2001 Saturn missfire

The fuel filter and the O2 sensors shouldn't be isolating the misfire to one cylinder.

What did the plug look like from that cylinder compared to the other?

Carbon build up in normal (typical)-yes, but leads to problems.
Cancer is typical (normal?) But lead to problems.
Do you know what I mean? Normal is relative to the situation. This is my carbon removal technique that works for me:

Air induction service:
I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have someone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushings. Seafoam is another good product, but smokes a lot.

IF you can't find Castle, here is my rep's email:
robw@castlepackspower. Com

I am trying to find out why just the # 4 cylinder is the problem. Was the number 4 cylinder coil "electrode" any differnet than the others?

Try swapping the number 4 injector with the number one injector. If the mis fire moves to the number one cylinder, you have your answer :)