Biophysics MCQS &&

1. What is the necessary condition for generation of spike potentials in smooth muscle cells ?

a ) sufficient intra - cellular calcium deposits ;

b ) reaching membrane depolarization threshold ;

c ) sufficient density of voltage - gated Na * channels .

b ) reaching membrane depolarization threshold ;

2. Spike potentials in smooth muscles are defined as :

a ) action potentials ;

b ) slow waves ;

c ) Ca equilibrium potentials .

a ) action potentials ;

3. Smooth muscle tissue is build of this type of cells :

a ) cylindrical cells ;

b ) spindle - shaped cells ;

c ) relatively small hexagonally - shaped cells .

b ) spindle - shaped cells ;

4. " Slow waves " are present in :

a ) gastrointestinal smooth muscle tissue ;

b ) bronchial smooth muscle tissue ;

c ) arterial smooth muscle tissue .

a ) gastrointestinal smooth muscle tissue ;

5. Slow waves are changes in the membrane potential in certain smooth muscles :

a ) due to input from the nervous system ;

b ) not due to stimuli from the nervous system or endogenous substances ;

c ) due to endogenous substances .

b ) not due to stimuli from the nervous system or endogenous substances ;

6. Is there a functional relationship between slow waves and spike potentials in smooth muscle cells ?

a ) yes , slow waves can trigger spike potentials ;

b ) there is no known functional dependence ;

c ) yes , spike potentials can trigger slow waves .

a ) yes , slow waves can trigger spike potentials ;

7. The dynamics of ion flow during spike potentials is :

a ) Na influx → depolarization , K efflux → repolarization ;

b ) Ca² * influx → depolarization , K efflux → repolarization ;

c ) Ca² + efflux → depolarization , Nat influx → repolarization

b ) Ca² * influx → depolarization , K efflux → repolarization ;

8. In the cytosol Ca² * ions bond to , and activate a protein which plays a critical role in the contraction of the smooth muscle . This protein is :

a ) calmodulin ;

b ) tropomyosin ;

c ) troponin C.

a ) calmodulin ;

9. Which of the following muscles do not have an ordered sarcomere structures ?

a ) skeletal muscles ;

b ) cardiac muscle ;

c ) smooth muscles

c ) smooth muscles

10. Which ion channels permit the Ca² + ion influx , necessary for the spontaneous phasic contractions of smooth muscles ?

a ) receptor - regulated channels ( triggered by ligands ) ;

b ) voltage - gated ( membrane potential dependent ) ;

c ) stretch - regulated ( mechanical forces on the membrane ) .

b ) voltage - gated ( membrane potential dependent ) ;

11. What type of contraction results in smooth and striated muscles when the intervals between consecutive action potentials are shorter than the duration of muscle fiber contractions ?

a ) single contraction ;

b ) phasic contractions ;

c ) complete or incomplete tetanus .

c ) complete or incomplete tetanus .

12. Which is the best description of the membrane potential of striated muscles when there are no muscle contractions ?

a ) rhythmic low frequency fluctuations below threshold excitation- formation for slow waves ;

b ) steady resting potential ;

c ) slow depolarization initiated from pacemaker cells .

b ) steady resting potential ;

13. What is the source of Ca2 + needed for the contraction of striated skeletal muscles ?

a ) from intracellular Ca² + depots ;

b ) influx of Ca2 + from the extracellular fluid into the sarcoplasm , which leads to additional Ca² * release form intracellular depots ;

c ) through suppression of the activity of the calcium pumps ( which remove intracellular Ca² " ) .

a ) from intracellular Ca² + depots ;

14. What type of membrane channels are activated during action potential propagation along the sarcolemma of striated muscle cells ?

a ) voltage - gated sodium channels ;

b ) calcium channels , regulated by ryanodine receptors ;

c ) voltage - dependent calmodulin receptors .

a ) voltage - gated sodium channels ;

15. The sarcoplasmic reticulum of smooth muscle cells can be characterized as :

a ) very elaborate ;

b ) moderately developed ;

c ) not elaborate .

c ) not elaborate .

