Category Archives: Biophysics

Receptor # Threshold for Cell-Cell Adhesion

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How do two cells that can adhere, decide whether or not they should adhere? Typically, potentially adherent cells become adherent by increasing their adherence-receptor expression levels (R1/R2) past a certain “threshold” or “EC50” (see figure above). A classic 1984 paper defined this EC50 as a function of R1/R2‘s binding constant Ksoln as illustrated above for two average eukaryotic cells.1,2 This equilibrium model for cellular adhesion is described in more detail below.

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Timescales, Kinetics, Rates, Half-lives in Biology

Understanding interactions between processes with different rates can made significantly easier when you know the approximate timescales or half-lives for those processes.   Comparing two processes (e.g. alpha helix folding of a peptide chain (micro seconds (10-6s)) and translation of a peptide chain ( milliseconds(10-3s))) if the timescales differ by more than a factor of 100 then you can reasonably assume that as the faster process is occurring, the slower process is standing still (i.e. not occurring). Equivalently you can assume that as the slower process is occuring the faster process occurs instantly. What this means for the example cited above is that the folding of a peptide chain can and does occur before translation of that peptide chain has finished.1-3

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