1. Assume you have 2 moles of an ideal gas trapped in a container at 56°C and a pressure of 1atm. Calculate ∆U, q and w if the gas is compressed
a. Reversibly and isothermally to 3atm
b. Irreversibly and isothermally to 3atm against an external pressure of 4 atm

2. Assume you have 4moles of an ideal gas at 3 atm and 33°C which is expanded through a series of isothermal steps to 1atm. Calculate q and w for all of the steps and total these for an overall q and w.
a. Step 1: gas expands to 2.5 against an external pressure of 2.5atm
b. Step 2 gas expands to 2atm against an external pressure of 2 atm
c. Step 3 pas expands to 1.5 atm against an external pressure of 1.5 atm,
d. Step 4 gas expands reversibly to 1 atm.

4. Many proteins are stabilized in the final folded form by di-sulfide linkages (covalent bonds between two cysteine residues in the sequences. One of the roles of chaperone proteins is to prevent the formation of incorrect disulfide linkages. Through this question you will appreciate why this might be an issue for cells.
a. Determine the number of different possible di-sulfide linkage in protein that has the following Cys-residues: 3, 4 and 5
b. Assume you have discovered a mammalian protein with 7 cys residues in its primary sequence. You have isolated two forms of this protein from an E. Coli expression system. One with the native configuration and one with a different fold. You determine that these two forms of the protein have different di-sulfide linkages. Can you explain this result.

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                              n = 2mole
                              Pi = 1.0 atm
                              Vi = 53.956 lit (From PV = nRT)
                              Ti = (273+56) K = 329K
          Internal energy (U) is a function of temperature, U=f(T)
If it is an isothermal process, the temperature remains constant throughout the process. Change in internal energy will be zero...

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