140, Biology Spring 2008 Exam 3 (62 questions) Record your answers on the scantron form provided (use a #2 pencil)
1. The compounds in biological membranes that form a barrier to the movement of hydrophilic materials across the membrane are A. integral membrane proteins. B. carbohydrates. C. lipids. D. nucleic acids. E. peripheral membrane proteins. 2. The plasma membrane of animals contains carbohydrates A. on the inner side of the membrane, facing the cytosol. B. on the outer side of the membrane, protruding into the environment. C. on both sides of the membrane. D. on neither side of the membrane. E. within the membrane. 3. In most biological membranes, the phospholipids are arranged in a A. bilayer, with the fatty acids pointing toward each other. B. bilayer, with the fatty acids facing outward. C. single layer, with the fatty acids facing the interior of the cell. D. single layer, with the phosphorus-containing region facing the interior of the cell. E. bilayer, with the phosphorus groups in the interior of the membrane. 4. Peripheral membrane proteins have A. hydrophobic regions within the lipid portion of the bilayer. B. hydrophilic regions that protrude in aqueous environments on either side of the membrane. C. lateral but not vertical movement within the bilayer. D. control over the rate of diffusion. E. polar regions that interact with similar regions of integral membrane proteins. 5. Houseplants adapted to indoor temperatures may die when accidentally left outdoors in the cold because their A. DNA cannot function. B. membranes lack adequate fluidity. C. photosynthesis is impaired due to problems with membranes D. chloroplasts malfunction due to problems with membranes E. membranes need more cholesterol. 6. A protein that forms an ion channel through a membrane is most likely to be A. a peripheral protein. B. a transmembrane protein. C. a phospholipid. D. an enzyme. E. entirely outside the phospholipid bilayer. 7. The hydrophilic regions of a membrane protein are most likely to be found A. only in muscle cell membranes. B. associated with the fatty acid region of the lipids. C. in the interior of the membrane. D. exposed on the surface of the membrane. E. There is no hydrophilic region in membrane proteins.
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8. A characteristic of plasma membranes that helps them fuse during vesicle formation and phagocytosis is the A. ratio of one protein molecule for every 25 phospholipid molecules. B. capacity of lipids to associate and maintain a bilayer organization. C. constant fatty acid chain length and degree of saturation. D. ability of phospholipid molecules to flip over and trade places with other phospholipid molecules. E. asymmetrical distribution of membrane proteins. 9. The LDL receptor is an integral protein that crosses the plasma membrane, with portions of the protein extending both outside and into the interior of the cell. The amino acid side chains (R groups) in the region of the protein that crosses the membrane are most likely A. charged. B. hydrophilic. C. hydrophobic. D. carbohydrates. E. lipids. 10. When vesicles from the Golgi apparatus deliver their contents to the exterior of the cell, they add their membranes to the plasma membrane. In a non growing cell, the plasma membrane does not increase in size, because A. some vesicles from the Golgi apparatus fuse with the lysosomes. B. membrane vesicles carry proteins from the endoplasmic reticulum to the Golgi apparatus. C. membrane is continually being lost from the plasma membrane by endocytosis. D. new phospholipids are synthesized in the endoplasmic reticulum. E. the phospholipids become more tightly packed together in the membrane. 11. The difference between tight junctions, desmosomes, and gap junctions is that A. desmosomes and gap junctions contain keratin, whereas tight junctions have collagen. B. gap junctions and tight junctions have specialized protein channels called connexons; desmosomes do not. C. tight junctions and desmosomes have mechanical roles, whereas gap junctions facilitate communication between cells. D. desmosomes and gap junctions are found in epithelial tissue, whereas tight junctions are found in nerve cells. E. they all have different functions; however, their structure is the same. 12. Specialized channel proteins called connexons occur in A. the cytoskeleton. B. tight junctions. C. desmosomes. D. plasmodesmata. E. gap junctions. 