Continuity mistake: Just after Lockdown stabs Optimus in the chest with his own sword, Cade runs closer and shoots at Lockdown. He then hides behind some bricks. In that shot, the bricks are a broken wall that is two separate pieces. Then it cuts to a different shot as Lockdown returns fire at Cade, and now the wall is one piece. A guy also suddenly appears in the shot next to the wall and right where the explosion happens where Lockdown shot the wall. Originally, this man was one of several extras portraying the silo factory workers wearing hard hats, who were running and hiding, but Michael Bay wanted this silo scene to be about just the main cast, so the scene was trimmed and the extras were cut, but this shot slipped through. Some footage can be seen on Blu-ray special features. (02:30:55)
Answer: Optimus was being dramatic when he said it contained their memories. Transformers don't carry their memories in their spark any more than humans carry theirs in their soul.
MasterOfAll