Final answer:
The correct answer is option c. The incorrect step in the SOS repair system is the claim that after damage, RecA is continuously activated making the SOS response irreversible. In reality, the SOS system can be turned off after DNA repair is complete, restoring normal cell functions.
Step-by-step explanation:
The SOS repair system is a pathway for repairing DNA damage in bacteria. During the SOS response, several DNA repair enzymes are induced to address damage caused by extracellular factors like UV radiation. The step that is NOT a part of the SOS repair is option C: 'After damage, RecA is continuously activated and, therefore, SOS response is irreversible.' This statement is incorrect because the SOS response is not irreversible; once the DNA damage is repaired, the RecA protein ceases its stimulatory role, LexA accumulates again and represses the SOS genes, thus the cell returns to its normal state.
Other aspects of SOS repair include: the induction of the RecA and LexA genes, the self-cleavage of the LexA repressor which de-represses the SOS genes, and the regulation of the expression of enzymes involved in excision repair. These enzymes participate in various forms of DNA repair mechanisms, including homologous recombination, an evolutionarily conserved process evident from the shared function of bacterial RecA with its homologs like Rad51 in humans.