CHEM-342 INTRODUCTION TO BIOCHEMISTRY ___________________________

MIDTERM EXAMINATION - PART I (individual work) Your Name

Thursday 25 March 1999

7:00 - 8:45 p. m. 208 Gore Hall

Instructor: Hal White

INSTRUCTIONS - Read them before you turn the page.

1. Sit with no more than two students per table.

2. This examination has two parts. Complete the questions in Part I individually and turn in your answers by 8:45. If you finish early, you may leave the room until Part II, the group part, which starts at 8:45. Part I is worth 75 points. Part II is worth 25 points. This examination will constitute 25% of your final grade.

3. You may refer to your notes, the course reader, handouts, and any homework assignments for Part I. Internet printouts, textbooks, or other reference books are permitted for Part II of this examination, but not for Part I.

4. Write your name at the top of each page.


While for some questions there is no single "right answer," some answers will be better than others. I will award better grades to answers that show a greater depth of understanding, use appropriate examples from the readings and your experience, and are well thought out and clearly written. I will be looking for high quality answers. Remember: Strive to write not that you may be understood, but rather that you cannot possibly be misunderstood. This means to use words with precise meanings and to qualify statements to reflect any uncertainty. Incorrect or superfluous information will decrease the quality of your answer. Stream of consciousness answers are rarely well organized or clearly presented.


Part I Individual work (75 points)

1. (28 points) The following seven short answer questions, worth 4 points apiece, are based on learning issues raised in different groups this semester.

A. If a starch-iodide solution turns blue, what does it indicate?

B. Why did carbon dioxide (carbonic acid) behave like a reducing agent in Stokes' experiment?

C. How is manometry put to use in studying hemoglobin?

D. Why doesn't hematin extract into an ether phase when hemoglobin is denatured with concentrated HCl rather than glacial acetic acid?

E. In a titration of FeII using a solution of KMnO4, how would you recognize the end point?

F. What is the major evidence that Zinoffsky provided to convince a reader that his hemoglobin samples were pure?

G. What is partial specific volume?


2. (10 points) Things familiar often pass without a second thought. Most likely you have observed the change in color of a beef steak upon being cooked. Postulate a biochemical explanation for how cooking might cause that change. Be specific and use examples to bolster your position.

3. A. (4 points) Draw an example of a small molecule that exhibits C2 point group symmetry.

B. (8 points) Given that we now know from the work of Svedberg and Fåhraeus that hemoglobin is four times larger than Zinoffsky thought and that X-ray crystallography shows the hemoglobin molecule to possess C2 point group symmetry, what should the iron to sulfur proportions be in the empirical formula for horse hemoglobin? Answers without an explanation will not receive credit.


4. (15 points) Carbon monoxide is deadly because it can bind to hemoglobin and competitively displace oxygen. Gustav Mann wrote on page 498 of his book, "Chemistry of the Proteids" in 1906,

Identification [of carbonmonoxyhemoglobin] by the spectroscope is not easy, as the absorption bands closely resemble those of oxyhemoglobin, but two methods allow of its ready recognition, namely: firstly, the addition of ammonium sulfide or Stokes' reagent [Ferrous tartrate] which produces no change, while in the case of oxyhemoglobin they convert the later into reduced hemoglobin with its characteristic spectrum.....

Why isn't carbonmonoxyhemoglobin converted to "reduced hemoglobin" by reducing agents? And, how is this consistent with the fact that a Caucasian poisoned by carbon monoxide retains a rosy pink complexion?


5. (10 Points) The following are the first two paragraphs of an article published in 1936.






Communicated March 19, 1936

Over ninety years ago, on November 8, 1845, Michael Faraday investigated the magnetic properties of dried blood and made a note "Must try recent fluid blood." If he had determined the magnetic susceptibilities of arterial and venous blood, he would have found them to differ by a large amount (as much as twenty percent for the completely oxygenated and completely deoxygenated blood); this discovery without doubt would have excited much interest and would have influenced appreciably the course of research on blood and hemoglobin.(1)

Continuing our investigations of the magnetic properties and structure of hemoglobin and related substance,(2) we have found oxyhemoglobin and carbonmonoxyhemoglobin to contain no unpaired electrons, and ferrohemoglobin (hemoglobin itself) to contain four unpaired electrons per heme. The description of our experiments and the interpretation and discussion of the results are given below.

1. A. Gamgee, Proc. Roy. Soc. London, 68, 503-512 (1901), and one or two more recent investigators have reported blood to be about as diamagnetic as water, without discovering the difference between arterial and venous blood.

2. L. Pauling and C. D. Coryell, These PROCEEDINGS, 22, 159 (1936).

Based on this introduction and your knowledge and understanding of hemoglobin, come up with five probing learning issues that would prepare you for reading and understanding the rest of the article.



Thursday 25 March 1999

8:45 p. m. 208 Gore Hall

Instructor: Hal White


1. You may use any resources you have brought to the examination as well as any of the reference books in the course library. The objective of the group part of the examination is to discuss the problems and come to consensus. Provided agreement is reached, each group will hand in a single answer to be graded. That grade will be added to your score on Part I.

2. If you do not agree with your group's answer, you may hand in a separate answer which will be graded and used in place of your group's grade.

3. This part of the examination should end around 10:00 p. m. Any group or individual can stay longer, within reason. Class will not meet tomorrow morning

Have a safe and enjoyable Spring Break

Please sign your names to the copy that you turn in.

Group Number _____ Group Members ____________________________________





6. (25 points) Figure 7 in the article by Svedberg and Fåhraeus shows the concentration of carbonmonoxyhemoglobin as a function of distance from the center of rotation. (Note there is a misprint. From the data in Table I.2, the values should be 4.76 cm and 4.26 cm, rather than 4.21. Each data point is separated from its neighbor by 0.05 cm.)

Qualitatively depict (draw a line for) how the hemoglobin concentration profile would change in Figure 7 for each of the following cases. For full credit you need to explain your reasoning.

i. The rotational velocity was decreased by 50%.

ii. The molecular weight of hemoglobin was actually 16,700.

iii. The partial specific volume of hemoglobin was very close to that of water.

iv. The temperature was decreased by 10 degrees C.

v. Methemoglobin was used in place of carbonmonoxyhemoglobin.

vi. The initial concentration was doubled.

vii. Hemoglobin was involved in a dynamic aggregation-disaggregation equilibrium involving monomers, dimers, and tetramers.

viii. UV light around 280 nm rather thamn visible light was used to determine protein concentration.