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BCH401G exam 1
Fall 1997
Name: __________________________________________________
Also write your name on the back of the exam.
Read each question thoroughly. Most questions have multiple parts. Answer each question with as complete and
precise an answer as possible. Do not include extraneous information that does not answer the question (in some cases
you may be graded lower for including irrelevant information, whether it is true or not).
1.
(20 pts) The pH of a 0.01 M monobasic acid is 2. Is this a weak acid or a strong acid? Why?
You are given a 10 mM aqueous solution of HCl. What is [H+], [Cl-], and [HCl]?
Now you are given a 10 mM aqueous solution of a monobasic weak acid. You know that 10% of it dissociates in water.
What is the concentration of the hydrogen ion, conjugate base, and undissociated acid? What is the pH? What is the Ka of
the acid? (You don't need to do the calculation, but set up your answer so that it is "calculator" ready.)
2.
(16 pts) The pKa of the cysteine side chain is 8.4. Is the cysteine side chain an acid or a base? What is the chemical
name for the functional group that makes up cysteine's side chain. Draw this amino acid in the predominant forms it
would be in at pH 6 and at pH 9.5 (the other pKa's are 1.9 and 10.7). (Your drawing only needs to convey the "essence"
of the cysteine structure as we discussed in class.)
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BCH401G exam 1
Fall 1997
3.
(16 pts) Draw Val-Gln in the trans and cis configurations.
4.
(16 pts) Why do most mutations that interfere with protein function commonly affect hydrophobic residues?
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BCH401G exam 1
5.
Fall 1997
(16 pts) Normal hemoglobin has an oxygen dissociation constant of 26. A patient was brought to you whose hemoglobin
had an oxygen dissociation constant of 50. Further investigation showed that the Hill coefficient for this patient's
hemoglobin was equal to 1. Does this patient's hemoglobin bind oxygen with higher or lower affinity than a normal
individual's? Draw a graph of fractional hemoglobin saturation vs oxygen partial pressure, showing the curves for both
the normal and abnormal hemoglobins. On the graph indicate the position of the K D for the normal and the patient's
hemoglobin.
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BCH401G exam 1
6.
Fall 1997
(16 pts) You ran a mixture of proteins over a gel filtration column and collected 6 fractions. Each of the fractions were
loaded onto separate lanes of an SDS-PAGE gel in the same sequential order as the fractions came off the column.
Unfortunately, at some point during the post-electrophoresis processing of the gel, you got confused as to which side of
the gel is the original left side and which side was the original right side, so you don't know which side of the gel had
column fraction 1 and which had column fraction 6. After looking at the stained gel below, it became obvious which
side was which. Label each of the wells with a number (1-6) corresponding to what fractions they must have been.
Using the theory behind gel filtration and SDS-PAGE, explain why you made the lane assignments that you made.
You notice that in one of the lanes there appears to be a band that seems out of place (labelled "a"). Propose a reasonable
explanation for why this band appears where it does.
a
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