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Q3 - STUDENT ID KEY A BIOBM331 QUIZ 3a 1(8 pts Calculate...

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STUDENT ID __ KEY A ___ BIOBM331 QUIZ 3a 9/20/06 1. (8 pts) Calculate the magnitude of the free energy change by which prolyl isomerase lowers the barrier for peptide cis/trans isomerization, given that: (RATE cat / RATE uncat ) = (exp - G o ± /RT ) cat / (exp - G o ± /RT ) uncat R = 0.00832kJ/mol x K and T = 300K G o RATE cat /RATE uncat = 2500. 2500 = e - ( Go/RT) ln(2500) = - ( Go/RT) 7.8 = - ( Go)/2.5kJ/mol ( Go) = 20 kJ/mol 2. (8 pts) Use the diagram to the right to describe the protein ribonuclease (RNase). Three different conditions occur. Draw directly on the diagram the appropriate plot for RNase. Label plots as a, b, and c. Label "N" for native structure on the structural coordinates axis. a. Physiological conditions b . In 8M urea plus HO-CH 2 CH 2 SH c . After condition (b, above), followed by extensive dialysis, then air oxidation. Full enzymatic activity is recovered by this procedure. d. Procedure (c) takes 10 hours. But in a cell, folding takes 2 minutes. Check the one reason for this time difference: In a cell, proteins are "crowded", speeding the folding In (c), proteins are "crowded", slowing the folding In a cell, enzymes speed up the Φ,Ψ rotations In a cell, an enzyme speeds disulfide interchange 3. (6 pts) Consider G = H - T S for the “reaction” PROTEIN unfolded PROTEIN folded Circle T if true, F if false: T/F The entropy of the protein, not considering the water, is much lower in the folded state. T/F The entropy of the water is much lower when the protein has folded. T/F Of all the interactions driving a water-soluble protein to fold, the hydrophobic interaction is the most important. T/F Formation of the large number of hydrogen bonds is very important in driving a protein to fold. T/F The hydrophobic interaction becomes larger and larger the higher the temperature, in the range 0 - 40 o C.

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Q3 - STUDENT ID KEY A BIOBM331 QUIZ 3a 1(8 pts Calculate...

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