Question

5'-end capture occurs only in the ______ model?

a) Double-strand break repair model
b) Synthesis-dependent strand-annealing model
c) Single-strand annealing
d) Break-induced replication

Answer 1

5'-end capture specifically occurs in the synthesis-dependent strand-annealing (SDSA) model of DNA repair. Different from other models, SDSA allows for repair without crossover events which might lead to recombination, preserving the original genetic information.

Step-by-step explanation:

5'-end capture occurs only in the synthesis-dependent strand-annealing (SDSA) model.

In this model of repair, a single-stranded break is processed by enzymes to generate a region of single-stranded DNA. The RecA protein, crucial in homologous recombination, binds to this single-stranded DNA, forming a structure called a nucleoprotein filament, which searches for a homologous sequence to base-pair with. After finding the sequence, the DNA strand is extended, leading to strand annealing and repair. In other repair models, such as double-strand break repair (non-SDSA), this 5'-end capture mechanism is not predominant.

Double-strand break repair, another example of homologous recombination, differs from the SDSA model. It can involve the formation of a Holliday junction, which can be resolved in a cross-over event, potentially leading to genetic recombination between non-sister chromatids.