Here is a list of typical DBA responsibilities:

Installation, configuration and upgrading of Oracle server software and related products

Evaluate Oracle features and Oracle related products

Establish and maintain sound backup and recovery policies and procedures

Take care of the Database design and implementation

Implement and maintain database security (create and maintain users and roles, assign privileges)

Perform database tuning and performance monitoring

Perform application tuning and performance monitoring

Setup and maintain documentation and standards

Plan growth and changes (capacity planning)

Work as part of a team and provide 7x24 support when required

Perform general technical trouble shooting and give consultation to development teams

Interface with Oracle Corporation for technical support.

Monitor alert logs, trace files, listener logs, etc.