Final answer:
Cutting pUC19 with PstI would result in a single band on an agarose gel, as this plasmid has only one PstI recognition site which would linearize the plasmid when cut.
Step-by-step explanation:
When pUC19 is digested with the restriction enzyme PstI, the number of bands you would expect to see on a gel depends on the number of PstI recognition sites present within the plasmid. pUC19 is a commonly used plasmid vector in molecular biology due to its high copy number and the presence of lacZ for blue/white screening of recombinant clones. In the case of pUC19, there is only one PstI recognition site.
After complete digestion with PstI, you would expect to see a single band on an agarose gel representing the linearized plasmid DNA. This occurs because the one PstI site is cut, leaving no multiple fragments but a single linear piece of DNA. If the plasmid were not fully digested, or if there were additional sites for PstI, you may see multiple bands or the original supercoiled plasmid as additional bands on the gel.