Cell Biology Exam 1 (Essential Cell Biology, 3rd Edition, by Alberts)

Introduction to Cell Biology Name: September 30, 2010 Student ID: Exam I - Version 1 Section 1: True and False (3 points each). 1. A virus is a living organism. A) True B) False 2. The cytoskeleton is made up of actin filaments, microtubules, and intermediate filaments. A) True B) False 3. Noncovalent bonds are too weak to influence the three dimensional structure of macromolecules. A) True B) False 4. The chemical properties of amino acid side chains include charged, uncharged polar, and nonpolar. A) True B) False 5. The mitochondria use molecular oxygen to produce H2O and ATP. A) True B) False 6. During the first three steps of glycolysis, the cell must use one molecule of ATP before an intermediate (fructose-1,6-bisphosphate) is created that eventually yields energy. A) True B) False 7. When subjected to anaerobic conditions, glycolysis in mammalian cells continues and causes a buildup of pyruvate in the cytosol. A) True B) False 8. Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them. A) True B) False 9. Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell. A) True B) False 10. The hydrophobic forces that hold a membrane together are essentially identical to the hydrophobic forces that drive protein folding. A) True B) False 1 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 11. Phosphatidylserine is the most abundant type of phospholipid found in cell membranes. A) True B) False 12. The “polypeptide backbone” refers to all atoms in a polypeptide chain, except for those that form the peptide bonds. A) True B) False Section 2: Multiple Choice. Identify the single BEST answer for each question (3 points each). 13. The flow of genetic information is controlled by a series of biochemical reactions that result in the production of proteins, each with its own specific order of amino acids. Choose the correct series biochemical reactions from the options presented here. A) replication, transcription, translation B) replication, translation, transcription C) translation, transcription, replication D) translation, replication, transcription 14. By definition, procaryotic cells do not possess . A) a nucleus B) replication machinery C) ribosomes D) membrane bilayers 15. Which of the following organelles has both an outer and an inner membrane? A) endoplasmic reticulum B) mitochondrion C) lysosome D) peroxisome 16. Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. Some have ? helices, some have ? sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements? A) specific amino acid sequences B) side-chain interactions C) the hydrophobic core interactions D) hydrogen bonds along the protein backbone E) none of the above 2 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 17. The biosynthetic pathway for the two amino acids E and H is shown schematically in the Figure below. You are able to show that E inhibits enzyme V, and H inhibits enzyme X. Enzyme T is most likely to be subject to feedback inhibition by alone. A) H B) B C) C D) E E) A 18. The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells? A) a change that prevents Ras from being made B) a change that increases the affinity of Ras for GDP C) a change that decreases the affinity of Ras for GTP D) a change that decreases the rate of hydrolysis of GTP by Ras E) none of the above 19. Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufficient to ensure the unidirectional movement of a motor protein along its substrate? A) A conformational change is coupled to the release of a phosphate (Pi). B) The substrate on which the motor moves has a conformational polarity. C) A conformational change is coupled to the binding of ADP. D) A conformational change is linked to ATP hydrolysis. 20. Which of the following membrane lipids does not contain a fatty acid tail? A) Phosphatidylcholine B) A glycolipid C) Phosphatidylserine D) Cholesterol 21. A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity? A) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds. B) Produce lipids with hydrocarbon tails that are shorter and have more double bonds. C) Increase the amount of cholesterol in the membrane. D) Decrease the amount of glycolipids in the membrane. 3 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 22. Which of the following statements is true? A) Phospholipids will spontaneously form liposomes in nonpolar solvents. B) In eucaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer. C) Membrane lipids diffuse within the plane of the membrane. D) Membrane lipids frequently flip-flop between one monolayer and the other. 23. Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol? A) membrane permeability B) membrane fluidity C) membrane rigidity D) membrane thickness 24. Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks? A) flippases B) phospholipases C) convertases D) glycosylases 25. We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin. This protein uses sunlight as the source of energy to pump out of the cell. A) ATP B) H+ C) K+ D) Na+ 26. Plasma membranes are extremely thin and fragile, requiring an extensive support network of fibrous proteins. This network is called the . A) cortex B) attachment complex C) cytoskeleton D) spectrin 4 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 27. Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure A. Which type of defect described below is the most likely to cause the redistribution of that protein around the entire cell, shown in Figure B? A) a nonfunctional protein glycosylase B) the deletion of a junctional protein C) the truncation of a protein found in the extracellular matrix D) a nonfunctional flippase 28. The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular that is presented on the surface of a target cell. A) oligosaccharide B) aminophospholipid C) polysaccharide D) sphingolipid 29. We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? A) SDS B) SPT C) GFP D) FRAP 30. