Plasmid

Plasmid

An independent piece of DNA not associated with the bacterial chromosome (circular and smaller)

• carries genes just like bacterial chromosome does

• the genes are nonessential

Conjugative Plasmid

Carries genes for s*x pili and transfer of the plasmid

Dissimilation plasmids

Encode enzymes for catabolism of unusual compounds

R factors

Encode antibiotic resistance

Transposon

“Jumping genes”

• segments of DNA that can move from one region of DNA to another

• mediated through an enzyme called transposase

• Targets a sequence of DNA and cuts it, allowing for the incorporation of DNA into a different region

• It reseals the DNA after

Plasmids and transposons…

allow bacteria to rapidly acquire, accumulate, and share resistance to drugs.

• Transposons physically "cut and paste" antibiotic resistance genes from the main bacterial chromosome and insert them directly into plasmids.

• Plasmids then transport these genes between different bacteria

Recombination

Exchange of DNA and incorporation of it into the host chromosome/genome

Transformation

Cell incorporates a piece of external DNA into the cell.

• movement of “naked” DNA between cells

Transformation requires

receptors for DNA incorporation

Competent bacteria

bacteria that have the receptors required for transformation

Transformation in a laboratory sense

Holes in the cell membrane can induce cells to allow DNA in

• laboratory setting through heat, electric shock, chemicals,

Conjugation requirements

Requires direct contact between cells

• the cells have to be of opposing mating type (one carries the plasmid and the other doesn’t)

Requires pilis - allows for transfer of material

F factor

• Plasmid because genes lie on it, meaning it can engage in conjugation

F+ cell

A cell carrying a plasmid for conjugation

F- cell

A cell without a plasmid

• the plasmid is transferred to the recipient F- cell during conjugation, turning it into an F+ cell.

High frequency recombinant (Hfr) cell

Occurs when the F factor (plasmid) becomes integrated into the chromosome

Transduction

Utilizes a virus as the means to transfer DNA between cells

• no cell to cell contact required

• the infection process in a cell is required

Bacteriophage

a virus that targets only bacteria

Transduction process

1. Bacteriophage delivers its own genetic material into the cell

2. Codes for proteins that break the host chromosome down

3. Occasionally during phage assembly, pieces of bacterial DNA are packaged in a phase capsid.

• the donor cell lyses and releases phage particles containing bacterial DNA

4. A phage carrying bacterial DNA infects a new host cell, the recipient cell.

5. Recombination can occur

• produces a recombinant cell w/ genotype different from both the donor and recipient cells.