Question

Compare and contrast homologous recombination and site specific recombination. Address their principles, molecular mechanisms, and physiological functions

Answer 1

Homologous recombination Vs Site-specific recombination

Homologous recombination:

?Principle- It is the exchange of genetic material between two DNA strands containing long stretches of similar base sequences.  

Mechanism- It can be divided into three key steps: strand exchange, branch migration, and resolution. Strand exchange involves the pairing of the broken DNA end with the homologous region of its sister chromatid, followed by strand invasion to form a Holliday junction. During branch migration, the Holliday junction is translocated along DNA, extending the region of heteroduplex away from the initial crossover site. Finally, the Holliday junction intermediate is resolved by cleavage of the junction to form separate recombinant duplex DNA molecules again.

Physiological functions- In bacteria and eukaryotes, it is a major mechanism of DNA repair. In genetic engineering, it is used as a form of gene targeting.It is also responsible for shaping viral evolution.

Site-specific recombination:

Principle- It involves the exchange of DNA strands between segments possessing a certain degree of sequence homology.

Mechanism- The process involves two DNA strands, a specialized recombinase protein which recognizes the sites and a mechanism involving DNA breakage and reunion restoring the phosphodiester bond energy.The recombinase binds to the two recombination sites. The two recombinase-bound sites pair, forming a synaptic complex with crossover sites juxtaposed.The recombinase then catalyzes cleavage, strand exchange, and the rejoining of the
DNA within the synaptic complex. Finally, the synaptic complex breaks down, releasing the recombinant products.

Physiological functions- It plays a crucial role in a variety of cellular processes including bacterial genome replication, differentiation, and pathogenesis and the movement of mobile genetic elements.It is quite a powerful tool in genetic engineering.