Bacterial Growth and Cell Division Flashcards
What is the function of Recombinant E.coli
Used to express proteins for medical or commercial purposes e.g. insulin
Why is recombinant E.coli useful in the lab
Fast growth rate allows lots of protein to be made rapidly
What are the 4 stages of bacterial growth
Lag, exponential, stationary and death phases
Define growth
An increase in the number of cells
Define generation time
The time needed for one cell to divide and form 2 cells
How can bacterial culture growth be described
Exponential growth
What is exponential growth in terms of bacterial culture growth
The number of cells doubles at constant time intervals as cells multiply until eventually limited by nutrients or accumulated toxins
What occurs in the lag phase
Cells adjust to new conditions and synthesise required metabolic enzymes and metabolites
What occurs in the exponential phase
Optimal growth with regular doubling in cell numbers
What occurs in the stationary phase
Growth is limited by nutrient depletion or accumulation of toxic metabolites. Rate of new cell production is balanced with rate of cell death so no overall growth in culture
What occurs in the death phase
Complex gradual loss of viability but with some cell turnover
How do most bacteria grow at the cellular level (what process)
Binary fission
What is binary fission
Cell elongates to twice its length and then splits down the middle
What are the 4 main steps of binary fission
1) cell grows and duplicates structures, chromosomes are replicated
2) daughter chromosomes segregate to different ends of the cell
3) septum forms at mid cell and new poles are synthesised as the z-ring constricts
4) cell division occurs mid-cell resulting in 2 identical daughter cells
What is a replisome
DNA replication machinery
What is the replication fork
The structure formed as DNA is replicated
What shape are bacterial chromosomes
Generally circular
How are chromosomes replicated in bacteria
Bidirectional replication from a single fixed origin (oriC) to the terminus (terC)
How can bacteria divide more frequently than the time taken for complete chromosome replication
They initiate replication in the previous cell cycle by replisomes binding to both new and old DNA during replication
Describe the 4 steps of bacterial chromosome replication
1) Replisomes bind to oriC
2) bidirectional replication of DNA
3) as DNA is replicated more replisomes binding to both new and old DNA
4) Initial replication complete, chromosomes segregate and cells divide, each cell with one copy of the chromosome
Describe how chromosome replication is ‘highly choreographed’ to ensure each cell gets a copy of the chromosome (3 main methods)
- oriC is localised to the middle of the cell
- left and right arms of the circular chromosome are carefully positioned
- during chromosome replication daughter oriCs are localised to a quarter distance along the cell (one at 1/4 and another at 3/4 along)
What is the divisome/ Z-ring
The cell division machinery which is a complex contractile ring
Which protein is the key player in the assembling of the Z-ring
FtsZ protein
What governs septum formation and cell pole synthesis (and therefore ultimately division) in bacterial cell division
The Z-ring/ divisome
