Forum:Missing pieces

--Spoiler alert-- Hey guys. This week I've finished both Mass Effect and Mass Effect 2. Everything seems fine with Mass Effect, but when I finished Mass Effect 2 and read some info I've noticed there were some missing prieces to it. I had read, that in the end I was suposed to destroy the Alpha gate(don't know if thats what it's actually called, I read this info in Lithuanian), kill 300 000 batarians in the process and stand trial afterwards. While this is happening, Reapers attack Earth, Shepard escapes and seeks help from other races. But my last mission was The Suicide Mission, where I had to destroy a human-reaper and after that mission the game was over, the credits appeared. Now can someone help me, tell me what is the problem, do I need download some expansion or do I need to complete some additional missions for this to happen? I'feel kind of silly asking this, but I think this is the fastest way to find out, so please, help me out guys! Appreciate it :)