Answer based on context:

Still looking for a win the 49ers flew to Georgia Dome for an NFC duel with the Falcons. In the first quarter the 49ers took the early lead with QB Alex Smith making a 12-yard TD pass to TE Vernon Davis. Then DB Taylor Mays recovered a blocked punt in the endzone for a touchdown. Then the Falcons rallied with QB Matt Ryan completing an 8-yard TD pass to WR Harry Douglas. Then the Falcons took the lead with three field goals from kicker Matt Bryant. He made a 37-yard field goal near the end of the 2nd quarter, a 31-yard field goad in the 3rd.  Late in the 4th quarter, CB Nate Clements intercepted Matt Ryan's pass which should have sealed the game for the 49ers who were then up 14 - 13.  However, instead of going down, Clements continued down the left sideline attempting to score.  He would return the interception 39 yards before Falcons WR Roddy White was able to strip the ball from him and the Falcons recovered the fumble.  After regaining possession, the Falcons drove down the field again and this time was able to win the game on a 43-yard field goal by Matt Bryant, giving the 49ers another loss.

Who threw the longest touchdown?
Alex Smith