13. Which of the following statements about diffusion is FALSE? A. Diffusion depends on the intrinsic kinetic energy of molecules. B. Diffusion continues until the concentrations are in equilibrium. C. In diffusion, molecules move from areas of greater concentration to areas of lesser concentration. D. Diffusion is a random process. E. Simple diffusion depends upon specific carrier proteins. 14. Which of the following is an example of passive transport? A. Facilitated diffusion B. The sodiumpotassium pump C. Phagocytosis D. Exocytosis E. Pinocytosis
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15. A concentration gradient of glucose across a membrane means that A. the membrane is thicker on one side with glucose than on the other. B. there are more glucose molecules on one side of the membrane than on the other. C. there is less water on one side of the membrane than on the other. D. the glucose molecules are chemically more tightly bonded on one side than on the other. E. there are more glucose molecules within the membrane than outside the membrane. 16. When placed in water, wilted plants lose their limpness because of A. active transport of salts from the water into the plant cells. B. active transport of salts into the water from the plant cells. C. osmosis of water into the plant cells. D. osmosis of water from the plant cells. E. diffusion of water from the plant cells. 17. The difference between osmosis and diffusion is that A. diffusion is passive transport whereas osmosis is active transport. B. only in diffusion do molecules move from areas of high concentrations to areas of low concentration. C. only diffusion refers to the movement of materials across a semipermeable membrane. D. osmosis refers to the movement of water, whereas diffusion is the movement of any molecules. E. the process of osmosis varies according to the kinds of particles present. 18. If a shallow pan is filled with water, a drop of red ink is placed in one end of the pan, and a drop of green ink is placed in the other end, which of the following will be true at equilibrium? A. The red ink will be uniformly distributed in one half of the pan, and the green ink will be uniformly distributed in the other half of the pan. B. The red and green inks will be uniformly distributed throughout the pan. C. Each ink will move down its concentration gradient. D. The concentration of each ink will be higher at one end of the pan than at the other end. E. No predictions can be made without knowing the molecular weights of the pigment molecules. 19. Osmosis is a specific form of A. diffusion. B. facilitated transport. C. ion channel. D. active transport. E. movement of water by carrier proteins. 20. Osmosis moves water from a region of _______ to a region of _______. A. high concentration of dissolved material; low concentration of dissolved material B. low concentration of dissolved material; high concentration of dissolved material C. hypertonic solution; hypotonic solution D. negative osmotic potential; positive osmotic potential E. low concentration of water; high concentration of water 21. Which of the following molecules is the most likely to diffuse across a cell membrane by simple diffusion? A. Glucose B. Na+ C. A steroid D. A common amino acid E. Cl 22. When a severely dehydrated patient is brought to the hospital, an IV of normal saline is started immediately. Distilled water is not used because A. it would cause water to leave the cells and the cells would collapse. B. nutrients are provided by the saline. C. it would cause blood cells to swell and eventually burst. D. normal saline is more economical. E. the distilled water might be contaminated by bacteria.
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23. When placed in a hypertonic solution, animal cells A. shrink. B. swell. C. burst. D. transport water out. 24. If a red blood cell is placed in an isotonic solution, A. the cell will shrivel. B. the cell will swell and burst. C. the cell will shrivel and then return to normal. D. the cell will swell and then return to normal. E. water moves into and out of the cell at an equal rate.
