Bio March 19

Plasmid Integration and Freeing Process

• Plasmid Integration:

• A plasmid can remain as an independent entity or can integrate into the bacterial genome through specific insertion sites.

• In the case of ethanol, plasmids insert themselves into the bacterial genome using insertion sites that typically have high affinity for integration.

• Freeing from Bacterial Genome:

• When a plasmid that has integrated into the bacterial genome decides to revert to a plasmid state, it loops back on itself through its insertion site, resulting in a clean cut.

• This freed plasmid is referred to as an f plasmid (fertility plasmid).

F' Plasmids and R Plasmids

• Fprime Plasmids:

• When the plasmid frees itself but captures some of the host's DNA during the process, it is referred to as an f prime plasmid (F').

• The nomenclature is based on the specific genes it retains, e.g., F' lac if it includes the lactose gene.

• F’ plasmids can carry multiple genes and mark them according to their order and position relative to the original f plasmid (e.g., F' lac, F' gal).

• R Plasmids:

• If the plasmid contains antibiotic resistance genes, it is called an R plasmid (R for resistance), which is significant for the spread of antimicrobial resistance.

• R plasmids play a vital role in gene transfer in bacterial populations, making the study of their spread crucial.

Transformation

• Definition:

• Transformation is the process where a bacterial cell takes up DNA from its environment without direct physical contact with another cell.

• It often occurs when a bacterial cell lyses (breaks down), releasing its genomic material into the surroundings, which can then be absorbed by other nearby bacteria.

• Mechanism:

• DNA enters through natural pores on the bacterial membrane and can recombine with the recipient cell's genome.

• Competence in Bacteria:

• Some bacteria are naturally competent and can readily take up DNA.

• In laboratory conditions, cells can be treated to make them competent, allowing for more efficient DNA uptake.

• Cotransformation:

• The probability of cotransformation is related to the spatial arrangement of genes; genes that are closer together have a higher chance of being transformed together.

• For instance, if genes A, B, and C are studied, A and B will more likely cotransform than A and C if they are closer together on the genome.

Transduction

• Definition:

• Transduction involves the transfer of genetic material between bacteria via a bacteriophage (a virus that infects bacteria).

• Mechanism:

• A bacteriophage infects a bacterial cell, injects its DNA, and hijacks the host's cellular machinery to produce viral components.

• The phage can sometimes mistakenly incorporate pieces of the host's DNA during viral assembly and transfer this DNA during subsequent infections.

• **Types