8.592 - HST.452J (Spring 2024)

Statistical Physics in Biology

Lecture 18

Molecular Motors

1. Molecular motors:
   • Kinesin and Dynein move in opposite directions along microtubules consuming ATP
   • Myosin moves on actin filaments (offline animation) [youtube]
   • Motion of kinesin on a microtubule (Vale lab) (offline animation)
2. General scheme of motor transport:
• Asymmetry for directionality
• Rectification of fluctuations by consumption of energy
3. Motion in a noisy environment

• Feynman's ratchet and pawl:  (youtube)                
•       (R. Di Leonardo, et al PNAS 2010)
• Simulation of a (flashing ratchet) Brownian motor      (flashing ratchet video)   (Brownian Ratchet)
• From the web-page of George Oster:
  • "Ratchets, power strokes, and molecular motors," H. Wang & G. Oster, Appl. Phys. A 75, 315 (2002).
  • "The physics of molecular motors," C. Bustamante, D. Keller, & G. Oster, Acc. Chem. Res. 34, 412, (2001),

• Asymmetric hopping models:

• "The force exerted by a molecular motor," M.E. Fisher & A.B. Kolomeisky, PNAS 96, 6597 (1999).
• Multiple internal states
• Solution with two internal state
• Einstein force, stalling force
• Efficiency at maximum power; T. Schmiedl & U. Seifert EPL

(Lecture notes)

Some related links

• Kinesin Home Page
• Kinesin Motors - the Movies
• Vale lab movies (e.g. MT gliding)
• The inner life of a cell
• Capturing and viewing single molecules:
  • Optical tweezers
  • Fluorescent light microscopy
• "Ratchets, power strokes, and molecular motors," H. Wang & G. Oster, Appl. Phys. A 75, 315 (2002).
• "The physics of molecular motors," C. Bustamante, D. Keller, & G. Oster, Acc. Chem. Res. 34, 412, (2001),

1. Brownian motion: (offline)
   • Movies of  milk droplets in water,
   • Brownian motion simulation
   • Langevin description
   • Fokker-Planck descrition
   • Thermal equilibrium and the Einsten relation
   • Lecture notes on Dissipative Dynamics
2. Crawling cells
   • Crawling Neutrophil Chasing a Bacterium
   • Actin-based motility (Listeria)
   • More from the Theriot lab movie collection
3. Swimming cells:
• Life at Low Reynolds Number (E.M. Purcell)  (offline)
• The scallop theorem: impossibility of reciprocal motion
• Flagellar rotary motion (efficiency)
• Chemotaxis by runs and tumbles- why?

Some related links

• Cell Locomotion
• Some parameters for diverse Cell Motion
• "The efficiency of propulsion by a rotating flagellum," E.M. Purcell, PNAS 94, 11307 (1997).
• "Motile behavior of bacteria," (Physics Today, Howard Berg).