16. Are there motor endplates in smooth muscle tissues ?

a ) yes ;

b ) no ;

c ) sometimes .

b ) no ;

17. Phasic contraction in smooth muscle cells are responsible for :

a ) peristaltic movement ;

b ) the heartbeat ;

c ) release of neurotransmitter molecules .

a ) peristaltic movement ;

18. The existence of " slow waves " in the membrane potential is characteristic for :

a ) phasic smooth muscle cells ;

b ) tonic smooth muscle cells ;

c ) neurons .

a ) phasic smooth muscle cells ;

19. Blood vessels are predominately build of :

a ) tonic smooth muscle tissue ;

b ) phasic smooth muscle tissue ;

c ) satiated muscle tissue .

a ) tonic smooth muscle tissue ;

20. Activation of the enzyme myosin light chain kinase ( MLCK ) leads to :

a ) contraction in smooth muscle cells ;

b ) relaxation in smooth muscle cells ;

c ) initiation of slow waves

a ) contraction in smooth muscle cells ;

21. The basic contraction unit in smooth muscle tissues is :

a ) the smooth muscle cell ;

b ) the smooth muscle fiber ( myofibril ) ;

c ) the fiber bundle , wrapped in connective tissue ( fascicle ) .

b ) the smooth muscle fiber ( myofibril ) ;

22. Choose the correct statement :

a ) in visceral smooth muscle tissue , found in hollow organs , fiber single unit ) , and individual cells communicate via nexuses ( gap junctions ) ;

b ) in visceral smooth muscles , found in hollow organs , each muscle cell is innervated individually ( as a multi - unit ) , and individual cells communicate via gap junctions ;

c ) in visceral smooth muscles , found in hollow organs , each muscle cell is innervated individually , and individual cells do not communicate .

a ) in visceral smooth muscle tissue , found in hollow organs , fiber single unit ) , and individual cells communicate via nexuses ( gap junctions ) ;

23. Choose the set of characteristics that describes best smooth muscle contractions :

a ) voluntary , slow , large energy expenditure ;

b ) involuntary , fast , low energy expenditure ;

c ) involuntary , slow , low energy expenditure .

c ) involuntary , slow , low energy expenditure .

24. The thin myofilaments in smooth muscle cells are build of :

a ) 4 types of contractile proteins ;

b ) 2 types of contractile proteins ;

c ) 3 types of contractile proteins .

c ) 3 types of contractile proteins ;

25. The basis of the thin myofilaments in smooth muscle tissue is the protein :

a ) myosin ;

b ) actin ;

c ) troponin .

b ) actin ;

26. The basis of the thick myofilaments in smooth muscles is the protein :

a ) myosin ;

b ) actin ;

c ) tropomyosin .

a ) myosin ;

27. Choose the correct statement regarding discrete ( multi - unit ) smooth muscles :

a ) in discrete smooth muscle tissue , found in hollow organs , each cell is innervated separately , and individual cells communicate via nexuses ( gap junctions ) ;

b ) in discrete smooth muscles each cell is innervated individually , thus cells do not communicate directly ;

c ) in discrete smooth muscles , found in hollow organs , fibers are innervated together in bundles , and individual cells communicate via nexuses ( gap junctions ) .

b ) in discrete smooth muscles each cell is innervated individually , thus cells do not communicate directly ;

28. In smooth muscles fibers the ratio between actin and myosin ( thin / tick ) fibers is :

a ) random ;

b ) 5 : 1 to 13 : 1 ;

c ) always 6 : 1 .

b ) 5 : 1 to 13 : 1 ;

29. Thin myofilaments in smooth muscle tissues are build of the following proteins :

a ) myosin , actin , titin , and troponin ;

b ) actin and tropomyosin ;

c ) actin , titin , and calmodulin .

b ) actin and tropomyosin ;

