Hello dear
Marks required in neet for a seat in some of the top medical colleges in Tamil Nadu are given below for general , obc , sc and st category respectively under all India quota.
Bangalore Medical College and Research Institute, Bangalore-512(general ),445(obc) ,407(sc),  375(st)
Mysore Medical College, Mysore-503,488,446,349
So dear try to score 500 + marks to get a seat in best Medical College of Tamil Nadu if you are from general category.
Feel free to ask your further queries if any.

For getting into any government medical college, you should have a score of 550+ in NEET. Also, the competition for those seats in government colleges is very very high, so yes 550+ is the minimum requirement. But depending upon your category it may be variable. If you belong to SC/ST it should be 450+, for OBC it is 500+ or else for general it is 550+.