E. concentrate.
25. Which of the following statements about channel proteins is true? A. They have a central pore of polar amino acids and water. B. They are anchored in the hydrophobic bilayer of the plasma membrane. C. They are surrounded by nonpolar amino acids. D. They are usually gated. E. All of the above 26. How does an ion channel exert its specificity for one ion and not another? A. It is a simple matter of charge and ionic size. B. The ion channel hydrates ions as they pass through. C. The ion channel makes use of aquaporins. D. There are signal exchanges between the ion and the ion channel. E. The ion channels are not specific to ions. 27. In a hypothetical study, cells are placed in a solution of glucose in which the concentration of glucose is gradually increased. At first, the rate at which glucose enters the cells is found to increase as the concentration of the glucose solution is increased. But when the glucose concentration of the solution is increased above 10 mM, the rate no longer increases. Which of the following is the likely mechanism for glucose transport into these cells? A. Facilitated diffusion via a carrier protein B. Facilitated diffusion via a channel protein C. Pinocytosis D. Secondary active transport E. Symport 28. Active transport usually moves molecules A. in the same direction as diffusion moves them. B. in the opposite direction in which diffusion moves them. in C. a direction that tends to bring about equilibrium. D. toward higher pH. E. toward higher osmotic potential. 29. Secondary active transport involves all of the following except A. the direct use of ATP. B. coupling to another transport system. C. use of an existing concentration gradient. D. the plasma membrane. E. the ability to concentrate the transported molecule. 30. In the intestine, Na+ and an amino acid bind to the same transport protein that moves the two substances in the same direction. This type of active transport is called A. a symport. B. an antiport. C. an autoport. D. facilitated tranpsort E. A diffusion mechanism
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31. In the parietal cells of the stomach, the uptake of chloride ions is coupled to the transport of bicarbonate ions out of the cell. This type of transport system is called A. a uniport. B. a symport. C. an exchange channel. D. diffusion. E. an antiport. 32. Receptor-mediated endocytosis is the mechanism for transport of A. clathrin. B. all macromolecules. C. ions. D. cholesterol. E. integral membrane proteins. 33. Phagocytosis, pinocytosis, and receptor-mediated endocytosis all involve A. the intake of large particles. B. invagination of the plasma membrane. C. the export of macromolecules. D. the presence of receptor proteins. E. the intake of fluids by the cell. 34. Which of the following is not a function of eukaryotic or prokaryotic plasma membranes? A. Conversion of glucose energy to ATP. B. Arrangement of enzymes. C. Turning off of a specific cell function. D. Conduction of nerve impulses. E. All of the above are functions of plasma membranes. 35. You are monitoring the diffusion of a small lipid soluble molecule across a membrane. Which of the following will result in the fastest rate of diffusion? A. An internal concentration of 5 percent and an external concentration of 60 percent B. An internal concentration of 60 percent and an external concentration of 5 percent C. An internal concentration of 35 percent and an external concentration of 40 percent D. Both A and B 36. In which of the following is solution X hypotonic relative to solution Y? A. Solution X has a greater solute concentration than solution Y. B. Solution X has a lower solute concentration than solution Y. C. Solution X and solution Y have the same solute concentration. D. None of the above 37. Channel proteins allow ions that would not normally pass through the cell membrane to pass through via the channel. What properties of the proteins are responsible for this? A. The channels are often composed of polar amino acid groups. B. The channels are often composed of hydrophobic amino acid groups. C. Both A and B D. None of the above 38. Sodiumpotassium pumps are common in many cells. Which of the following are necessary for the pumps to work? A. ATP B. A channel protein C. No concentration gradient D. All of the above 39. Which of the following represents potential energy? A. Chemical bonds B. Concentration gradient C. Electric charge imbalance D. Both A and B E. All of the above
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40. Bacterial cells are often found in very hypotonic environments. Which of the following characteristics keeps them from continuing to take on water from their environment? A. The presence of a cell wall allows a buildup of turgor pressure that prevents any more water from entering the cell. B. The presence of a cell wall allows a buildup of tonic pressure that prevents any more water from entering the cell. C. The cell expels water as fast as it takes it up. D. None of the above 41. What can never be created or destroyed? A. Entropy B. Energy C. Free energy only D. Thermal energy only E. Potential energy only 42. During photosynthesis, plants use light energy to synthesize glucose from carbon dioxide and water. However, plants do not use up energy during photosynthesis; they merely convert it from light energy to chemical energy. This process is an illustration of A. increasing entropy. B. chemical equilibrium. C. the first law of thermodynamics. D. the second law of thermodynamics. E. a spontaneous reaction. 43. In any system, the total energy includes usable and unusable energy. The unusable energy is a measure of the disorder of the system and is referred to as A. free energy. B. entropy. C. enthalpy. D. thermodynamics. E. equilibrium. 