Quiz 2 key (1) - (8 points List the concentrations of each...

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Biochemistry 309, Winter 2010 20 points Quiz #2 NAME: _____________________________ TA:__________________ 1. List three ways in which you can determine the abundance of an enzyme during purification. (3 points) 1. Activity 2. Absorbance at 280 nm 3. SDS PAGE 2. During the purification of an enzyme, how is the fold purification measured? (2 points) Fold purification is the ratio of the specific activity after a step to the specific activity before a step. Specific activity is defined as the activity (in units) per mg of protein. 3. Is dialysis a useful method for purifying a protein away from high molecular weight contaminants? Explain your answer. (3 points) No. Dialysis results in dilution and eventually removal of molecules below a particular molecular weight. 4. In a final volume of 1L, you combine 100ml 1M acetic acid (pKa = 4.76), 5ml 1M sodium acetate and 5ml of the strong base 1M sodium hydroxide.
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Unformatted text preview: (8 points) List the concentrations of each component: 100mM acetic acid 5mM sodium acetate 5mM sodium hydroxide List the final concentrations of each ion: 10mM Acetate 10mM Sodium What is the pH of the solution? pH = pKa + log [A-] = 4.76 + log (10mM/95mM) = 4.76 – 0.98 = 3.78 [HA] 5. Two mutations (A and B) in an enzyme reduce its affinity for its substrate. Mutant A introduces a tryptophan in place of an alanine in the substrate-binding pocket. Mutant B introduces a glycine in place of a tyrosine in a distant part of the protein. Why might each of these mutations affect substrate binding? (4 points) Mutant A: Because the tryptophan is larger than alanine, it likely makes the substrate binding site less well suited to bind the substrate. Mutant B: The glycine in place of the tyrosine might create more flexibility in the protein, causing it to bind to its substrate less well....
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