Plasmids and their Maintenance Flashcards
What is the difference between the core and accessory genomes in bacteria?
The core genome is the basic genetic information that is required for the cell to survive and replicate, the accessory genome is any non-essential genes that may provide some ease in survival in some way.
What is the role of the accessory genome in bacterial evolution?
The accessory genome is basically what selection acts upon, providing several different genes that may provide some benefit or hindrance in the cell’s survival. It is also the accessory genome that horizontal gene transfer usually acts upon.
What is partitioning?
There are two types of plasmids, low copy and high copy. Low copy are quite large and require a lot more machinery and therefore take up more energy. As a result they must stay in low numbers. High-copy plasmids are small and consequently do not take up a lot of energy so will exist in large numbers in the cell.
Partitioning is a process by which plasmids separate themselves into the newly formed daughter cells.
In low-copy cells specialized molecular machinery is required, whereby ParM and ParR proteins push the plasmids to opposite poles of the cell.
In high copy plasmids, as they can exist in large numbers, can undergo random partitioning.
What is conjugation for spread?
Whereby a plasmid hijacks the conjugation machinery of a cell for its own use.
What is replication/ copy number control?
In ColE1 - Plasmid replication is controlled by an inhibitor coded within the plasmid near the oriV site, Rop protein. As cell size increases inhibitor concentration decreases and plasmid replication is promoted. When concentrations of the inhibitor are high, it will associate with RNA I which binds to RNA II and prevents replication.
In F plasmid - at low concentrations RepA binds to oriC and initiates replication, at high concentrations Rep A will also bind to iteron sequences, creating handcuffs between two plasmids, preventing replication until separation at cell division.
What is multimer resolution?
Plasmid multimers often form due to random homologous recombination of replicated plasmids. Is resolved vis plasmid encoded site-specific recombination systems.
In F - this is the enzyme recombinase
In ColE1 - hijacks a similar system contained in E.coli genome as it suffers the same issue.
What is post-segregational killing?
Sometimes the plasmid can impose stress on the bacteria and may slow the growth of the bacterial cell, to an extent where the plasmid free cells out-compete them. Will kill the cell, lyse, and be taken up via transformation to other cells. Can do this by producing both a toxin and resistance to this toxin
What is an example of how plasmids contribute to bacterial evolution?
The movement of plasmids is arguably the largest contributor to genetic and phenotypic diversity in bacterial cells. Providing genotypes that selection can actually act upon.
