# Molecular Motors & Cell Motility

## Molecular Motors

1. Molecular motors:
   - Kinesin and Dynein move in opposite directions along microtubules consuming ATP
   - Myosin moves on actin filaments
   - Animation of motion of kinesin on a microtubule
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

- Feynman's ratchet and pawl:
- Simulation of a Brownian motor
- From the web-page of George Oster:
  - Wang, H., and G. Oster. "Ratchets, power strokes, and molecular motors." (PDF) Applied Physics A 75, no. 315 (2002).
  - Bustamante, C., D. Keller, et al. "The Physics of Molecular Motors." (PDF) Acc. Chem. Res. 34, no. 412 (2001).
  - Animation of energy landscape for a rotary motor

- 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

## Some Related Links

- Kinesin Home Page
- Dynein Home Page
- Myosin Home Page
- Kinesin Motors—the Movies
- Vale lab movies (e.g. MT gliding)
- The inner life of a cell
- Lecture at Delft by Gerrit E.W. Bauer
- Capturing and viewing single molecules:
  - Optical tweezers
  - Fluorescent light microscopy (PDF)

## Cell Motion

1. Brownian motion:
   - Movies of milk droplets in water, DNA tethered bead
   - Animated simulation (see also Applet 1, Applet 2)
   - Langevin description
   - Fokker-Planck description
   - Thermal equilibrium and the Einsten relation
2. Crawling cells
   - Remodelling of actin cycloskeleton
   - Crawling Neutrophil Chasing a Bacterium
   - Actin-based motility (Listeria)
   - More from the Theriot lab movie collection
   - Latex beads coated with ActA protein: motion and spontaneous symmetry breaking
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?

## Some Related Links

- Cell Locomotion
- Some parameters for diverse Cell Motion
- E. M. Purcell. "The efficiency of propulsion by a rotating flagellum." (PDF) PNAS 94, (1997): 11307–11.
- Berg, Howard. "Motile Behavior of Bacteria." Physics Today, January 2000, 24.

(Detailed Lecture Notes (PDF))