Had this problem on a 2005 grand prix, The Bolt that is on the control arm that holds the pivot assembly ( Right under the wheel bearing ) was loose, this will cause jerking, hard turning and pulls. You may also want to check alignment and check steering rack. The best test is to test the car at a stop while on and see if the same issue occurs, if it does then there is probley a problem with a the steering rack, if it does not then alignment or control arm issue is normally the culprit. Hope this helps - just past experiences.
