Shameless Sunday at 9 p.m., Showtime

Every time I see Emmy Rossum all prettied up at some awards show or singing opera or pop on some talk show, I am reminded of how profoundly she transforms herself to play Fiona. She gives one of TV’s great underappreciated performances on “Shameless,’’ as the oldest sibling and caretaker of the Gallagher family. She puts her body and soul into the role, bouncing off walls as life throws one curveball after another at her. Fiona is both a responsible adult and a girl struggling with a legacy of self-destruction, and Rossum makes those conflicting qualities work together effortlessly. Like almost every actor on this spirited show, she has been unfairly ignored by awards voters. TV acting doesn’t get much more genuine, both in terms of comedy and drama, than it is on “Shameless.’’

American Masters: Mike Nichols 9 p.m., WGBH 2

Mike Nichols’s former comedic partner, Elaine May, directs this profile of the man behind “The Graduate,’’ “Who’s Afraid of Virginia Woolf,’’ and “Working Girl,’’ among many others. The list of interviewees isn’t too shabby: Meryl Streep, Steven Spielberg, Tom Hanks, Dustin Hoffman, Alec Baldwin, Paul Simon, Matthew Broderick, Nathan Lane, Bob Balaban, Tony Kushner, Neil Simon, Frank Langella, and James L. Brooks.

Downton Abbey Sunday at 9 p.m., WGBH 2

Now her empty cup is as sweet as the punch.

MythBusters Saturday at 8 p.m., Discovery

I ain’t afraid of no myth.

Mercy Street Sunday at 10 p.m., WGBH 2

Wear your inside out.

Matthew Gilbert can be reached at gilbert@globe.com. Follow him on Twitter @MatthewGilbert.