Bio301 Biochemistry
Optional make-up exam, January 19, 2004
Question 1.(10 points) Why is an a-helix the preferred structure for transmembrane
protein segments? (10 points)
Question 2. (10 points) An understanding of the structure and function of membrane
proteins has lagged behind that of other proteins. The primary reason is that
membrane proteins are more difficult to purify and crystallize. Why might this be the
case?
Question 3. (10 points) Fill in the blanks:
a) Solubilizing a protein by increasing the ionic strength of a solution is
termed........................ Precipitating a protein at high ionic strength is
termed..................
b) ..................... , .............................. and ........................ bonds are important in
substrate binding.
c) DEAE-cellulose is a(n) ............................exchanger. CM-cellulose is a(n)
............................ exchanger.
d) Two general classes of enzymatic catalysis are .............................................
and .......................... .
e) A protein with a net negative charge will bind strongly to an anion-exchange
resin. A buffer, with a..............................pH or ............................... ionic
strength than the original bufer will be needed to elute such a protein.
Question 4. (15 points) What is the free-energy cost of pumping Ca+2 out of a cell
when cytosolic concentration is 0.4 M, the extracellular concentration is 1.5 mM and
the membrane potential is –60 mV?
Question 5. (10 points) Trypsin, chymotrypsin, and carboxypeptidase A fail to cleave
peptide bonds involving proline. Trypsin, for example, will not cleave a peptide at a
Lys-Pro junction. Why do you think this is the case?
Question 6. (10 points) After examining the structural formulas of the four lipids
below, answer the following questions:
a) Which are phosphoglycerides?
b) Which is a glycolipid?
c) Which contain sphingosine?
d) Which contain choline?
e) Which contain glycerol?
Question 7. (20 points) List the four major regulatory mechanisms that control
enzyme activity and give examples of each.
Question 8 (15 points) : From the data below for a hypothetical enzyme-catalyzed
reaction, determine KM and Vmax by inspection. Then plot the data using the EadieHofstee method and determine these constants graphically. Check your results with a
calculation. Can you explain the discrepancy in your two determinations?
[S] (moles/liter) v(moles/min)
5.0 x 10-4
125
2.0 x 10-4
125
6.0 x 10-5
121
4.0 x 10-5
111
3.0 x 10-5
96.5
2.0 x 10-5
62.5
1.6 x 10-5
42.7
1.0 x 10-5
13.9
8.0 x 10-6
7.50