What step would likely be affected if the bacteria are exposed to this antibiotic

bacteria subjected to an antibiotics will have their ribosomes inhibited whixh will stop them from synthezing proteins which stops the possibility of reproduction and many other vital functions.

I disagree with the current answer. I believe the answer is the one you have selected. This is because the three domains of life are separated into 3 categories, bacteria, archeabacteria, and eukaryotes. Archeabacteria are prokaryotic, and possess no true nucleus.