Exam 1 Biol 213 Molecular Cell Biology Fall 2011 Name____________________________ In drawing structures, neatness counts. The space provided for each question should be sufficient for your answers. Note that there are 102 points on this exam but the maximum score you can receive is 100. Use your time wisely. Questions 1-11 are worth 3 points each. Circle your answer(s). 1. Which of the following are NOT tenets of the cell theory? (a) Cells can only arise by division from a pre-existing cell (b) The cell is the smallest unit of life (c) All cells are complex and highly organized (d) All organisms are composed of one or more cells 2. Glycogen is composed of: (a) α-galactose (b) β-galactose (c) sucrose (d) α -glucose (e) β -glucose 3. Which type of chemical bond is characterized by the sharing of electrons between atoms? (a) Hydrogen bond (b) Ionic bond (c) Covalent bond (d) van der Waals attraction (e) Hydrophobic interactions 4. Which chemical group is found at the C-terminus of proteins? (a) Amino (b) Amide (c) Carboxyl (d) Carbonyl (e) Carbon 5. Any reaction A ⇔ B is at equilibrium when (a) [A] = [B]. (b) ΔG = 0. (c) ΔG ° = 0. (d) ΔG = ΔG °. (e) RT = 0.6166. A bacterium is suddenly expelled from a warm human intestine into the much colder world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity it enjoyed in the intestine? (a) Increase the length of the hydrocarbon tails in its membrane phospholipids. (b) Increase the proportion of unsaturated hydrocarbon tails in its membrane phospholipids. (c) Increase the proportion of hydrocarbon tails with no double bonds in its membrane phospholipids. (d) Decrease the amount of fatty acids in the membrane. 7. At first glance, it may seem that living systems are able to defy the second law of thermodynamics. However, on closer examination it becomes clear that although cells create organization from raw materials in the environment, they also contribute to disorder in the environment by releasing: (a) water (b) radiation (c) heat (d) proteins (e) ions 8. Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S → ES Keq for ES = 10 E + I → EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? (a) E binds I more tightly than S. (b) When S is present in excess, no I molecules will bind to E. (c) The binding energy of the ES interaction is greater than that of the EI interaction. (d) Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative. (e) E is more specific for I. 9. Which of the following is false? (a) Enzymes change the equilibrium of biochemical reactions. (b) An enzyme catalyzes just one or a very small number of different reactions. (c) The temperature increase required to speed up a reaction by an appreciable extent is often huge. (d) Reactions inside cells are often mediated by enzymes. (e) Enzymes can often accelerate reactions to a much greater extent than can heat. 10. Which type of interaction is responsible for α-helices and β-sheets in proteins? (a) covalent (b) hydrogen bonds (c) electrostatics (d) van der Waals (e) hydrophobic11. Which of the following statements is true? (a) Peptide bonds are the only covalent bonds that can link together two amino acids in proteins. (b) The polypeptide backbone is free to rotate about each peptide bond. (c) Nonpolar amino acids tend to be found in the interior of proteins. (d) The sequence of the atoms in the polypeptide backbone varies between different proteins. 8 points (2 points each) 12. The product Y of an enzymatic reaction absorbs light at the wavelength 260 nm and the product Z of another reaction absorbs at 340 nm, unlike the common substrate of the reactions. A spectrophotometer was used to measure the initial rate of production of Y and Z by the reactions shown below. The initial rates were measured for several independent reactions, all containing equal amounts of enzyme A or enzyme B and differing amounts of substrate X. A graph was made of the initial reaction rate (v) plotted against the concentration of X ([X]). Given the data shown, are the following statements TRUE or FALSE? ___A. Vmax(A) > Vmax(B). ___B. At [X] = 10 µM, the amounts of enzymes A and B limit the rate of reaction. ___C. KM(B) = 10 µM. ___D. If [X] = 1 µM and both enzymes are present, most of the substrate will be converted to Z rather than Y.8 points (4 points for T/F, 4 points for the correct reason(s) why an answer is false) 13. Indicate whether the following statements are true or false. If a statement is false, explain why it is false. ___A. Feedback inhibition is defined as a mechanism of down-regulating enzyme activity by the accumulation of a product earlier in the pathway. ___B. If an enzyme’s allosteric binding site is occupied, the enzyme may adopt an alternative conformation that is not optimal for catalysis. ___C. Protein phosphorylation is another way to alter the conformation of an enzyme and serves exclusively as a mechanism to increase enzyme activity. ___D. GTP binding proteins typically have GTPase activity, and the hydrolysis of GTP transforms them to the “off” conformation. 5 points 14. What is the pH of a 1 mM solution of HCl (a strong acid)? ___________ 6 points (no partial credit will be awarded) 15. Indicate below how to prepare 2 liters of a 20 mM gomless, 10 mM NaCl solution using dry gomless powder (100 g/mole), a 1 M NaCl stock solution and water. Be sure to clearly indicate units. gomless: ____________ 1 M NaCl stock: ____________ Water: ____________8 points (2 points each) 16. Fill in the building blocks for each of the macromolecules found in cells: Polysaccharides => _______________________ Proteins => _______________________ Nucleic Acids => _______________________ Fats, Lipids, Membranes => _______________________ 5 points 17. Draw the structure for glucose (α or β form) and indicate carbon 4 (C4) with an arrow. 5 points 18. You need to store milk for a very long period of time without refrigeration. Should you pasteurize or sterilize the