Bio

4. Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes A. are a phospholipid bilayer. B. are a phospholipid bilayer between two layers of hydrophilic proteins. C. are a single layer of phospholipids and proteins.D. consist of protein molecules embedded in a fluid bilayer of phospholipids. E. consist of a mosaic of polysaccharides and proteins

D

34. The movement of the hydrophobic gas nitrous oxide (N2O) (laughing gas) into a cell is an example of A. diffusion across the lipid bilayer. B. facilitated diffusion. C. active transport. D. osmosis. E. cotransport

A

40. Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A. CO2 B. an amino acid C. glucose D. K+ E. starch

A

25. The cell membranes of Antarctic ice fish might have which of the following adaptations? A. very long chain fatty acids B. branched isoprenoid lipids C. a high percentage of polyunsaturated fatty acids D. a higher percentage of trans fatty acids E. no cholesterol

C

10. The plasma membrane of winter wheat are able to remain fluid when it is extremely cold by A. increasing the number of cholesterol molecules present B. closing protein channels C. decreasing the number of hydrophobic protein channels D. replacing saturated fatty acids with unsaturated fatty acids E. using fatty acids with longer tails

D

13. The hydrophilic regions of a membrane protein are most likely A. present only unmusical cells B. associated with the fatty acid regions of the lipids C. in the interior of the membrane D. exposed on the surface of the membrane E. either on the surface or inserted into the interior of the membrane

D

19. When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are A. peripheral proteins. B. phospholipids. C. carbohydrates. D. integral proteins. E. cholesterol molecules

D

27. Why are lipids and proteins free to move laterally in membranes? A. The interior of the membrane is filled with liquid water. B. Lipids and proteins repulse each other in the membrane. C. Hydrophilic portions of the lipids are in the interior of the membrane. D. There are only weak hydrophobic interactions in the interior of the membrane. E. Molecules such as cellulose can pull them in various directions

D

28. Over the years, the fluid mosaic model has been refined based on recent experimental findings. In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model? A. The membrane is only fluid across a very narrow temperature range. B. Proteins rarely move in the membrane. C. Unsaturated lipids are excluded from the membranes and do not contribute to membrane fluidity. D. The concentration of protein molecules appears to be much higher. E. Membrane proteins are made of only acidic amino acids

D

30. Which of the following is true for the evolution of cell membranes? A. The fluid mosaic nature of cell membranes provides the explanation for the evolution of cell membranes. B. Membrane proteins are the sole component responsible for the evolution of cell membranes. C. The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids. D. All components of membranes evolve as a result of natural selection. E. An individual organism selects its preferred type of cell membrane for particular functions

D

14. When a mouse cell and a human cell are fused, the membrane proteins of the two cells become uniformly distributed over the surface of the hybrid cell. This occurs because A. many proteins can move around within the bilayer B. all proteins are anchored within the membrane C. proteins are asymmetrically distributed within the membrane D. all proteins in the plasma membrane are peripheral E. different membranes contain different proteins

A

16. The presence of cholesterol in the plasma membranes of some animals A. enables the membrane to stay fluid more easily when cell temperature drops. B. enables the animal to remove hydrogen atoms from saturated phospholipids. C. enables the animal to add hydrogen atoms to unsaturated phospholipids. D. makes the membrane less flexible, allowing it to sustain greater pressure from within the cell. E. makes the animal more susceptible to circulatory disorders

A

17. According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids? A. They can move laterally along the plane of the membrane. B. They frequently flip-flop from one side of the membrane to the other. C. They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane. D. They are free to depart from the membrane and dissolve in the surrounding solution. E. They have hydrophilic tails in the interior of the membrane

A

20. Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures? A. The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly. B. Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in their membranes. C. Unsaturated fatty acids are more polar than saturated fatty acids. D. The double bonds block interaction among the hydrophilic head groups of the lipids E. The double bonds result in shorter fatty acid tails and thinner membranes

A

23. A protein that spans the phospholipid bilayer one or more times is A. a transmembrane protein. B. an integral protein. C. a peripheral protein. D. an integrin. E. a glycoprotein

