Abstract: A laboratory processing tube assembly mounts to a processing unit for dissociating an organically derived sample. The tube assembly includes a tube and a cap that form a tube chamber that contains the sample during dissociation. The tube includes at least one internal thread extending inwardly from and peripherally about its inner surface in a helical arrangement, with the internal helical thread including a ridge defining two impact surfaces facing in generally opposite directions, and with a first one of the impact surfaces impacted by the sample as the sample flows in a first axial direction in the tube chamber and a second one of the impact surfaces impacted by the sample as the sample flows in a second opposite axial direction in the tube chamber during axially-reciprocal tube-assembly motion to dissociate the sample.