE EQUATIONS!!!
This is only working if we assume the generation time is not changing and remains the same indefinitely, HOWEVER likely not the case
What does k stand for?
What does g stand for?
What does n stand for>
k = The number of generations per unit of time
g = generation time
n= the number of generations
What is the growth curve? What are the phases of the growth curve?
Growth curve: a graph modeling the number of cells in the culture over time. Distinct phases
- x = Logarithm of living bacterial cells
- y = Time
Lag phase, Log phase, Stationary phase, Death/Decline phase
What is Culture Density?
Culture density: defined as the number of cells per unit volume
Explain the Lag Phase
Lag phase: no increase in number of living bacterial cells.
Duration depending on :
- the species and genetic make-up of the cells.
- the composition of the medium
- the size of the original incolum
Inoculum: a small number if cells that is represented in the beginning of the growth curve.
- added to fresh culture medium, cells gearing for the next growth phase. Observed cells don’t change.
Explain the Log Phase
Log phase: Exponential increase in number of living bacterial cells. Cells are actively dividing by binary fission and their number increases exponentially (not linear). Shows constant growth rate, uniform metabolic activity
** growth rate is genetically determined generaation time under specific conditions for a specific bacterial strain. **
Explain Stationary Phase
Stationary phase: slows/stalls pop. growth due to unfavorable conditions (waste products accumulate, nutrients get used up, O2 decrease & limit aerobic cell growth). Live cells reaches plateau but still active.
New Cells = Cells death
Total pop. of living cells & Cell density = constant
Cells -> survival mode of metabolism. Slow synthesis of peptidoglycan, proteins, and nucleic acids.
** Sporulation or Secondary metabolic production (antibiotics) eventually happens***
Explain Death phase
Death Phase: accumulation of toxic waste and nutrients are exhausted, cell die in greater and greater numbers.
Exponential decrease in the number of cells
What is a chemostat?
Chemostat: used to maintain a continuous culture where nutrients are supplied at a steady rate to maintain cells in log phase (cell develop > cell death)
an opening to add nutrients (feed) and an outlet to remove contents (effluent)
What is bacterial counts? Bacterial Load?
Bacterial counts: consist in estimating the number of bacterial cells in a sample
Bacterial Load: The number of bacteria in a clinical sample
Direct methods v.s Indirect methods
-Direct methods: Involve counting cells
- Indirect methods: Depend of the measurement of cell presence or activity without counting individual cells.
Primary v.s. Secondary Stain
Primary Stain: (green fluorescence) penetrate cytoplasmic membranes, staining both live and dead cells
Secondary Stain: (red fluorescence) stains cells only if the cytoplasmic membrane is damaged
Viable/simply plate count
a count of viable or live cells, based on the principle that viable cells replicate and give rise to visible colonies when incubated under suitable conditions for the specimen.
What does the pH indicator do?
pH indicator that changes color from red to yellow when the lactose is fermented.
What is turbidity and what measures it?
Turbidity: cloudiness
** measures turbidity of a sample bacteria in a liquid suspension**
Spectrophotometer measures turbidity
What happens when the number of bacteria in a suspension increase
As the number of bacteria in a suspension increase, the turbidity also increases and causes less light to reach the detector.
Calibration curve
Calibration curve is generated by plitting turbidity v.s. cell density
Calibration curve can be used to estimate cell counts for all samples obtained or cultured under similar conditions and with densities within teh range of values used to construct the curve
