L14 - Plasmids

Plasmids

Extrachromosomal, self-replicating DNA molecules

Methods of plasmid replication

• Theta replication (unidirectional or bidirectional)

• Rolling circle

Rolling Circle

Mechanism of DNA replication where a single strand is nicked and unwound, allowing for continuous synthesis of a new strand.

Host range

Species of bacteria in which the plasmid can replicate

Broad host range

Replicate in many species, and often encode their own replication proteins

Narrow host range

Restricted to a single species and often rely on host proteins for replication

Copy number

Average number of a single plasmid type per cell

Incompatibility Groups

Categorisation of plasmids that cannot coexist in the same host cell due to similar replication control mechanisms.

Conjugation

The ability of some plasmids to transfer themselves & other DNA elements from 1 cell to another

Transconjugant

The recipient cell that has received a plasmid through conjugation.

Promiscuous plasmids

Conjugative plasmids that can move DNA between unrelated species

Mechanism of Conjugation

• The donor cell produces a pilus

• Pilus contacts a potential recipient that doesn’t contain a plasmid

• Retraction of pilus brings cells into contact

• Pore forms in adjoining cell membrane

• Rolling cell replication

• New DNA strand is synthesised in the donor

Transformation

The process by which a cell takes up foreign DNA from its environment, leading to a change in its genotype and phenotype.

Competent Bacteria

Bacteria that are capable of taking up foreign DNA during transformation.

Transformant bacteria

Bacteria that have successfully incorporated foreign DNA into their genome during transformation.

Ligation

The process of joining two fragments of DNA together, typically using an enzyme called DNA ligase. Ligation is commonly used in recombinant DNA technology to create plasmids.

Forward Primer

A short single-stranded DNA sequence used in PCR to initiate DNA synthesis. It anneals to the template DNA at the beginning of the target region.

Reverse Primer

A short single-stranded DNA sequence used in PCR that binds to the complementary region of the template DNA, allowing for the synthesis of the target DNA strand.

Restriction Enzyme

Bacterial enzymes that restrict possibility of attack from foreign DNA