"column does not exist" using PostgreSQL

Error:

psycopg2.ProgrammingError: column "marcos" does not exist
 LINE 1: ...RT INTO user_table (nome, usuario, senha) VALUES ("marcos", ...
                                                              ^

Code:

cur.execute('INSERT INTO user_table (nome, usuario, senha) VALUES ("marcos", "marcosturossi", "1234")')

I have tried in many ways but I can not add data to the database in python!