Important - Please read this before you turn the page.

• Write your name on each page

 
• This part of the midterm examination is worth 75 points distributed as follows:

            B. ( 45 points) Problem and Short Essay Questions.

• You may refer to your notes, course reader, handouts, or graded homework assignments. Textbooks or reference books cannot be used.

 
• This examination will assess your learning, problem-solving skills, and ability to communicate clearly. It is intended to be challenging even to the best students in the class. Writing reflects how you think. Among the "right answers" I will read for the following questions, some will be better than others because they show greater depth of understanding, avoid extraneous or inaccurate information, provide a more logical structure, use appropriate examples, and chose words with precision. Better quality answers will receive higher marks. Therefore organize your thoughts before you write. Strive to write not that you may be understood, but rather that you cannot possibly be misunderstood. Stream of consciousness answers are rarely well organized or clearly presented.


Have a relaxing and safe Spring Break.

A. Relation of hemoglobin to methemoglobin

B. Starch iodine test used by Zinoffsky

C. Difference between decomposition and incineration of hemoglobin.

D. A stoppered suspension of blood cells will gradually change from red to purplish.

E. The source of sulfur in hemoglobin.

F. Red blood cells sink more slowly in 2M NaCl than in blood serum.

G. Reducing agents cause a spectral change in hemoglobin yet the iron remains Fe II.

H. Blood in veins appears blue but is bright red when a person bleeds.

I. In preparing hemoglobin for iron analysis, how does Zinoffsky eliminate sulfur, nitrogen, carbon, and hydrogen from his sample?

J. Gravimetric and Manometric analysis.

Bonus question (2 Points) Draw a diagram that clearly shows how one should arrange three trapezoidal tables in 208 Gore Hall to form a table surface in the shape of an equilateral triangle.

Part II Problems and Short Essays

1. (10 Points) Professor Essigsauer is back in the lab playing around with paper chromatography this time. Having failed in his initial quick-and-dirty attempts at getting hematin to migrate using diethyl ether or distilled water as a solvent system, he has started rummaging around the lab looking for other solvents to try. Unfortunately, his impatience is getting in the way of a more systematic approach. Based on your experience and understanding:

Why didn't diethyl ether or water work as a chromatography solvent for hematin?

What solvents or solvent mixtures do you think Dr. Essigsauer should try next?

Provide a clear explanation for your recommendations.

2. (8 Points) Explain (1) why crystallization is a chemical criterion for purity and (2) why the elemental analysis of the mother liquor in Zinoffsky's study provided an additional indication that his hemoglobin crystals were pure. Feel free to use illustrations to support your explanations.

3.  (12 Points) "Progress depends on new techniques, new discoveries, and new ideas, probably in that order." Sydney Brenner Analyze each of the three articles you have studied so far this semester in the context of Brenner's quotation.

4. (15 Points) Read the following abstract from an article in The Journal of Biological Chemistry 268, 26972 (1993), and answer the questions that follow.

 

The Hemoglobins of the Bullfrog, Rana catesbeiana DEOXYGENATION-LINKED ASSOCIATION OF TETRAMERIC COMPONENTS B AND C TO FORM TRIMER BC2: SEDIMENTATION ANALYSIS AND OXYGEN EQUILIBRIA Lei-ting Tam‡, David Manning ¶, David J. Cox ¶, and Austin Riggs‡ From the ‡Department of Zoology, University of Texas, Austin, Texas 78712 and the ¶Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506 Hemolysates from the adult bullfrog, Rana catesbeiana, show an unusually high degree of cooperativity of oxygen binding with Hill coefficients greater than 4. The principal components of the tetrameric hemoglobin, B and C, do not show this high cooperativity when isolated, but it reappears when the components are mixed. Sedimentation velocity measurements show that the unusual behavior results from mixed association of components B and C to form complexes larger than tetramers. Computer simulation of the sedimentation behavior of mixtures of deoxygenated B and C components shows that the gradient profiles can be satisfactorily described in terms of an equilibrium between the B and C tetramers and a BC2 trimer. The simplest model consistent with the results is the mixed association: B + C BC and BC + C BC2, with the second binding constant being higher than the first, indicating significant cooperativity. The extent of association is highest at low pH and low temperature. The dissociation of the B•C complex with low oxygen affinity to higher affinity B and C molecules during oxygenation results in greatly increased cooperativity of oxygen binding with higher Hill coefficients than possessed by either component alone in equilibria measured between 5 and 25 C and between pH 6 and 8.

B. (3 Points) How many iron atoms would you expect in the BC₂ trimer? Why?

C. (5 Points) Sketch the oxygen binding curve for bullfrog hemoglobin B or C showing what is meant by cooperativity and indicate how it would differ from that when B and C are present together.

D. (5 points) You are not expected to fully understand the abstract. However, you are expected to be able to focus in on critical aspects that you don't understand (learning issues). In your own words, describe what you think the abstract is saying and identify two substantive learning issues that you would need to pursue to better understand the article.