CHEM-342 INTRODUCTION TO BIOCHEMISTRY

MIDTERM EXAMINATION - PART I (individual work)

Thursday 2 April 1998

7:00 - 9:00 p. m. 208 Gore Hall

Instructor: Hal White


INSTRUCTIONS - Read them before you turn the page.

1. Sit one or two students per table.

2. This examination has two parts. Complete the questions in Part I individually and turn in your answers by 9:00. If you finish early, you may leave the room until Part II, the group part, starts at 9. Part I is worth 75 points. Part II is worth 25 points. This examination will constitute 20% of your final grade.

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

GRADING

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, and are written clearly and logically. 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. Stream of consciousness answers are rarely well organized or clearly presented.

Part I Individual work (75 points)

1. (35 points) The following short answer questions worth 5 points apiece are based on learning issues raised in different groups this semester.

A. If, as we now know, the oxidation state of iron in hemoglobin was unchanged in Stokes' experiments, then the coloring matter of blood was not being oxidized and reduced as Stokes thought. What was being reduced by SnCl2 and Fe SO4 in Stokes' experiments? Show with a chemical equation how his experiment resulted in a color change in hemoglobin.

B. In the experiment described in Stokes' Section 11, what did the water washes do to the ether phase that caused the extracted hematin to become insoluble and precipitate at the interface?

C. While careful analysis of crystalline hemoglobin shows one iron atom per ~16,800 amu regardless of the source of the hemoglobin, the ratio of iron to sulfur varies quite a bit. Show how a hemoglobin could have a stoichiometry of 2 Fe to 5 S.

D. Herrick's patient was jaundiced. Biochemically, why do people with sickle cell anemia frequently have jaundice?

E. What is dithionite? Why did Pauling and coworkers use dithionite in their electrophoresis buffers?

F. Identify the molecule shown below. What is it used for?

G. In a particular African population, 1% of all children born develop sickle cell anemia. Estimate the proportion of the children in this population who will have sickle cell trait?

Bonus Questions (2 points each)

Herrick's patient came from Grenada. Where precisely is that?

What is the Wassermann test used for?


2. (10 points) Imagine you have to evaluate a bunch of concept maps on the topic of sickle-cell anemia and need to establish some criteria to differentiate satisfactory maps from excellent maps. Make a list of important concepts that you would expect to be incorporated in an excellent map. You may annotate your list with comments on the relative importance of the concepts and the depth of understanding expected.

3. (15 points) Assume that Diggs and coworkers had a sensitive spectrophotometer that would allow them to measure the visible spectra of the blood samples they observed under the microscope.

A. Draw a representation of the spectra they would observe at 0, 6, and 24 hours for blood from a person with sickle cell trait. Explain your reasoning.

B. Would the spectrophotometer reveal any consistent difference between samples from people with sickle cell anemia, those with the trait, and normals? Please state your reasoning.

4. (15 points) Figure 1 in the article by Pauling and coworkers shows the electrophoretic mobility of carbonmonoxy-hemoglobins A and S. On that figure shown below are drawn the electrophoretic mobility of three previously uncharacterized carbonmonoxy-hemoglobins "X," "Y," and "Z."

For HbX, HbY, and HbZ:

a. describe concisely what you notice about its electrophoretic behavior, and

b. make a reasoned argument for what the observations must mean about the possible structural differences of each. Try to extract as much information from the figures without over interpreting.

Hemoglobin X.

Hemoglobin Y

Hemoglobin Z

Bonus (2 points) HbC from the electrophoresis demonstration would correspond to which above?

CHEM-342 INTRODUCTION TO BIOCHEMISTRY

MIDTERM EXAMINATION - PART II (Group work)

Instructions

Problem 4 from Part I will be answered again in Part II but with the benefit of group discussion and with access to reference books. 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. 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.

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 on Friday morning.

Have a safe and enjoyable Spring Break!

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


4. (15 points) Figure 1 in the article by Pauling and coworkers shows the electrophoretic mobility of carbonmonoxy-hemoglobins A and S. On that figure shown below are drawn the electrophoretic mobility of three previously uncharacterized carbonmonoxy-hemoglobins "X," "Y," and "Z."

For HbX, HbY, and HbZ:

a. describe concisely what you notice about its electrophoretic behavior, and

b. make a reasoned argument for what the observations must mean about the possible structural differences of each. Try to extract as much information from the figures without over interpreting.

Hemoglobin X.

Hemoglobin Y

Hemoglobin Z