A

31. Which of the following is an example of passive transport? A. facilitated diffusion B. sodium - potassium pump C. phagocytosis D. exocytosis E. pinocytosis

A

32. Osmosis is a specific form of A. diffusion B. pinocytosis C. active transport D. secondary active transport ( co transport ) E. movement of water using carrier proteins

A

46. Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater? A. Water will leave the cells, causing them to shrivel and collapse. B. NaCl will be exported from the red blood cells by facilitated diffusion. C. The blood cells will take up water, swell, and eventually burst. D. NaCl will passively diffuse into the red blood cells. E. The blood cells will expend ATP for active transport of NaCl into the cytoplasm

A

47. 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 glucose solution is increased. But when the glucose concentration of the solution is increased above 10M, the ratio no longer increases. Which of the following is the likely mechanism for glucose transport into these cells? A. facilitated diffusion via carrier protein B. facilitated diffusion via channel protein C. pinocytosis D. active transport E. hydrolysis

A

61. Familial hypercholesterolemia is characterized by which of the following? A. defective LDL receptors on the cell membranes B. poor attachment of the cholesterol to the extracellular matrix of cells C. a poorly formed lipid bilayer that cannot incorporate cholesterol into cell membranes D. inhibition of the cholesterol active transport system in red blood cells E. a general lack of glycolipids in the blood cell membranes

A

63. Which of the following processes does NOT involve the uptake of material into the cell? A. exocytosis B. pinocytosis C. endocytosis D. receptor- mediated endocytosis E. phagocytosis

A

69. The signals that bind to receptors on nearby cells are known as A. paracrine signals B. parastic signals C. autocrine signals D. hormones E. responders

A

70. In what ways do ligand - receptor interactions differ from enzyme - substrate interactions? A. the ligand signal is not usually metabolized into useful products B. receptor - ligand interactions do not obey the laws of mass action C. inhibitors never bind to the ligand binding site D. reversibility never occurs in ligand - receptor interactions E. none of the above; there is no difference between the two

A

74. Which of the following factors would tend to increase membrane fluidity? A. a greater proportion of unsaturated phospholipids B. a greater proportion of saturated phospholipids C. a lower temperature D. a relatively high protein content in the membrane E. a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses

A

8. Contact with ice numbs a persons fingers because at lower temperatures A. membrane fluidity is reduced in the nerve cells B. no ATP can be produced in the fingers C. protein kinases are activated in the nerves D. membranes in the nerve cells unzip E. there are changes in the lipid composition of the membranes in the nerve cells

A

89. In general, a signal transmitted via phosphorylation of a series of proteins A) brings a conformational change to each protein. B) requires binding of a hormone to a cytosol receptor. C) cannot occur in yeasts because they lack protein phosphatases. D) requires phosphorylase activity. E) allows target cells to change their shape and therefore their activity

A

89. Which of the following most likely would be an immediate result of a growth factor binding to its receptor? A) protein kinase activity B) adenylyl cyclase activity C) GTPase activity D) protein phosphatase activity E) phosphorylase activity

A

96. In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling? A) Growth factor ligands do not bind as efficiently to receptors. B) Their lower hormone concentrations elicit a lesser response C) cAMP levels change very frequently. D) Enzymatic activity declines. E) ATP production decreases

A

11. A protein that forms an ion channel through a membrane is most likely A. a peripheral protein B. a transmembrane protein C. a phospholipid D. an enzyme E. entirely outside the phospholipid bilayer

B

2. Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At high temperatures, these regions A. are more fluid than the surrounding membrane. B. are less fluid than the surrounding membrane. C. are able to flip from inside to outside. D. detach from the plasma membrane and clog arteries. E. have higher rates of lateral diffusion of lipids and proteins into and out of these regions

B

26. The formulation of a model for a structure or for a process serves which of the following purposes? A. It asks a scientific question. B. It functions as a testable hypothesis. C. It records observations. D. It serves as a data point among results. E. It can only be arrived at after years of experimentation

