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Consider a protein A, which has N monomeric units each of length a. For simplicity, treat the chain as one-dimensional: each unit can make a displacement +a (to the right) or -a (to the left) in the x direction. The end-to-end distance of the protein is x, where x=La: the chain starts at the origin and ends at x=La after N steps (thus L is the number of steps to the right minus the number of steps to the left).

What is the maximum possible value of L? What is the minimum possible value of L? How many configurations correspond to each of these values?

Calculate the entropy of the protein when its end-to-end distance is x=La (assume L>>1 and use Stirling's Approximation).

I'm totally lost. Any help would be greatly appreciated!

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What have you tried? What do you know about these things, what are you missing? What's your definition of entropy? The more context you provide, the more the answers can be tailored to what might help you. –  joriki Oct 23 '12 at 17:20
    
I'm having trouble finding a place to start...I know that the protein is being treated as a random stepping entity, but that's about it. Don't know how to set it up, how to find max/min L, etc... –  Alex Trent Oct 23 '12 at 21:06
    
Again, what's your definition of entropy? –  joriki Oct 23 '12 at 21:25

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