This article does a great job breaking down TCU's defense under Gary Patterson. Some of the info was included in UStreet's great breakdown from earlier this week, but there are additional play by play examples that make it worth reading anyway. I couldn't hope to excerpt what you need, so enjoy the blurb below and then go read the whole thing!
By playing five defensive backs, Patterson almost never needs to substitute to match up with the offense. But the system’s genius runs even deeper: Patterson has cleaved the very structure of his defense into pieces, simultaneously making everything simpler for his players and more complicated for opponents.