BISC 307 Spring 2009 Exam 1 Answers 3 pts 1 Breathing raises the concentration of O2 in the blood lowers the concentration of CO2 in the blood and raises blood pH According to the principles of negative feedback regulation which one of the following is most likely to stimulate an increase in breathing d a an increase in blood O2 concentration b a decrease in blood CO2 concentration c an increase in blood pH d none of the above would stimulate an increase in breathing 4 pts 2 In a typical mammalian cell which one of the following is most likely to occur if the Na K ATPase is inhibited with ouabain c a a decrease in intracellular Na b an increase in intracellular K c an increase in intracellular Ca2 d an increase in Na glucose co transport e an increase in Na Ca2 exchange 3 pts 3 Which one of the following statements is false d a A slice of potato immersed in a hypotonic aqueous solution is likely to swell b Sodium dependent glucose transport is an example of secondary active transport c The glucose transporter can move glucose in either direction across the plasma membrane d The symptoms of cystic fibrosis are consequences of a defect in the epithelial Na channel e Epithelial cells involved in the transport of water from one body compartment to another are likely to express aquaporin molecules 4 pts 4 Imagine two aqueous solutions A and B that are separated by a membrane that is permeable to K but not to Cl or H2O Solution A is 100 mM KCl and solution B is 1 mM KCl Which one of the following statements is most likely to be true e a Solution B is hyperosmotic compared to solution A b K ions will diffuse from solution A to solution B until the K of both solutions is 50 5 mM c K ions will diffuse from solution B to solution A until the K of both solutions is 50 5 mM d Over time osmosis will increase the volume of solution A and decrease the volume of solution B e Solution A is electrically negative with respect to solution B 6 pts 5 The effects of hormones on target cells can be tremendously amplified by intracellular signaling pathways In the case of the cAMP signaling pathway which steps are responsible for this amplification ANS Amplification occurs at several steps Binding of one hormone to its receptor can activate several stimulatory G proteins Each of these can activate several adenylyl cyclase enzymes each of which generates many molecules of cAMP These cAMP molecules in turn activate many protein kinase A molecules each of which can phosphorylate many target proteins Some of the target proteins may be enzymes whose stimulated or inhibited activity further amplifies Exam 1 Posted Answers doc Page 1 of 6 5 pts 6 When the neurotransmitter GABA binds to its postsynaptic receptors the Cl permeability of the postsynaptic membrane increases In the adult mouse brain this causes hyperpolarizing IPSPs In young postnatal mice however GABA causes depolarizing EPSPs Neuronal resting potentials are constant at about 70 mV and plasma Cl does not change over the lifespan Which one of the following statements best explains how GABA shifts from having an excitatory action to an inhibitory action d a In young mice GABA stimulates an active transporter that pumps Cl in b In young mice the GABA activated channel is permeable to Na as well as Cl c In young mice the GABA activated channel is permeable to K as well as Cl d Intracellular Cl is high in young mice and lower in adult mice e None of the above explains the developmental shift in GABA s action 4 pts 7 Indicate the immediate effect of each of the manipulations below on the resting membrane potential of a typical neuron by writing D for depolarization H for hyperpolarization or NC for no change in the blanks Write only one answer in each blank ANS a NC b D c H d D a Exposure to tetrodotoxin b An increase in extracellular K concentration c Opening of Cl channels if ECl is more negative than the membrane potential d Opening an equal number of Na and K channels 1 2 3 4 5 5 pts 8 The diagram on the right shows a segment of a squid axon through which an action potential is propagating in the propagation direction shown The graph below direction shows the value of the membrane ENa potential at various positions along the axon The horizontal axes of the graph V 0 m and the drawing correspond Areas 1 5 ECl are particular locations along the axon EK Answer each question below by writing Distance along axon one number in the blank ANS a 4 b 5 c 3 d 1 e 2 a Area where for most voltage gated Na channels both the activation and inactivation gates are open b Area where most voltage gated Na channels are closed and outward flow of current is depolarizing the membrane c Area where for most voltage gated Na channels the activation gate is open but the inactivation gate is closed d Area where all channels are in their resting configuration e Area where only voltage gated K channels delayed rectifier channels are open 4 pts 9 Imagine that you isolate a single axon and arrange it on stimulating electrodes as shown in the diagram below The cell body or soma end is to the left and the presynaptic terminal end is to the right You then stimulate both ends simultaneously to elicit an action potential at each end Which one of the following best describes what would happen to the action potentials when they propagate to the middle of the axon and meet a Exam 1 Posted Answers doc Page 2 of 6 Stimulate SOMA END Stimulate TERMINAL END a The action potentials will cancel when they collide they will not propagate past the midpoint b The action potentials will sum temporally creating an action potential roughly twice as large c Each action potential will pass through the other and propagate to the opposite end of the axon d The action potentials will never meet because they can only propagate in the normal direction soma terminal 3 pts 10 Which of the following is not a general characteristic of postsynaptic potentials PSPs a a PSPs are all or none in amplitude b PSPs decrease in amplitude with distance away from the synapse c PSPs are produced by neurotransmitter molecules binding to chemically gated channels d PSPs produced near the axon hillock have a stronger effect than those produced in the dendrites 10 pts 11 Succinylcholine also known as sux is a drug used in emergency medicine to rapidly but temporarily paralyze muscles for example when it is necessary to insert a tube into the trachea of a patient that cannot breathe Sux binds to and activates the nicotinic