B

35. 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 own its concentration gradient D. the concentration of each ink will be higher at one end of the pan than at the other E. no predictions can be made without knowing the molecular weights of the pigment molecules

B

36. 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. hypertonic solution; isotonic solution E. low concentration of water; high concentration of water

B

37. What kinds of molecules pass through a cell membrane most easily? A. large and hydrophobic B. small and hydrophobic C. large polar D. ionic E. monosaccharides such as glucose

B

38. Which of the following is a characteristic feature of a carrier protein in a plasma membrane? A. It is a peripheral membrane protein. B. It exhibits a specificity for a particular type of molecule. C. It requires the expenditure of cellular energy to function. D. It works against diffusion. E. It has few, if any, hydrophobic amino acids

B

5. Which of the following statements about cholesterol molecules is true? A. they help hold a membrane together. B. they alter the fluidity of the membrane. C. they attach to carbohydrates. D. they disrupt membrane function. E. they transport ions across the membrane

B

59. Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean? A. Proton pumps must have evolved before any living organisms were present on Earth. B. Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life. C. The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism. D. Cells of each domain evolved proton pumps independently when oceans became more acidic. E. Proton pumps are necessary to all cell membranes

B

60. A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in A. peroxisomes B. lysosomes. C. Golgi vesicles. D. vacuoles. E. secretory vesicles

B

62. 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 cells

B

64. 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

B

7. House plants adapted to indoor temperatures may die if they are left outdoors, because in a cold environment their A. DNA cannot function B. membranes lack adequate fluidity C. photosynthesis is impaired D. membranes contain too many unsaturated fatty acids E. membranes need more cholesterol

B

75. In what way do the membranes of a eukaryotic cell vary? A. Phospholipids are found only in certain membranes. B. Certain proteins are unique to each kind of membrane. C. Only certain membranes of the cell are selectively permeable. D. Only certain membranes are constructed from amphipathic molecules. E. Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm

B

76. Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A. only target cells retain the appropriate DNA segments. B. intracellular receptors are present only in target cells. C. most cells lack the Y chromosome required. D. only target cells possess the cytosolic enzymes that transduce the testosterone. E. only in target cells is testosterone able to initiate a phosphorylation cascade

B

82. Which of the following is true of steroid receptors? A) The receptor molecules are themselves lipids or glycolipids. B) The receptor may be inside the nuclear membrane. C) The unbound steroid receptors are quickly recycled by lysosomes. D) The concentration of steroid receptors must be relatively high in most cells. E) The receptor molecules are free to move in and out of most organelles

B

85. In which of the following ways do plant hormones differ from hormones in animals? A) Plant hormones interact primarily with intracellular receptors. B) Plant hormones may travel in air or through vascular systems. C) Animal hormones are found in much greater concentration. D) Plant hormones are synthesized from two or more distinct molecules. E) Animal hormones are primarily for mating and embryonic development

B

87. Testosterone functions inside a cell by A) acting as a signal receptor that activates tyrosine kinases. B) binding with a receptor protein that enters the nucleus and activates specific genes. C) acting as a steroid signal receptor that activates ion channel proteins. D) becoming a second messenger that inhibits nitric oxide. E) coordinating a phosphorylation cascade that increases spermatogenesis

B

9. 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 phospholipids B. capacity of lipids to associate and maintain a bilayer organization C. constant length of the fatty acid chain and degree of saturation D. ability of the phospholipid molecule to flip over and trade places with other phospholipid molecules E. asymmetrical distribution of membrane proteins

B

93. In which of the following ways could signal transduction most probably be explored in research to treat cancer? A) removal of serine/threonine phosphate acceptors from transduction pathways in colon pre- cancerous growths B) alteration of protein kinases in cell cycle regulation in order to slow cancer growth C) increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens D) expansion of the role of transduction inhibitors in the cells before they give rise to cancer E) increase in the concentration of phosphodiesterases in order to produce more AMP

B

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 mem brane proteins

C

12. 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

C

18. In order for a protein to be an integral membrane protein it would have to be A. hydrophilic. B. hydrophobic. C. amphipathic, with at least one hydrophobic region. D. completely covered with phospholipids. E. exposed on only one surface of the membrane

