The commercial pilot was maneuvering around clouds during a skydiving operation when the airplane abruptly made a steep bank to the left and continued to dive. He made control corrections to recover the airplane and soon after landed uneventfully. The pilot believes that he hit a patch of turbulence that caused the airplane to maneuver in such a manner. The pilot was a new skydiving pilot and was inexperienced with flying an airplane loaded with jumpers. The post incident examination revealed minor damage to the airplane.