Like college students submitting last-minute classwork, candidates scurried to the Minnesota secretary of state's office to file their official paperwork before Tuesday's deadline.

The close of filing highlights a few trends that will keep voters watching through the year:

U.S. House primaries

• Voters in August will decide which Democrat will challenge U.S. Rep. Chip Cravaack, a Republican, for northern Minnesota's Eighth District and which Republican will challenge U.S. Rep. Tim Walz, a Democrat, for southern Minnesota's First District. Republicans Allen Quist and Mike Parry are vying to take on Walz; DFLers Rick Nolan, Tarryl Clark and Jeff Anderson are battling over who will run against Cravaack. Neither Cravaack nor Walz has primary challenges.

• Five sitting members of the U.S. House -- Republicans John Kline, Michele Bachmann and Erik Paulsen and Democrats Betty McCollum and Keith Ellison -- will have primaries. None of the challengers to those five has raised significant resources or has large a campaign organization.

Legislative primaries

• Rep. Connie Doepke, R-Orono, will run for state Senate against the GOP-endorsed candidate, David Osmek.

• Rep. Steve Smith, R-Mound, will run for his seat in a primary against Republican-endorsed Cindy Pugh. Smith, trying for an 11th term, lost his committee chairmanships last session and failed to get endorsement.

• There is a three-way DFL race to replace retiring Rep. Tom Rukavina of Virginia.

• Deputy Senate Majority Leader Julianne Ortman, of Chanhassen, will face off in a Republican primary against Bruce Schwichtenberg. Neither has GOP endorsement.

• DFL Sen. John Harrington, after being passed over for endorsement, recently announced his retirement, triggering a four-way primary in St. Paul to replace him.

Up and out

• Thirty-six legislators have opted not to run for another term. Nine House members are trying to move up to the state Senate.

• Nine people want to be Minnesota's next U.S. senator. U.S. Sen. Amy Klobuchar, a Democrat, will face off against three challengers in an August primary: fugitive felon Jack Shepard, who lives in Rome, and Dick Franson, who has run for more than two dozen offices and only won once -- for Minneapolis alderman in the 1960s, and Darryl Stanton, who was DFL endorsed a decade ago to run against then-U.S. Rep. Jim Ramstad, a Republican. Stanton, who was the last person to file for office Tuesday, said he wanted to run as an independent but lacked the needed signatures so decided to run as a DFLer. Republican-endorsed candidate Kurt Bills, a state representative, faces a three-way primary with Bob Carney, a frequent candidate, and David Carlson, who has run for the Legislature before. Glen Menze, who has run against Democratic U.S. Rep. Collin Peterson as a Republican, is running with the Independence Party, as is Stephen Williams, whose campaign website says he is running for lieutenant governor.

• Four lawmakers are living the dream of every candidate: Sen. Kathy Sheran, DFL-Mankato; Rep. Mike Nelson, DFL-Brooklyn Park; Rep. Joe Hoppe, R-Chaska, and Rep. Tony Cornish, R-Good Thunder, drew no opponents.

Rachel E. Stassen-Berger Twitter: @rachelsb