Question

List conditions of site-specific recombination that result in integration, excision, and inversion respectively, in terms of the shapes of DNA and orientations of the target site.

Answer 1

Okay, first of all, let's define site-specific recombination: These are DNA recombination events in which an specific enzyme (recombinases). There are specific site to indicate where to cleave, the target sites.

This is a topological matter, and the resulting type of recombination depends on the orientation of the recombination target sites. which are the specific locations where recombinases act.

Integration: The recombinations sites must be located in different molecules. The shape of at least one of the molecules has to be round, a circular chain

Excision: Both recombination sites have to be located on the same molecule, and the sites have to be in the same orientation (direct repeats). A loop forms to closen the target sites, the loop gets cleaved and the main DNA strands rejoin, cutting apart the intermediate sequence.

Inversión: Both recombination sites have to be located on the same molecule, and the sites have to be inverted in orientation (inverted repeats). A loop forms to closen the target sites, the loop gets cleaved and then is retaken and rejoined by the opposite main strand. That is posible because of the target site orientation, the palindrome is recognized in the other end of the cleaved loop and retaken