I noticed it would give a little jerk as it was changing into another gear

Every now and then while driving my car I noticed it would give a little jerk as it was changing into another gear. My car is an automatic. It doesn't do it often and it wasn't hardly noticeable when it did. One day while driving and in the Drive gear, it just stopped going. It did not shut off, it just acted like it slipped into neutral and was just idling. When moving the shifter column into the gears it does not engage into any of them. Do I need to replace my entire transmission or is it something else within the transmission?