30. What is the spacial orientation of the smooth muscle contractile apparatus ?

a ) random orientation ;

b ) aligned in one direction , along the length of the fiber ;

c ) aligned in two perpendicular directions .

a ) random orientation ;

31. What is the source of Ca² + needed for the contraction of the smooth muscles ?

a ) from the extracellular medium , where calcium concentration is much greater than in the intracellular space ;

b ) from in the intracellular depots , found in the sarcoplasmic reticulum ;

c ) both a . and b

c ) both a . and b

32. What is the role of Ca² * in the smooth muscle contraction ?

a ) bonds to regulatory protein calmodulin ;

b ) bonds to the myosin molecule ;

c ) Ca² + does not affect smooth muscle contraction .

a ) bonds to regulatory protein calmodulin ;

33. Which intracellular factors lead to a smooth muscle relaxation ?

a ) factors that activate the enzyme myosin light chain phosphatase ;

b ) factors that inhibit the enzyme myosin light chain phosphatase ;

c ) factors that activate the enzyme myosin light chain kinase .

a ) factors that activate the enzyme myosin light chain phosphatase ;

34. Which intracellular factors lead to a smooth muscle contraction ?

a ) factors that activate the enzyme myosin light chain phosphatase ;

b ) factors that inhibit the enzyme myosin light chain phosphatase ;

c ) factors that activate the enzyme myosin light chain kinase .

c ) factors that activate the enzyme myosin light chain kinase .

35. What is the role of the enzyme myosin light chain kinase ( MLCK ) in the smooth muscle contraction ?

a ) it shortens the thin myofilaments and , after phosphorylation , it bends actin into a spiral ;

b ) it phosphorylates the 20 - kDa myosin light chain ( MLC 20 ) of the myosin molecule , allowing for cross - bridge formation between thin and thick myofilaments ;

c ) it interacts with ATP and the thin myofilaments , delivering energy for the contraction .

b ) it phosphorylates the 20 - kDa myosin light chain ( MLC 20 ) of the myosin molecule , allowing for cross - bridge formation between thin and thick myofilaments ;

36. What is the role of the enzyme myosin light chain phosphatase ( MLCP ) in the smooth muscle relaxation ?

a ) after contraction , it lengthens the thick myofilaments ;

b ) it de - phosphorylates the 20 - kDa myosin light chain ( MLC 20 ) of the myosin molecule , disrupting the bonding of myosin with the dense bodies of the membrane ;

c ) it de - phosphorylates the 20 - kDa myosin light chain ( MLC 20 ) of the myosin molecule , disrupting the cross - bridge formation between thin and thick fibres .

c ) it de - phosphorylates the 20 - kDa myosin light chain ( MLC 20 ) of the myosin molecule , disrupting the cross - bridge formation between thin and thick fibres

37. What is the function of protein calmodulin for the smooth muscle contraction ?

a ) it forms a complex with four calcium ions , which activates the enzyme myosin light chain kinase ( MLCK ) ;

b ) does not affect smooth muscle contraction ;

c ) it transports Ca ++ from the cellular membrane to the protein troponin C.

a ) it forms a complex with four calcium ions , which activates the enzyme myosin light chain kinase ( MLCK ) ;

38. The electro - mechanical coupling of smooth muscles is :

a ) muscle contraction stimulated with electric current ;

b ) the relation between action potential and subsequent increase of intracellular Ca ++ leading to contraction ;

c ) the directed movement of Ca² + ( electric current ) in the cytosol towards the contractile apparatus ( mechanical ) .

b ) the relation between action potential and subsequent increase of intracellular Ca ++ leading to contraction ;

39. What is a spike potential ?

a ) a rapid change in the membrane potential due to a slow wave ;

b ) action potential in certain smooth muscle cells ;

c ) electric phenomenon due to re - orientation of the myofilaments in the smooth muscle cell .

b ) action potential in certain smooth muscle cells ;

40. Is there a relationship ( and if there is then what type ) between spike potentials and the Ca² + concentration in the cytosol ?