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)? A) 24 carbons with 1 double bond B) 15 carbons with 2 double bonds C) 20 carbons with 2 double bonds D) 16 carbons with no double bonds  5 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 31. When glucose is transported from the lumen of the gut through a gut epithelial cell, what form of transport is occurring at the apical surface of the cell? A) Glucose driven sodium symport B) Sodium driven glucose symport C) Passive transport of glucose D) Sodium driven glucose antiport E) None of the above 32. What happens immediately after the sodium (Na+) potassium (K+) pump hydrolyzes ATP? A) Sodium is bound. B) ADP is bound. C) The pump is phosphorylated. D) The pump changes conformation. E) Potassium is released. 33. What prevents the action potential that is moving down an axon from returning to the cell body? A) There are insulatory barriers called the nodes of ranvier that prevent backwards propagation. B) The concentration of ions is not sufficient to cause a backward flow up the gradient. C) An inactive state of the sodium channel prevents the backward flow of the action potential. D) Two of the above E) none of the above 34. Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion? A) HCO3– B) Cl– C) PO43– D) OH– 35. A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ Æ 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell’s demise? A) toxic buildup of carbon dioxide inside the cell B) toxic buildup of ethanol inside the cell C) diffusion of ATP out of the cell D) inability to import sugar into the cell 6 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 36. Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called . A) active transport B) free diffusion C) facilitated diffusion D) passive transport E) none of the above 37. Ca2+ pumps in the plasma membrane and endoplasmic reticulum are important for . A) maintaining osmotic balance B) preventing Ca2+ from altering the activity of molecules in the cytosol C) providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary for their catalytic activity D) maintaining a negative membrane potential E) none of the above 38. The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use? A) voltage-gated B) extracellular ligand-gated C) intracellular ligand-gated D) stress-gated E) none of the above 39. Which of the following is required for the secretion of neurotransmitters in response to an action potential? A) neurotransmitter receptors B) Na+-K+ pumps C) voltage-gated K+ channels D) voltage-gated Ca2+ channels E) None of the above 40. 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 41. The final metabolite produced by glycolysis is . A) acetyl CoA B) pyruvate C) 3-phosphoglycerate D) glyceraldehyde 3-phosphate 7 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 42. Glycolysis generates more stored energy than it expends. What is the net number of activated carrier molecules produced in this process (number and type of molecules produced minus the number of those molecules used as input)? A) 6 ATP, 2 NADH B) 4 ATP, 4 NADH C) 2 ATP, 2 NADH D) 4 ATP, 2 NADH 43. 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 that 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 44. Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? A) the digestion of starch to glucose B) glycolysis C) the citric acid cycle D) oxidative phosphorylation 45. Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? A) breakdown of glycogen B) glycolysis C) conversion of pyruvate to acetyl CoA D) oxidative phosphorylation 46. Which of the following processes do not take place in the mitochondria? A) citric acid cycle B) conversion of pyruvate to activated acetyl groups C) oxidation of fatty acids to acetyl CoA D) glycogen breakdown 47. The reaction cycle that uses acetyl CoA to generate electron carrier molecules needed in the electron-transport chain is important for powering the cell. Which of the names below is not one of those commonly used to describe this reaction cycle? A) tricarboxylic acid cycle B) Krebs cycle C) oxaloacetic acid cycle D) citric acid cycle 8 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: 48. Two molecules of CO2 are produced after the completion of a single citric acid reaction cycle. Where does the required oxygen come from? A) water B) phosphates C) molecular oxygen D) acetyl CoA 49. In steps 6 and 7 of glycolysis, A) the final outcome is the conversion of an aldehyde to a carboxylic acid with the production of ATP and NADH. B) the final outcome is the conversion of a carboxylic acid to an aldehyde with the production of ATP and NADH. C) production of ATP occurs as the enzyme of step 7, a kinase, phosphorylates ADP. D) A and C E) B and C 50. Step 3 in glycolysis requires the activity of phosphofructokinase to convert fructose 6-phosphate into fructose 1,6-bisphosphate. Which of the following molecules is an allosteric inhibitor of this enzyme? A) Pi B) AMP C) ADP D) ATP Section 3: Extra Credit (3 points) 51. was awarded the 2003 Nobel Prize in Chemistry for his discovery of aquaporins. Aquaporins are water-channel proteins that move water molecules through the cell membrane. A) Dr. Hans Krebs B) Dr. Stanley Prusiner C) Dr. Peter Agre D) Dr. Linus Pauling E) Dr. James Waston 9 (Version 1) Introduction to Cell Biology Name: September 30, 2010 Student ID: Answers 1. B. 2. A. 3. B. 4. A. 5. A. 6. B. 7. B. 8. B. 9. A. 10. A. 11. B. 12. B. 13. A. 14. A. 15. B. 16. D. 17. C. 18. D. 19. D. 20. D. 21. B. 22. C. 23. D. 24. A. 25. B. 26. A. 27. B. 28. A. 29. D. 30. B. 31. B. 32. C. 33. C. 34. B. 35. D. 36. A. 37. B. 38. D. 39. D. 40. D. 41. B. 42. C. 43. C. 44. D. 45. C. 46. D. 47. C. 48. A. 49. D. 50. D. 51. C.  10 (Version 1)