C

21. Which of the following is true of integral membrane proteins? A. They lack tertiary structure. B. They are loosely bound to the surface of the bilayer. C. They are usually transmembrane proteins. D. They are not mobile within the bilayer. E. They serve only a structural role in membranes

C

24. Which of these are not embedded in the hydrophobic portion of the lipid bilayer? A. transmembrane proteins B. integral proteins C. peripheral proteins D. integrins E. glycoproteins

C

29. Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature? A. Because the cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium, the membrane must be asymmetrical B. Because cell membranes communicate signals from one organism to another, the cell membranes must be asymmetrical. C. The two sides of a cell membrane face different environments and carry out different functions. D. The chemical constitution of the inner and outer layer of the cell membrane is predetermined by genes. E. Proteins only function on the cytoplasmic side of the cell membrane, which results in the membrane's asymmetrical nature

C

33. The rate at which a substance diffuses is not affected by the A. diameter of the molecules or ions B. temperature of the solution C. color of the substance D. concentration gradient in the system E. both A and B

C

41. Which of the following statements is correct about diffusion? A. It is very rapid over long distances. B. It requires an expenditure of energy by the cell. C. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration. D. It is an active process in which molecules move from a region of lower concentration to one of higher concentration. E. It requires integral proteins in the cell membrane

C

42. 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 out of the plant cells E. diffusion of water from the plant cells

C

43. When a severely dehydrated person 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 of the patient and the cells would collapse B. nutrients are provided by the saline C. it would cause the patient's blood cells to swell and eventually burst D. normal saline is more economical E. distilled water might be contaminated with bacteria

C

45. Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that A. the fresh water and the salt solution are both hypertonic to the cells of the celery stalks. B. the fresh water and the salt solution are both hypotonic to the cells of the celery stalks. C. the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks. D. the fresh water is hypertonic and the salt solution is hypotonic to the cells of the celery stalks. E. the fresh water is isotonic and the salt solution is hypertonic to the cells of the celery stalks

C

48. In the intestine, Na+ and an amino acid bind to the same transport protein that moves the two substances in the same direction. This is an example of A. passive transport B. simple diffusion C. secondary active transport (co transport) D. facilitated diffusion E. none of the above

C

51. Which of the following membrane activities requires energy from ATP hydrolysis? A. facilitated diffusion of chloride ions across the membrane through a chloride channel B. movement of water into a cell C. movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid D. movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell E. movement of carbon dioxide out of a paramecium

C

54. What is the voltage across a membrane called? A. water potential B. chemical gradient C. membrane potential D. osmotic potential E. electrochemical gradient

C

55. The sodium-potassium pump is called an electrogenic pump because it A. pumps equal quantities of Na+ and K+ across the membrane. B. pumps hydrogen ions out of the cell. C. contributes to the membrane potential. D. ionizes sodium and potassium atoms. E. is used to drive the transport of other molecules against a concentration gradient

C

56. The movement of potassium into an animal cell requires A. low cellular concentrations of sodium B. high cellular concentrations of potassium. C. an energy source such as ATP. D. a cotransport protein. E. a potassium channel protein

C

58. Which of the following would increase the electrochemical gradient across a membrane? A. a chloride channel B. a sucrose-proton cotransporter C. a proton pump D. a potassium channel E. both a proton pump and a potassium channel

C

6. Which of the following types of molecules are the major structural components of the cell membrane? A. phospholipids and cellulose B. nucleic acids and proteins C. phospholipids and proteins D. proteins and cellulose E. glycoproteins and cholesterol

C

65. The next component of a signal transduction pathway, after the signal itself, is a(n) A. paracrine molecule B. responder C. receptor D. hormone E. effector molecule

C

66. The signals that bind to receptors of the same cell that made them are known as A. paracrine signals B. parasitic signals C. autocrine signals D. hormones E. responders

C

68. A molecule that binds to the particular three dimensional structure of another molecule's receptor site is known as a(n) A. responder B. receptor C. ligand D. ion channel E. filament