a ) yes there is . Spike potentials are caused in part by Ca² + influx and that leads to increase in the intracellular calcium ;

b ) no ;

c ) yes , there is . Spike potentials cause Ca² * efflux which leads to decrease of the calcium concentration . in the cytosol .

a ) yes there is . Spike potentials are caused in part by Ca² + influx and that leads to increase in the intracellular calcium ;

41. Is there a relationship ( and what type ) between spike potentials and the strength of contraction of smooth muscles ?

a ) no ;

b ) yes , it is proportional . The greater the number of spike potentials the stronger the contraction ;

c ) Yes . An increased number of spike potentials will decrease the strength of muscle contraction .

b ) yes , it is proportional . The greater the number of spike potentials the stronger the contraction ;

42. Is there a difference in the properties of phasic and tonic smooth muscle contractions ?

a ) no , they are two names for the same basic process ;

b ) yes . Phasic contractions occur with certain repetition of few times per minute , and tonic contractions rise slowly and can last many minutes ;

c ) yes . Tonic contractions occur with regular frequency and amplitude , and phasic contractions are slow and can last many minutes .

b ) yes . Phasic contractions occur with certain repetition of few times per minute , and tonic contractions rise slowly and can last many minutes ;

43. Spike potentials occur in the following type of cells :

a ) hepatocytes ;

b ) cardiac contractions ;

c ) phasic smooth muscle contractions .

c ) phasic smooth muscle contractions .

44. Tonic smooth muscle contractions are characterized by :

a ) generation of autonomous action potential ;

b ) the lack autonomous action potential ;

c ) positive membrane potential .

b ) the lack autonomous action potential ;

45. Phasic smooth muscles are characterized by :

a ) their steady membrane potential ;

b ) their function to maintain the tonus in blood vessels ;

c ) sinusoidal variation in the membrane potential .

c ) sinusoidal variation in the membrane potential .

46. During smooth muscle contraction , the concentration Ca² + in the cytosol increases to :

a ) 10^-5 mol /l

b ) 10^-7 mol /l

c ) 10^7 mol /l

a ) 10^-5 mol /l

47. Spike potentials in smooth muscles provide :

a ) Ca2+ influx from the extracellular space into the cytosol ;

b ) Ca2+ efflux from the cytosol into the extracellular space ;

c ) bidirectional transfer of Ca²+ across the membrane , leading to equilibrium .

a ) Ca2+ influx from the extracellular space into the cytosol ;

48. In smooth muscle cells , the complex 4Ca - Calmodulin activates :

a ) the light chain of myosin phosphatase ;

b ) myosin light chain kinase ( MLCK ) ;

c ) the Ca2+ regulated K+ channels .

b ) myosin light chain kinase ( MLCK ) ;

49. Cat pumps work to :

a ) increase Ca² + concentrations in the cytosol ;

b ) decrease Ca² + concentrations in the cytosol ;

c ) do not affect cytosol concentrations of Ca² + .

b ) decrease Ca² + concentrations in the cytosol ;

50. The two known Ca² + depots in the sarcoplasmic reticulum ( IP3 - regulated and Ryanodine regulated ) are :

a ) independent of each other ;

b ) one depot with two different channels ;

c ) dependent on the membrane potential .

a ) independent of each other ;

51. What are the elastic properties of muscles ?

a ) the ability to stretch ;

b ) the ability to return to initial size after a stretch ;

c ) the ability to contract .

b ) the ability to return to initial size after a stretch ;

52. In the living body all muscles maintain certain level of tension called tonus . During contraction this tonus will :

a ) increase ;

b ) decrease ;

c ) stay the same .

a ) increase ;

53. Why are smooth muscles ( SM ) called autonomous ?

a ) because SM react to external stimuli ;

b ) because excitations can be generated within the SM tissue ;

c ) because SM can remain de - excited for long periods .

b ) because excitations can be generated within the SM tissue ;

