SANTA CLARA – Alex Smith is one of 12 NFL quarterbacks who started every regular-season game in 2011.

But you only need to watch the exhibition season opener against the Saints to realize just how tenuous that accomplishment is. Smith was walloped four times in the first half of that game, and any one of those hits could have caused an injury that would have sent the 49ers' season on an entirely different tangent.

The X factor as the 49ers start their playoff run Saturday at Candlestick Park is Smith's backup, Colin Kaepernick. The second-round draft pick played 20 snaps during the regular season and attempted five passes. The 49ers' No. 3 quarterback, Scott Tolzien, also is a rookie, and he's been inactive for every game this season.

Coach Jim Harbaugh and the 49ers gambled by having two rookies behind Smith, and the stakes became higher when the 49ers made the playoffs. But having a backup with little experience isn't especially unusual during the 2011 postseason.

Of the seven other teams still in the Super Bowl hunt, three have No. 2 quarterbacks with no starting experience, including New Orleans backup Chase Daniel, a third-year player who has attempted eight regular-season passes during his career.

One of the other teams also has a rookie as a backup. That's Tyrod Taylor, a sixth-round draft choice who plays for coach John Harbaugh and the Baltimore Ravens.

Another rookie, T.J. Yates, is starting for the Houston Texans.

As with most 49ers rookies, Kaepernick has spent more time at the team facility in Santa Clara than he has in his own apartment, which is just a mile and a half away, since the lockout ended in late July. Kaepernick's friend on the team, fellow rookie Bruce Miller, said the quarterback has only four items in his apartment: a bed, a television, about 300 baseball caps and about as many shoes.

"He doesn't have much in there," Miller said. "There's been a lot of time spent here by a lot of guys, and we've seen the results by going 13-3."

There have been some changes in the lanky quarterback from Turlock. Offensive coordinator Greg Roman said Kaepernick's throwing motion, criticized before the draft for being too elongated, has been shortened. Still, Roman said the 49ers did not want to make Kaepernick's release too cookie- cutter.

"Most quarterbacks that are very productive in this league can utilize various arm angles to throw the football," Roman said. "I think the guy we're playing (Saints starter Drew Brees) has demonstrated that a lot. He can throw the ball and release it however he needs to. That's something that you're always trying to do – put more clubs in your bag."

The way Kaepernick watches games also has changed. When the season began, he studied Smith and concentrated on how the seven-year veteran would handle certain situations. Smith, however, stressed to him the importance of seeing the entire field, and now Kaepernick watches the defense and how a play unfolds.

"It's not about seeing little things here and there," he said. "It's being able to open your eyes and see everything as a whole."

Said Miller, who's been working out with Kaepernick since June: "My first impression of Colin was that he was an athlete, not a quarterback. Now he's a quarterback and an athlete. He's grown so much."

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