C

77. Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because A. they are species specific. B. they always lead to the same cellular response. C. they amplify the original signal manifold. D. they counter the harmful effects of phosphatases. E. the number of molecules used is small and fixed

C

78. Adenosine is the normal ______ for its membrane receptor. A. antagonist B. enzyme C. ligand D. fatty acid E. carbohydrate moiety

C

79. The difference between pinocytosis and receptor-mediated endocytosis is that A) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well. B) pinocytosis increases the surface area of the plasma membrane, whereas receptor-mediated endocytosis decreases the plasma membrane surface area. C) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity. D) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not. E) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot

C

80. In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis? A) on the outside of vesicles B) on the inside surface of the cell membrane C) on the inside surface of the vesicle D) on the outer surface of the nucleus E) on the ER

C

84. Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding? A) hormonal signaling B) autocrine signaling C) paracrine signaling D) endocrine signaling E) synaptic signaling

C

91. Which of the following is a correct association? A) kinase activity and the addition of a tyrosine B) phosphodiesterase activity and the removal of phosphate groups C) GTPase activity and hydrolysis of GTP to GDP D) phosphorylase activity and the catabolism of glucose E) adenylyl cyclase activity and the conversion of cAMP to AMP

C

94. A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? A) lower cytoplasmic levels of cAMP B) an increase in receptor tyrosine kinase activity C) a decrease in transcriptional activity of certain genes D) an increase in cytosolic calcium concentration E) a decrease in G-protein activity

C

98. Which of the following is the greatest advantage of having multiple steps in a transduction pathway? A) Many of the steps can be used in multiple pathways. B) Having multiple steps in a pathway requires the least amount of ATP. C) Having multiple steps provides for greater possible amplification of a signal. D) Each individual step can remove excess phosphate groups from the cytoplasm. E) Each step can be activated by several G proteins simultaneously

C

99. GTPase activity is important in the regulation of signal transduction because it A) increases the available concentration of phosphate. B) decreases the amount of G protein in the membrane. C) hydrolyzes GTP to GDP, thus shutting down the pathway. D) converts cGMP to GTP. E) phosphorylates protein kinases.

C

49. Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? A. The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution. B. The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution. C. The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution. D. The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution. E. The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution

D

57. Ions diffuse across membranes through specific ion channels A. down their chemical gradients. B. down their concentration gradients. C. down the electrical gradients. D. down their electrochemical gradients. E. down the osmotic potential gradients

D

67.Signals (chemical messengers) that travel to distant cells in the circulatory system are known as A. paracrine signals B. parasitic signals C. autocrine signals D. hormones E. responders

D

68. Vitamin A is a relatively small, lipid soluble molecule that can behave as a hormone. Most likely its receptor A. is a ion channel receptor B. is a protein kinase receptor C. involve a G protein D. is not connected to the plasma membrane E. does not exist; vitamin A does not have a receptor

D

83. What is most likely to happen to an animal's target cells that lack receptors for local regulators? A) They might compensate by receiving nutrients via a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They might not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells

D

86. When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway? A) receptor B) relay molecule C) transducer D) signal molecule E) endocrine molecule

D

88. Which of the following is true of transcription factors? A) They regulate the synthesis of DNA in response to a signal. B) They transcribe ATP into cAMP. C) They initiate the epinephrine response in animal cells. D) They control gene expression. E) They regulate the synthesis of lipids in the cytoplasm

D

95. At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects? A) Estrogen is produced in very large concentration and therefore diffuses widely. B) Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding. C) Estrogen is kept away from the surface of any cells not able to bind it at the surface. D) Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding. E) The subcomponents of estrogen, when metabolized, can influence cell response

D

15. When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that A. the integral membrane proteins are not strong enough to hold the bilayer together. B. water that is present in the middle of the bilayer freezes and is easily fractured. C. hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing. D. the carbon-carbon bonds of the phospholipid tails are easily broken. E. the hydrophobic interactions that hold the membrane together are weakest at this point

