Mobile Elements, Gene Regulation & Viral Genetics
Transposons, restriction-modification and CRISPR, lac and trp operon genetics, prophages, Hershey-Chase, complementation, and viral mutation, recombination and reassortment
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Mobile Elements, Gene Regulation & Viral Genetics
Mobile DNA, Defense & Operons
Transposons move DNA within one cell; a composite transposon carries cargo such as resistance between two IS elements, and an insertion can knock out a gene or silence those downstream of it. Restriction enzymes cut unmethylated copies of their site (innate defense); CRISPR stores spacers from past invaders and guides Cas to cut them (adaptive, heritable). Lac is inducible: allolactose releases the repressor, and CAP-cAMP activates it when glucose is low. Trp is repressible: tryptophan is the corepressor. Repressors act in trans; operators act in cis.
Viral Genetics
DNA damage destroys the phage repressor and induces a prophage. Hershey-Chase showed DNA, not protein, enters and is inherited. Complementation in nearly every co-infected cell places mutations in different genes; rare heritable wild type is recombination. Unproofread RNA copying drives antigenic drift; swapping whole segments (reassortment) drives antigenic shift.
Key Takeaways
- Transposition is a within-cell move; plasmids move genes between cells.
- Proteins act in trans, DNA sites in cis.
- Only segmented viruses such as influenza can shift.
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