54. Smooth muscle contraction is triggered by increased intra - cellular concentration of this type of ions :

a ) K+

b ) Ca² +

c ) Na+

b ) Ca² +

55. In the human body , smooth muscles are found in :

a ) most of the internal organs

b ) the skeletal muscles

c ) non - nodal tissue of the heart muscle .

a ) most of the internal organs

56. The structural muscle tissue found in arterial walls is of this type :

a ) phasic smooth muscle

b ) tonic smooth muscle

c ) striated muscle cells working in tandem with tonic smooth muscle cells .

b ) tonic smooth muscle

57. Is there a relationship between slow wave membrane potentials and the contractions in smooth muscle cells ?

a ) yes , slow waves are related with tonic contractions

b ) yes , slow waves are related with phasic contractions

c ) there is no relation between slow waves and contractions .

b ) yes , slow waves are related with phasic contractions

58. What is characteristic about the membrane potential of the stomach ?

a ) rhythmic fluctuations with low frequency and below threshold

b ) constant potential at rest

c ) depolarization reaching threshold once every second .

a ) rhythmic fluctuations with low frequency and below threshold

59. In smooth muscle cells , all intra - cellular factors that activate myosin light chain kinase ( MLCK ) will cause :

a ) relaxation

b ) contraction

c ) neither

b ) contraction

60. Ion channels are :

a ) temporary openings ( pores ) in the cellular

b ) membrane proteins that span across the lipid membrane ; bilayer and come in contact with the extra- and intra cellular environments ;

c ) mobile membrane proteins that move across the lipid bilayer from the extracellular into the intracellular space .

b ) membrane proteins that span across the lipid membrane ; bilayer and come in contact with the extra- and intra cellular environments ;

61. What is the role of the electrostatic filter in ion channels ?

a ) it changes the ion channel state : open or closed ;

b ) it selects the ion species that can pass through the channel

c ) it interacts with the electrically charged heads of the phospholipid molecules in order to change conformation

b ) it selects the ion species that can pass through the channel

62. Is it possible for CI ions to pass through a Ca² * ion channel ?

a ) no , because Cl ' ions are too large to fit the narrow channel ;

b ) yes , they can ;

c ) no , because the Ca2 + ion channel has an electrostatic selectivity filter with negative charge .

c ) no , because the Ca2 + ion channel has an electrostatic selectivity filter with negative charge .

63. How many gates do voltage - gated Na * channels have ?

a ) one ;

b ) two ;

c ) three .

b ) two ;

64. Which of the following membrane conditions activate the voltage - gated ( potential - dependent ) ion channels ?

a ) depolarization of the plasma membrane ;

b ) hyper - polarization of the plasma membrane ;

c ) keeping the membrane potential unchanged for period of 50 ms

a ) depolarization of the plasma membrane ;

65. Which of the following combinations of factors determine the activation time of the voltage - gated ion channels ?

a ) the membrane potential and the pH of the cytosol ;

b ) the level of hyper - polarization of the membrane and the specific channel gate kinetics ;

c ) the level of membrane depolarization and the specific ion channel kinetics .

c ) the level of membrane depolarization and the specific ion channel kinetics .

66. What activates ligand - gated ( receptor - regulated ) ion channels ?

a ) changes in the membrane potential ;

b ) interaction between the corresponding ligand and the receptor , regulating the ion channel ;

c ) the process of internalization of the receptor .

b ) interaction between the corresponding ligand and the receptor , regulating the ion channel ;

67. What prevents inorganic ions from moving through the phospholipid membrane ?

a ) the equal concentrations of ion species on both sides of the membrane ( isotonicity ) ;

b ) inorganic ions are water - soluble . The phospholipid bilayer does not permit the passage of water soluble substances ;

c ) the ion passage is prevented by the higher hydrostatic pressure inside the cell .

b ) inorganic ions are water - soluble . The phospholipid bilayer does not permit the passage of water soluble substances ;

