The nonspecific binding constant of a bacterial transcription factor for DNA has been…

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Macromolecules, membranes and cell architecture · Macromolecules, membranes and cell architecture

Forces, Machines and Signals, Ch Charges in salt water and the assembly of amphiphiles

Problem

The nonspecific binding constant

K_a

of a bacterial transcription factor for DNA has been measured at three sodium concentrations. Data:

c_{\rm salt}=50\,\mathrm{mM}

K_a=1.28\times10^{11}\,\mathrm{M^{-1}}

;

c_{\rm salt}=200\,\mathrm{mM}

K_a=2.00\times10^{9}\,\mathrm{M^{-1}}

;

c_{\rm salt}=800\,\mathrm{mM}

K_a=3.125\times10^{7}\,\mathrm{M^{-1}}

. ((a)) Translate the data into a plot of

\ln K_a

against

\ln c_{\rm salt}

and show that the three points lie on a straight line. ((b)) Read off the slope and state the number of counterions

m

released on binding. ((c)) State, with a one-sentence reason based on counterion release, whether the affinity strengthens or weakens as salt rises.

Browse the problem library