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UD CHEM 342 - Midterm Examination - Individual Part

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CHEM-342 Introduction to Biochemistry Name ______________________________ Midterm Examination - Individual Part Wednesday, 26 March 2008 H. B. White - Instructor Important - Please read this before you turn the page. There are 9 pages to this examination including this page and the blank final page. Write your name on every page. This individual part of the midterm examination is worth 99 points with 7 bonus points possible. There are 11 questions of which you need to answer 7. You may refer to your notes, course reader, handouts, or graded homework assignments. Textbooks and 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. Better quality answers will receive higher marks. Therefore organize your thoughts before you write and draw. Among the “right answers” I will read for the following questions, some will be better than others because they $ show greater depth of understanding, $ provide a more logical structure, $ use appropriate examples, $ include appropriate illustrations, $ avoid extraneous or inaccurate information, and $ choose words with precision. 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.CHEM-342 Introduction to Biochemistry Name__________________________________________ Midterm Examination – Individual Part 26 March 2008 Page 2 1. (15 Points) Stokes observed the changes on the color of blood extracts after various treatments to deduce changes that had occurred. Based on your understanding of hemoglobin and its reactions described by Stokes and in class, predict the color changes expected when each of the following is done to a freshly drawn sample of blood to which citrate or heparin was included. Red Purple Brown Basis for prediction (1) Freshly drawn blood sample X Oxyhemoglobin in blood is red Seal and store solution 1 for several hours. Add equal volume of ether to solution 1. Add K3Fe(CN)6 to solution 1. Add HCl to solution 1. Add CO to solution 1. Add Na2S2O4 (dithionite) to solution 1. a. (6 pts) In the empty boxes above, put an “X” in the column that corresponds to the color you predict would result from the indicated treatment. b. (9 pts) In the empty boxes in the last column, write the basis for each prediction. c. (2 bonus points) What is the purpose of drawing blood in the presence of citrate or heparin?CHEM-342 Introduction to Biochemistry Name__________________________________________ Midterm Examination – Individual Part 26 March 2008 Page 3 2. (15 Points) The following two questions relate to the Zinoffsky (1886) article. a. (8 pts) Zinoffsky initially took extra time and effort to separate red blood cells from blood plasma, but later he simply avoided the 2% NaCl wash, added back distilled water, and proceeded to the first alcohol crystallization step. Based on Zinoffsky’s comments, draw and label two graphs in the space below, one that represents the solubility of hemoglobin (Hb) and one that represents the solubility of serum proteins as a function of ethanol concentration in water. b. (7 pts) Knowing what we do about hemoglobin now, it would be quite unlikely for the sulfur-iron stoichiometry for hemoglobin to be 1:4. Explain why this is so in words and illustrate with a drawing.CHEM-342 Introduction to Biochemistry Name__________________________________________ Midterm Examination – Individual Part 26 March 2008 Page 4 If you feel you cannot answer one of the following three 15-point questions relating to the jigsaw articles, consider Question #6 worth 10 points to substitute for question 3, 4, or 5. 3. (15 Points) The following two questions refer to the Digg et al (1933) and the Herrick (1910) articles. a. (8 points) Although they didn’t know it, Diggs and coworkers estimated the genetic frequency of the sickle gene in the US black population. At that time, they and others did not appreciate the genetic relationship between sickle cell anemia and sickle cell trait. Had they known that, they could have applied the Hardy-Weinberg Law to their data and estimated the frequency of sickle cell anemia from the frequency of sickle cell trait. The Hardy-Weinberg Equation predicts the frequency of different genotypes based on allele frequencies and has the form (p + q)2 = p2 +2pq + q2, for two alleles. This relationship can be displayed visually as a Punnet Square in which each side has length p + q, and the areas within the square correspond to each term in the expanded equation. In parts of Africa the frequency of the sickle cell gene can be as high as 40%. Fill in and label the diagram below. For such a population, identify the area in the diagram that would represent people with sickle cell anemia. Estimate the percentage of the population that would suffer from sickle cell sickle cell disease. b. (7 points) Herrick noted that his patient had a “tinge of yellow in the sclerae” and the urine “had a trace of bile.” These related observations have significance in relation to the biochemistry of sickle cell disease. What is the connection between the sickle cell phenomenon and these clinical symptoms?CHEM-342 Introduction to Biochemistry Name__________________________________________ Midterm Examination – Individual Part 26 March 2008 Page 5 4. (15 points) Figure 7 from the Svedberg and Fåhraeus (1926) article is reproduced five times below. If conditions in the ultracentrifuge or the properties of hemoglobin were different, the concentration profile in Figure 7 might have been different. This question asks you to sketch in the concentration profile expected for five different hypothetical situations. In all cases except “e”, the initial hemoglobin concentration in mg/ml is the same. Each answer is worth 3 points. a. Human CO hemoglobin rather than horse CO hemoglobin was used. b. The angular velocity, ω, of the centrifuge was doubled. c. The solvent was 10% ethanol in water


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