Download MCB100A/CHEM130A In-Section Quiz #2 (Aathavan Karunakaran)

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MCB100A/CHEM130A In-Section Quiz #2
(Aathavan K, 7th Oct 2005)
(Open Book, 15 minutes)
1. A. Rank the following in the order of increasing tolerance to mutations in a
protein: hydrophobic core, hydrophilic surface, catalytic site. Explain your
ordering briefly (atmost 2-3 sentences) (3)
Catalytic site (functionally important residues – often very very specific)
Hydrophobic core (tolerates most hydrobic residues, and polar uncharged
residues)
Hydrophilic Surface (tolerates almost all sorts of residues)
B Define Convergent Evolution (1)
When similar traits develop independently in two different species whose different
ancestors didn’t have that trait.
2. Consider Ribonuclease-A from Anfinsen’s original experiment. You have
mutated one of the cysteines into a serine (there are now only 7 cysteines), but the
mutant protein is just as active as the wild-type. You now repeat the Anfinsen
experiment on this mutant protein: i.e, unfolded the protein with urea, reduced all
the disulfide bonds, put the protein in oxidizing environment to reform disulfide
bonds, and then allowed to refold by removing the Urea). What percent of the
original activity would you expect to recover. (6).
Note: Consider in this experiment, like in the original one, only intra-molecular
disulfide bonds are formed but not inter-molecular bonds. Clearly show the logic
of your calculation.
You can form only 3 disulfide bonds. And the number of ways of doing this is
7.6.5.4.3.2.
------------ = 105
3! 23
So activity recovered = 100/105 = 0.95% which is the same as the case with 8
cystines