Midterm Exam I QA

Midterm Exam I QA - Bio115 Midterm Exam I (1st of May,...

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Bio115 Midterm Exam I (1 st of May, 2007) Number in brackets indicates the maximum number of points given for the answer. Q. 1 (2) How many meters are 1 Angstrom? A. 1 1 Angstrom = 10 -10 m. Q. 2 (4) Catalysts speed up the rates of chemical reactions. a. Describe catalysis in thermodynamic terms. b. To which class of molecules belong almost all biological catalysts? c. What is the biological function of enzyme catalysis? d. What determines the catalytic specificity of enzymes? A. 2 a. A catalyst lowers the (free) activation energy. b. Proteins. c. The biological function of enzyme catalysis is the selection of chemical reactions. d. The enzyme’s amino acid sequence determines its catalytic specificity. Q. 3 (2) In 1864 Felix Hoppe-Seyler reported the crystallization of a protein, hemoglobin. What was the implication of this finding? A. 3 Proteins have precisely defined structures. Q. 4 (2) Determine the net charge carried by the side chains of the following peptide (for simplicity assume that carboxyl and amino groups are fully charged): ILDLQLACEDNSGLPEESQFQTWLNAVI. A. 4 Count the Ds and Es and subtract the number of Rs and Ks. The result is -5. Q. 5 (4) Linus Pauling showed that sickle cell anemia is a genetically inheritable trait that affects hemoglobin. Describe the experimental approach that Vernon Ingram used to demonstrate that the affected gene of sickle cell anemia patients corresponds to a hemoglobin with altered amino acid sequence. A. 5 Ingram analyzed trypsin fragments of wild type and sickle cell anemia hemoglobin by electrophoresis and chromatography to show that one fragment was altered in charge. Determination of the peptide’s amino acid sequence revealed that WT and sickle cell anemia hemoglobin differ in one amino acid. Q. 6 (4)
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Pauling and Corey suggested that DNA is composed of three rather than two nucleotide strands wound about each other. a. Which structural feature of DNA, derived from the X-ray data of R. Franklin, precluded this possibility? b. Which implication had this structural feature with respect to the orientation of the two nucleotide strands in the DNA? A. 6 a. The sugar-phosphate backbone of DNA has dyad symmetry about the axis perpendicular to the long axis of the DNA. A three stand configuration precludes such symmetry. b. The two strands had to be antiparallel. Q. 7 (3) Indicate in Angstrom the diameter, the helical rise, and the helical repeat distance of B form DNA. A. 7 20, 3.4 and 34, respectively. Q. 8 (4) Name two differences and two similarities between B DNA and A DNA? A. 8 The ribose conformation in B DNA is C2’ endo, and C3’ endo in A DNA. This conformation leads to a larger rise per base pair in B DNA when compared to A DNA. Both DNAs are left-handed double helices. The bases are in anti position in both DNA
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Midterm Exam I QA - Bio115 Midterm Exam I (1st of May,...

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