8.592J | Spring 2011 | Graduate

Statistical Physics in Biology

Lecture Notes

Molecular Motors & Cell Motility

Molecular Motors

  1. Molecular motors:   

  2. General scheme of motor transport:   

    • Asymmetry for directionality
    • Rectification of fluctuations by consumption of energy
  3. Motion in a noisy environment   


A Brownian ratchet (Image from Wikimedia Commons)

View a ratchet and pawl animation

  1. Asymmetric hopping models:
    • Fisher, M. E., A. B. Kolomeisky. “The force exerted by a molecular motor.” PNAS 96, no. 6597 (1999).
    • Multiple internal states
    • Solution with two internal state
    • Einstein force, stalling force

Cell Motion

  1. Brownian motion
  2. Crawling cells
  3. Swimming cells:
    • Life at Low Reynolds Number (E.M. Purcell)
    • The scallop theorem: impossibility of reciprocal motion
    • Flagellar rotary motion (efficiency)
    • Chemotaxis by runs and tumbles—why?

(Detailed Lecture Notes (PDF))

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Spring 2011
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