E

22. The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is A. to facilitate diffusion of molecules down their concentration gradients. B. to actively transport molecules against their concentration gradients. C. to maintain the integrity of a fluid mosaic membrane. D. to maintain membrane fluidity at low temperatures. E. to mediate cell-to-cell recognition

E

3. Which of the following is NOT one of the functional roles of a membrane protein? A. transferring signals from outside the cell to inside the cell B. allowing movement of molecules that would otherwise be excluded by the lipid components of the membrane C. facilitating the transport of macromolecules across the membrane D. facilitating the transport of water across the membrane E. stabilizing the lipid bilayer

E

39. Which of the following statements about diffusion is false? A. diffusion does not require ATP B. Diffusion continues until the molecular concentrations are in equilibrium C. in diffusion, molecules move from an area of greater concentration to an area of lesser concentration D. diffusion is a random process E. simple diffusion depends on specific carrier proteins

E

44. Water passes quickly through cell membranes because A. the bilayer is hydrophilic. B. it moves through hydrophobic channels. C. water movement is tied to ATP hydrolysis. D. it is a small, polar, charged molecule. E. it moves through aquaporins in the membrane

E

50. When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur? A. The cell will burst. B. The cell membrane will lyse. C. Plasmolysis will shrink the interior. D. The cell will become flaccid. E. The cell will become turgid

E

52. Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal? A. Sodium and glucose compete for the same binding site in the cotransporter. B. Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient. C. Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. D. The cotransporter can also transport potassium ions. E. A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose

E

53. The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of A. passive diffusion. B. facilitated diffusion. C. active transport. D. osmosis. E. cotransport

E

66. Which of the following statements is true? A. for most ligand-receptor complexes, binding is favored B. ligand-receptor interactions are reversible C. many drugs that alter human behavior prevent the binding of receptors' specific ligands D. both A and B E. all of the above

E

67. Signal ligands can be divided into 2 general classes according to their receptors. Which of the following are the 2 kinds of receptors? A. plasma membrane and ion channels B. plasma membrane and protein kinase C. ion channel and cytoplasmic D. G protein-linked and protein kinase E. plasma membrane and cytoplasmic

E

69. 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

E

71. A benefit of the many steps involved in protein kinase cascade is that they allow for A. activation or inhibition of many enzymes B. amplification of the signal C. distribution of the signal throughout the inside of the cell D. variation in the response E. all of the above

E

72. How does a protein kinase cascade amplify an intercellular signal? A. protein kinase molecules open cell junctions, amplifying the intercellular signal B. the activated G protein binds and activates a second protein, amplifying the signal C. nitric oxide opens cell channels, which allows protein kinase molecules to move quickly from cell to cell D. second messengers create short cuts that create multiple cascades E. once activated, receptor kinase molecule can trigger the activation of thousands of proteins

E

73. Many signal transduction pathways cause A. alterations in gene expression B. upregulation of genes C. the switching off of genes D. an alteration in the abundance of enzymes E. all of the above

E

81. When protein membrane receptors are activated, what usually happens? A) A change occurs in intracellular ion concentration. B) The receptors open and close in response to protein signals. C) A change occurs on only one membrane surface: exterior or interior. D) The receptor preferentially binds with lipid or glycolipid signal molecules. E) The receptor changes conformation after binding with signal polypeptides

E

90. Which of the following statements is true of signal molecules? A) When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules. B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. C) In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus. D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule. E) Protein kinase A activation is one possible result of signal molecules binding to G-protein- coupled receptors

E

92. The function of phosphatases in signal transduction is best described as to A) move the phosphate group of the transduction pathway to the next molecule of a series. B) prevent a protein kinase from being reused when there is another extracellular signal. C) amplify the transduction signal so it affects multiple transducers. D) amplify the second messengers such as cAMP E) inactivate protein kinases and turn off the signal transduction.

E

97. Sutherland discovered that the signaling molecule epinephrine A) brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane. B) causes lower blood glucose by binding to liver cells. C) interacts with insulin inside muscle cells. D) interacts directly with glycogen phosphorylase. E) elevates cytosolic concentrations of cyclic AMP

E