Transduction & Plasmids/Transposons

Transduction by a bacteriophage

Virulent phages perform generalized transduction (rare occasions 1 in 100,000,000); random fragment of host cell dna ends up in phage during packaging

lysogenic cycle

Specialized transduction results in transfer of specific genes

One of the most studied temperate viruses is

Phage lamba

mobile genetic elements

move from one chromosome to another or from one cell to another and occur in prokaryotic and eukaryotic organisms

mobile genetic elements examples

Plasmids and transpsons

Plasmids

small circular DNA molecules that replicate separately from the bacterial chromosome

Plasmids often code for

proteins that enhance the pathogenicity of a bacterium

Plasmids size

1 to 5% the size of a bacterial chromosome

conjugative plasmid

carries genes for sex pili and transfer of the plasmid

Dissimulation plasmids

encode enzymes for catabolism of unusual compounds

Resistance factors (R factors)

encode antibiotic resistance

Transposons

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

Transposons contain

insertion sequences (IS) for cutting and resealing DNA (transposase)

complex transposons

carry other genes (e.g, in antibiotic resistance)

Genes and evolution

Mutations and recombination create cell diversity

Diversity is the

Raw material for evolution

Natural selection acts on

Populations of organisms to ensure the survival of organisms fit for a particular environment