68. Are ion channels completely impermeable for all but the ion species that give the channel's name ?

a ) no , other similar ions can pass with low probability ;

b ) yes , they permit only the ion species that give the channel's name ;

c ) no , large organic molecule can also pass through the channels .

a ) no , other similar ions can pass with low probability ;

69. Is ion channel traffic regulated and how ?

a ) no , ion traffic is not regulated ;

b ) ion traffic is regulated through conditional gating mechanisms ;

c ) ion traffic is regulated by pressure gradients .

b ) ion traffic is regulated through conditional gating mechanisms ;

70. Which of the following descriptions refers to ion channels ?

a ) a random , temporary formation of pores in the lipid bilayer ;

b ) protein structures that transport ions across the membrane with the expense of energy ;

c ) protein structures that allow passive transport of inorganic ions .

c ) protein structures that allow passive transport of inorganic ions .

71. Choose the best fitting description for ion channels from the following :

a ) membrane protein structures that span across the membrane , and under certain conditions provide selective ion transport between extra and intra cellular spaces ;

b ) membrane lipid structures that span across the membrane , and under certain conditions allow a water - filled passage between extra and intra cellular spaces ;

c ) membrane protein structures that provide uninterrupted ion transport between intra and extra cellular spaces .

a ) membrane protein structures that span across the membrane , and under certain conditions provide selective ion transport between extra and intra cellular spaces ;

72. What forces drive ions through the ion channels ?

a ) electrochemical gradients ;

b ) hydrostatic pressure ;

c ) osmotic pressure .

a ) electrochemical gradients ;

73. What type of transport takes place through ion channels when they are activated :

a ) passive ;

b ) active ;

c ) passive when moving in , and active when moving out of the cell

a ) passive ;

74. Which ion types can pass through the calcium - activated potassium channels ?

a ) calcium ions ;

b ) potassium ions ;

c ) sodium ions .

b ) potassium ions ;

75. Depolarization of the plasma membrane activates this type of ion channels :

a ) receptor - regulated ( ligand - gated ) channels ;

b ) voltage - gated channels ;

c ) none of the above .

b ) voltage - gated channels ;

76. Nifedipine and Verapamil are channel blockers for this type of ions :

a ) calcium membrane channels ;

b ) sodium channels located on cellular organelles ;

c ) potassium membrane channels .

a ) calcium membrane channels ;

77. The repolarization phase of spike potentials is due to the opening of this type of channels :

a ) calcium - activated potassium channels ;

b ) voltage - gated calcium channels ;

c ) sodium channels .

a ) calcium - activated potassium channels ;

78. TTX is a blocker of this type of channels :

a ) voltage - gated membrane sodium channels found in neurons ;

b ) potassium membrane channels found in smooth muscle tissue with spontaneous bioelectric activity ;

c ) non - activating sodium channels found in the cardiac sinoatrial node .

a ) voltage - gated membrane sodium channels found in neurons ;

79. The passive trans - membrane transport of neutral molecules , when possible , is driven by :

a ) their electrochemical gradient ;

b ) their electrical gradient ;

c ) their concentration gradient .

c ) their concentration gradient .

80. Choose the correct statement regarding ligand - gated ion channels :

a ) they are inactivated by complementarity ;

b ) they are activated by changes in the membrane potential ;

c ) the ligand - receptor interaction leads to conformational changes in the protein structure .

c ) the ligand - receptor interaction leads to conformational changes in the protein structure .

81. Conduction of inorganic ions through the plasma membrane is carried by :

a ) endocytosis ;

b ) narrow water - filled channels with diameter of 0.3-0.65mm ;

c ) phagocytosis .

b ) narrow water - filled channels with diameter of 0.3-0.65mm ;

82. Ion transport through the ion channels is :

a ) unidirectional ;

b ) active ;

c ) passive .

c ) passive

83. During the resting state of the cell , the Na * electrochemical gradient points :

a ) from the extracellular into the intracellular space ;

b ) from the intracellular into the extracellular space ;

c ) in both directions .

a ) from the extracellular into the intracellular space ;

