2 Reproduction and Growth Curve Flashcards
How does bacteria reproduce to form daughter cells?
Binary Fission
What are the steps of binary fission?
1) Cell elongates and DNA replicates
2) Cell wall and plasma membrane starts to split
3) Cross-wall forms, completely separating the two DNA copies
4) Cell separates
What are the different types of bacteria cultures?
Batch Culture: Growth conditions change over time
Continuous Culture: Growth conditions are kept constant (To maintain bacterias at a certain phase)
What are some characteristics of Batch Culture?
1) Number of viable cells change with time
2) The plot of viable count against time is referred to as the Growth Curve of the culture
What are the conditions required to obtain a Growth Curve in a Batch Culture?
1) Organisms are Unicellular
2) Cells used to produce the culture are derived from the Stationary phase
3) Original and new growth conditions are identical
4) Batch Culture is produced
What are the Four Basic Phases in a typical Growth Curve?
1) Lag phase
2) Log phase
3) Stationary phase
4) Death/ Decline phase
What are the characteristics of the Lag Phase?
It’s a period of intense metabolic activity with no cell division
It’s affected by:
1) Medium composition (Nutrients)
2) Temperature, pH and redox potential
3) Age (Phase harvested), condition (Injured/ Healthy) and form of cells (Vegetative Vs Spores)
4) Size of inoculum (No. of starting cells)
What are the characteristics of the Log phase?
1) Number of cells increase in an exponential fashion
2) Characteristic of cells
- Clear visible features
- Most active metabolically
- Most sensitive to adverse conditions
What is bacterial growth defined in terms of?
Doubling Time: Time taken for population to double
Mean Generation Time: Average time taken for a single cell to produce two daughter cells
What are the characteristics of the Stationary phase?
- Rate of microbial deaths = Rate of new cell production
- This is due to:
1) Accumulation of toxic products
2) Exhaustion of Nutrients
3) Changes in pH and redox potential
This causes rate of cell division to drop and rate of cell death to increase
What are the characteristics of the Stationary phase?
- Rate of microbial deaths = Rate of new cell production
- This is due to:
1) Accumulation of toxic products
2) Exhaustion of Nutrients
3) Changes in pH and redox potential
This causes rate of cell division to drop and rate of cell death to increase
What are the characteristics of the Death phase?
- Rate of cell death > Rate of new cell production
- Cell declines exponentially
- Attributed to Auto-intoxication
What are the 3 modes of sexual reproduction of bacteria?
1) Transformation
2) Conjugation
3) Transduction
What is the process of Transformation?
1) Donor cell disintegrates and liberates fragments of its DNA into the environment
2) Recipient cell takes up the DNA fragment and aligns it with complementary bases
3) Recombination occurs betw donor and recipient DNA
4) Recombinant cell is formed
What are the conditions and examples for Transformation to take place?
1) Donor and recipient must be closely related
2) Recipient is in the late log phase of growth and has to be competent
Examples:
1) Formation of capsules and pigment
2) Variation in nutrient requirements
3) Variation in virulence
What is the 2 process of Conjugation?
F- recipient cell is converted into F+ cell; no recombination:
1) F factor is replicated and transfers over to the F- cell through the Conjugal junction
F- recipient cell is converted to recombinant F- cell; recombination occurs:
1) Recombination occurs between F factor and chromosome in F+ cell
2) F factors is inserted into chromosome, forming a High Frequency of recombination (Hfr) cell
3) When connected to F- cell, replication and transfer of part of the chromosome occurs
4) Recombination occurs between Hfr chromosome fragment and F- chromosome, forming aRecombinant F- Cell
What are the conditions for Conjugation to occurs?
1) Contact betw living cells required
2) Cells should be of opposite mating types (F+ and F-)
What is the process of Transduction?
1) Phage infects donor bacteria cell
2) Phage DNA and proteins are made, and bacterial chromosome is broken into pieces
3) During phage assembly, pieces of bacterial DNA are packaged in a phage capsid. Donor cell lyses and release phage particles containing bacterial DNA
4) Phage carrying bacterial DNA infects new host cell, the recipient cell
5) Recombination occurs producing recombinant cell
What are the chracteristics of Transduction?
1) Bacterial DNA is passed via phage to recipient cell
2) Phage is host specific
3) Can be generalised or specialised
