Exam 2 Biol 213 Molecular Cell Biology Fall 2011 Name________________________________ The space provided for each question should be sufficient for your answers. Note that there are 105 points on this exam but the maximum score you can receive is 100. Use your time wisely. Questions 1-14 are worth 3 points each. Circle your answer. 1. Based on our discussion in class, which is the first committed step in glycolysis: (a) aldolase (b) hexokinase (c) crytochrome oxidase (d) phosphofructokinase (e) pyruvate kinase 2. What is the net yield of ATP from one molecule of glucose during glycolysis? (a) 0 ATP (b) 1 ATP (c) 2 ATP (d) ~30 ATP (e) none of the above 3. Which of the following would be required to move glucose against its concentration gradient? (a) a glucose channel (b) facilitated diffusion through a glucose transporter (c) a Na+ channel (d) a glucose symporter (e) simple diffusion across a membrane 4. The final product of the Calvin cycle is ______. (a) water (b) oxygen (c) ribulose 1,5-bisphosphate (d) glyceraldehyde 3-phosphate (e) glucose 5. Which of the following statements about mitochondria is FALSE? (a) Protons are pumped from the matrix into the intermembrane space. (b) ATP is synthesized in the intermembrane space. (c) Mitochondria contain DNA. (d) The outer membrane is permeable to protons. (e) The inner membrane is folded into cristae.6. Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? (a) by closing Na+ channels (b) by preventing the secretion of excitatory neurotransmitters (c) by opening K+ channels (d) by opening Cl– channels 7. Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? (a) Some channels remain closed and some open completely. (b) All channels open completely. (c) All channels open partly, to the same degree. (d) All channels open partly, each to a different degree. 8. Which of the following statements about the carbohydrate coating of the cell surface is false? (a) It is not usually found on the cytosolic side of the membrane. (b) It can play a role in cell–cell adhesion. (c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain. (d) Specific oligosaccharides can be involved in cell–cell recognition. 9. Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in the figure below. For which of these phospholipids does a flippase probably exist? (a) X only (b) Z only (c) X and Y (d) Y and Z 10. The final metabolite produced by glycolysis is ___________. (a) acetyl CoA (b) pyruvate (c) 3-phosphoglycerate (d) glyceraldehyde 3-phosphate (e) carbon dioxide X X X Y X Y Y Y X Y X YZZYZ ZZYZZYYYextracellular spacecytosol11. The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is _________ (a) more free energy is released for a given amount of glucose oxidized. (b) no energy is lost as heat. (c) energy can be extracted in usable amounts. (d) more CO2 is produced for a given amount of glucose oxidized. (e) less O2 is required for a given amount of glucose oxidized. 12. In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe? (a) The ratio of ATP to ADP in the cytoplasm would fall. (b) NADH would build up. (c) Carbon dioxide production would cease. (d) The consumption of oxygen would fall. 13. The action potential is a wave of ____ that rapidly spreads along the neuronal plasma membrane (a) sodium ions (b) neurotransmitters (c) hyperpolarization (d) electrochemical gradient (e) depolarization 14. Stage 1 of oxidative phosphorylation requires the movement of electrons along the electron-transport chain coupled to the pumping of protons into the intermembrane space. What is the final result of these electron transfers? (a) OH- is oxidized to O2. (b) Pyruvate is oxidized to CO2. (c) O2 is reduced to H2O. (d) H- is converted to H2. (e) O2 is converted to CO2. 5 points (1 pt each) 15. Circle the molecule in each pair that is more likely to diffuse through the lipid bilayer. A. amino acids or benzene B. Cl– or ethanol C. glycerol or RNA D. H2O or O2 E. adenosine or ATP6 points (no partial credit will be awarded) 16. Indicate below how to prepare 3 liters of a 100 mM gomless, solution at pH 3.0 using using dry gomless powder (100 g/mole), a 1 M HCl (strong acid) stock solution and water. Be sure to clearly indicate units. gomless: _________________ 1 M HCl stock: _________________ Water: __________________ 10 points (5 points each part) 17. Your friend isolated a new microbial species that can grow at neutral pH using either ethanol (CH3CH2OH) or acetate (CH3COO–) as the sole carbon source. She measured the rate of uptake as a function of concentration of each carbon source and obtained the following graphs: A. Which molecule (A or B) is more likely to utilize a carrier protein to mediate its transport? Why? B. Given what you know about membrane permeability and transport, is molecule A more likely to be ethanol or acetate? Why?4 points (2 points for each organelle) 18. Mitochondria and chloroplasts both have electron transport systems. For each organelle, name the molecule that serves as the terminal electron acceptor. Mitochondrial terminal electron acceptor: ________________________________ Chloroplast terminal electron acceptor: _______________________________ 12 points (2 points for each enzyme) 19. For each of the enzymes listed below, name its cellular location (which compartment, membrane etc.). Assume all refer to eukaryotic organisms. Rubisco (CO2 + ribulose 1,5-bisphosphate → 2x