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There are either two monomers A and B or one complex, AB, in equilibrium in a vo

ID: 958806 • Letter: T

Question

There are either two monomers A and B or one complex, AB, in equilibrium in a volume consisting of 106 boxes. Suppose that the interaction energy of proteins A and B in the dimer is –5 kBT. In other words, the molecular interactions that occur in the complex reduce the energy of AB by 5 times thermal energy in comparison to having two separated and non-interacting monomers.

Write the canonical partition function (considering only configurational microstates) and calculate its value.

Hint: There are two energy macrostates, the dimerAB, whose e?nergy we can take to be 0, and the separated monomers, A + B, whose energy we can take to be +5 kBT. Use the formula for the canonical partition function that states:

where W(0) is the number of microstates for the dimer, and W(5kBT) is the number of microstate for the separated monomers.

E/kBT

Explanation / Answer

number of microstates for dimer , W(0) = 1

number of microstate for the separated monomers, W(5kBT) = 3

Q = 1e-0 + 3e-5

Q = 1.020