84. The bonding of a specific channel blocker with a target ion channel will result in :

a ) inhibition of the passive transport of the particular ion species ;

b ) inhibition of the active transport of the particular ion species ;

c ) inhibition of the passive ion transport in the entire body .

a ) inhibition of the passive transport of the particular ion species ;

85. The phospholipid bilayer of the plasma membrane allows passive diffusion of :

a ) small hydrophobic molecules : oxygen , nitrogen , and carbon dioxide ;

b ) small inorganic ions : sodium , potassium , and magnesium ;

c ) large organic molecules : amino acids , peptides , and glucose

a ) small hydrophobic molecules : oxygen , nitrogen , and carbon dioxide ;

86. Which of the following names of ion channel structures is not part of the accepted terminology ?

a ) narrow tunnel ;

b ) opening :

c ) gating mechanism .

b ) opening :

87. The default state of ion channels is :

a ) open ;

b ) closed ( deactivated ) ;

c ) inactivated .

b ) closed ( deactivated ) ;

88. The type of transport through the ion channels is called :

a ) active ;

b ) passive , driven by existing gradients ;

c ) passive for some ions , and active for others .

b ) passive , driven by existing gradients ;

89. What is the electric charge of the narrow tunnels in ion channels ?

a ) positive ;

b ) negative ;

c ) opposite to the electric charge of the ion species that pass through the channel .

c ) opposite to the electric charge of the ion species that pass through the channel .

90. In which of the following cases will a voltage - gated ( potential - dependent ) ion channel be activated ?

a ) when the membrane potential is higher than the activation threshold for the ion channel

b ) when the membrane potential is at resting level

c ) when the membrane potential is lower than the activation threshold for the ion channel

a ) when the membrane potential is higher than the activation threshold for the ion channel

91. Trans - membrane ion transport through ion channels is driven by :

a ) osmotic gradients ;

b ) equilibrium potentials ;

c ) electrochemical gradients .

c ) electrochemical gradients .

92. Ion channels are ( choose the best ) :

a ) integral proteins ;

b ) transmembrane proteins ;

c ) peripheral proteins .

b ) transmembrane proteins ;

93. An ion channel that could be activated by a hormone neurotransmitter , mediator , or other biologically active substance is called :

a ) potential - dependent channels ;

b ) ligand - gated channels ;

c ) Ca2+ dependent channels .

b ) ligand - gated channels ;

94. Which of the following types of ion channels permit calcium , needed for the phasic contractions in smooth muscles , into the cell ?

a ) ligand - gated channels ;

b ) voltage - gated channels ;

c ) stretch - gated channels ( mechano - sensitive ) .

b ) voltage - gated channels ;

95. The sarcomere is :

a ) a protein involved in the contraction of striated muscle fibres ;

b ) an element of the striated muscle fiber , located between two Z - discs ;

c ) a structure that produces second messengers in muscle cells .

b ) an element of the striated muscle fiber , located between two Z - discs ;

96. Thin myofilaments in striated muscle cells are composed of :

a ) 4 type of proteins ;

b ) 1 type of protein ;

c ) 3 types of proteins .

c ) 3 types of proteins

97. The major protein component of the thin myofilaments in striated muscle cells is :

a ) myosin

b ) actin ;

c ) troponin .

b ) actin ;

98. The major protein component of the thick myofilaments in striated muscle cells is :

a ) myosin ;

b ) actin ;

c ) troponin .

a ) myosin

99. In skeletal muscles the ratio between actin and myosin filaments is :

a ) undetermined ;

b ) it varies from 6 : 1 to 15 : 1 ;

c ) always 6 : 1 .

c ) always 6 : 1 .

100. The myosin molecule in striated muscles has :

a ) two active sites : for bonding with Tropomyosin C , and ATP ;

b ) three active sites : for bonding with F - actin , Ca , and ATP ;

c ) two active sites : for bonding with F - actin , and ATP .

c ) two active sites : for bonding with F - actin , and ATP .