44. The standard free energy change for the hydrolysis of ATP to ADP + Pi is 7.3 kcal/mol. From this information one can conclude that A. the reaction will never reach equilibrium. B. the free energy of ADP and phosphate is higher than the free energy of ATP. C. the reaction requires energy. D. the reaction is endergonic. E. the reaction is exergonic. 45. Chemical equilibrium A. is a dynamic state. B. represents a state of negative energy change. C. represents a state of positive energy change. D. cannot exist in nature. E. is a state in which G = 0. 46. Which of the following statements about enzymes is FALSE? A. An enzyme changes shape when it binds to a substrate. B. Enzymes lower the activation energy. C. Enzymes are highly specific. D. An enzyme may orient substrates, induce strain, or temporarily add chemical groups. E. Most enzymes are much smaller than their substrates. 47. What is a transition state? A. The place where a substrate molecule binds to an enzyme B. A reactant with high potential energy C. The combination of a substrate and an enzyme D. The state at which the bonds of reactants become more unstable E. The active site where reactants are oriented
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48. The hydrolysis of sucrose to glucose and fructose is exergonic. However, if sucrose is dissolved in water and the solution is kept overnight at room temperature, there is no detectable conversion to glucose and fructose. Why? A. The change in free energy of the reaction is positive. B. The activation energy of the reaction is too high. C. The change in free energy of the reaction is negative. D. This is a condensation reaction. E. The free energy of the products is higher than the free energy of the reactants. 49. Trypsin and elastase are both enzymes that catalyze hydrolysis of peptide bonds. But trypsin only cuts next to lysine and elastase only cuts next to alanine. Why? A. Trypsin is a protein, and elastase is not. B. G for the two reactions is different. C. The shape of the active site for the two enzymes is different. D. One of the reactions is endergonic and the other is exergonic. E. Hydrolysis of lysine bonds requires water; hydrolysis of alanine bonds does not. 50. An active site is A. the part of the substrate that binds with an enzyme. B. the part of the enzyme that binds with a substrate. C. the site where energy is added to an enzyme catalyst. D. the site where enzymes are found in cells. E. None of the above 51. In some cases, a substrateenzyme complex is stabilized by A. hydrogen bonds. B. covalent bonds. C. ionic attractions. D. hydrophobic interactions. E. All of the above 52. The ability of an enzyme to change shape when it binds to its substrate is called A. induced fit. B. enzyme flex. C. the lock-and-key paradox. D. substrate-induced active site shaping. E. enzyme retrofit. 53. Competitive inhibitors of enzymes work by A. fitting into the active site. B. fitting into a site other than the active site. C. altering the shape of the enzyme. D. changing the enzyme into an inactive form. E. increasing the activation energy of the enzyme-catalyzed reaction. 54. An allosteric inhibitor A. decreases the concentration of an inactive enzyme. B. changes the shape of an enzyme. C. increases the concentration of a product. D. changes the shape of a substrate. E. increases the concentration of an enzymesubstrate complex. 55. Negative feedback in a sequence of chemical reactions involves a chemical that appears _______ in the sequence and _______ reaction. A. late; inhibits an earlier B. early; inhibits a later C. early; activates a later D. late; activates an earlier E. late; inhibits a later
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56. To respond to a signal, a cell must have a(n) _______ molecule that can detect the signal. A. paracrine B. receptor C. autocrine D. responder E. All of the above 57. In general, all cell signaling causes A. increased expression of genes. B. an influx of ions. C. protein kinase activity. D. G protein activation. E. a change in receptor conformation. 58. In order, from start to finish, the basic steps of a signal transduction pathway are A. signal, responder, receptor, effects. B. receptor, signal, responder, effects. C. signal, receptor, responder, effects. D. signal, receiver, responder, effects. E. None of the above 59. In what way do ligandreceptor interactions differ from enzymesubstrate reactions? A. The ligand signal is not metabolized into useful products. B. Receptorligand interactions do not obey the laws of mass action. C. Inhibitors never bind to the ligand-binding site. D. Reversibility never occurs in the ligandreceptor interaction. E. The enzymesubstrate reaction and the ligandreceptor interaction do not differ. 60. Which of the following statements is true? A. G proteins contain only one important binding site. B. When a G protein binds to an activated receptor protein, ADP is exchanged for ATP. C. G protein receptors are single proteins that have seven distinct regions that pass through the phospholipid bilayer of the cell membrane. D. G proteins can only activate effector proteins; they cannot inhibit them. E. None of the above 61. A benefit of the many steps involved in protein kinase cascades is that they allow for A. specificity of the response. B. amplification of the signal. C. information originally at the plasma membrane to be communicated to the nucleus. D. Both A and C E. All of the above 62. Second messengers A. are typically very specific in their activity. B. do not amplify a signal. C. have enzymatic activity. D. can be derived from lipids. E. All of the above
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