Thursday, September 30, 2010

Myosin and actin are the force generating units of muscle fibres

The most intuitive example of a motor in the human body would be the skeletal muscles. When researches were using optical and electron microscopy to study the muscle fibres they found that at each level of resolution the larger unit was made up of smaller force-generating subunit. At the molecular level myosin and actin were found. See Fig 10.1 pp405: muscles -> muscle fibres bundle -> individual muscle fibres -> myofibril -> myosin filament & F-actin filament -> myosin molecule & G-actin molecule.

The first experiment to provide direct proof of the force generation of myson & actin was by Finer et al., 1994 here they used the familiar combination of adhesion to glass beads which are trapped by optical tweezers which can measure force. When ATP was added to the setup shown in a. a sideways displacement of the actin filament was inferred by the measurement of a force in b.

Figure 10.2 provides a good summary of the experiment.

As this technique seems to be fairly common (optical tweezers + glass bead adhesion) I am wondering how they get the molecules to adhere to the glass?


  1. I too don't know exactly how this is done. But we have to remember that glass may look smooth to us, but is really covered in millions of microscopic cracks. It is reasonable to assume that if the glass was coated in some substance that the DNA can bind to (perhaps even just a viscous liquid with a positive charge) then some of the anchoring molecule would get stuck in those cracks.

  2. Yes but it would presumably have to be stronger than the weak interactions which attach myosin to actin otherwise it would be removed from the bead under strain. I just read in Finer et al. Nature 368, 113 - 119 (10 March 1994) doi:10.1038/368113a0 figure 1 how they treat the bead in order to get it to stick but I don't really understand it.

  3. Well, they essentially dipped them in detergent and spread them on the coverslip. Next they air-dried the slip. The surface was then coated with nitrocellulose (which is a fibrous polymer).

    So would the lipid tails attach themselves to the bead, allowing the head groups to interact with the polymer?