MODELING ELASTIC PROPERTIES OF MICROTUBULE TIPS AND WALLS

Electron micrographs of tips of growing and shrinking microtubules are analyzed and interpreted. The many shapes observed are all consistent with a simple mechanical model, a flexible tube with competing intrin sic curvatures. Observations are also consistent with growing and shri nking microtubules having the same intrinsic curvature for protofilame nts, the one observed in oligomers peeling off shrinking microtubules. If this is so, the lateral bonds between protofilaments are responsib le for the difference between shapes of tips on growing and shrinking microtubules.