Models for Molecular Movement (IMAGE) University of Pennsylvania School of Medicine Caption Possible models for the bi-directional movement observed in the dynein-dynactin molecular motor along microtubules. A) Random, diffusive motions; B) Flexible rotation of the dynein ring; and C) Steps dictated by the microtubule lattice. Credit Credit: Jennifer L. Ross, PhD, University of Pennsylvania School of Medicine; Nature Cell Biology Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.