Final answer:
RecA-dependent strand exchange cannot occur between circular DNAs but can occur between linear DNA molecules.
Step-by-step explanation:
RecA-dependent strand exchange cannot occur between two homologous, double-stranded, covalently closed, circular DNAs (cccDNAs) because the double-stranded structure of the cccDNAs prevents the RecA protein from accessing and binding to the DNA strands for strand exchange to occur. The circular structure of cccDNAs hinders the unwinding and separation of the DNA strands required for RecA-mediated strand exchange. On the other hand, strand exchange can occur between two double-stranded DNA molecules pictured in Figure 11-8c because the linear nature of the DNA molecules allows for the unwinding and separation of the DNA strands, enabling RecA to bind and facilitate strand exchange.