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Biological Polymers


We studied two key biological polymers: actin and microtubules (MT). This was done using both bulk and single molecule techniques.


Microtubule Polymerization

Rhodamine-labelled tubulin was polymerized at different monomer concentrations. The current state of polymerization can be preserved in a two step process: the molecule Taxol is added to prevent depolymerization, and the solution is quickly diluted reducing the tubulin monomer concentration and hence preventing further polymerization. In this way snapshots of the reaction can be obtained under the microscope.

The students wrote Matlab code to analyze the distribution of filament lengths. By stopping the reaction at different time points information about the kinetics of polymerization can be obtained.


Actin Polymerization

Similar to the beta-galactosidase assay (The Rate of Things), students used kinetic spectrophotmetry to watch the bulk polymerization of actin filaments and deduce the monomer association rate. Pyrene-labelled actin becomes fluorescent only upon polymerization; this gives a direct readout of the amount of actin in the filamentous form. The polymerization rate can be studied at different concentrations of monomer or in the presence of protein factors like Arp2/3. As with beta-gal, the polymerization is a linear kinetic process.

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