BISC 307 Spring 2011 Exam 1 Answers 3 pts 1 In the diagram on the right a semipermeable membrane separates chambers A and B both of which are filled with water The membrane is permeable to water but impermeable to NaCl A B 1 atm When 1 atm of hydrostatic pressure is applied to A water flows from A to B at 10 ml min Chamber A is drained then re filled with an aqueous solution of NaCl with an osmotic pressure of 1 atm A B NaCl B Which of the following statements about the third situation is true a At electrochemical equilibrium chamber A will be 58 mV more negative than chamber B b Na ions will diffuse from chamber A to chamber B down their concentration gradient c If one re applies a hydrostatic pressure of 1 atm to chamber A water will flow from A to B at 20 ml min d If no hydrostatic pressure is applied to chamber A water will flow from B to A at 10 ml min e There will be no net movement of water f None of the above Answer in box d 6 pts 2 Write a number in each blank to match each term on the left with its most appropriate definition on the right A given definition should only be used only once or not at all 1 causes cells to be positive inside compared to outside a Na K ATPase 2 b Ca ion 2 movement of water down its concentration gradient c facilitated diffusion 3 secondary active transporter 4 Brownian motion d Na glucose symporter e CFTR 5 a peripheral membrane protein f osmosis 6 trigger for exocytosis in many cells 7 passive transport across cell membranes 8 electrogenic ion pump 9 epithelial Cl channel ANSWER a 8 b 6 c 7 d 3 e 9 f 2 10 epithelial Na channel 2 pts 3 If you wanted to add glucose to a 20 mM solution of KCl in order to make it isoosmotic with a 150 mM solution of NaCl what would be the final concentration of glucose needed Answer in box a 300 mM d 130 mM b 280 mM e 100 mM c 1 c 260 mM f 80 mM 3 pts 4 Imagine a membrane that is permeable to Na but not to Cl This membrane separates two aqueous solutions in which the only solute is NaCl The concentration of NaCl on side 1 is much higher than on side 2 Which one of the following will occur a Na will move until the concentration on side 1 is the same as the concentration on side 2 b Cl will move until the concentration on side 1 is the same as the Answer in box concentration on side 2 c Cl will move from side 1 to side 2 down its concentration gradient f d A potential will develop across the membrane positive on side 1 e There will be no movements of ions f None of the above will occur 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 the signal 2 7 pts 6 In general what roles do Ca ions play in the intracellular signaling mediated by inositol trisphosphate IP3 ANS IP3 causes the intracellular release of Ca2 stored in the smooth endoplasmic reticulum These Ca2 ions can trigger exocytosis bind to calmodulin and activate the calmodulindependent protein kinase and have other effects IP3 can also be converted to IP4 within the cell which can enhance the function of Ca2 channels 3 pts 7 The distribution of ions across the membrane of a particular nerve cell is such that ECa 100 mV ENa 60 mV ECl 70 mV EK 90 mV resting potential 80 mV and threshold for generating action potentials is 60 mV This nerve cell receives a variety of different types of synaptic inputs In the box write an E or I next to each choice to note whether the synapses described would be excitatory E or inhibitory I a a synapse which increased pNa in the postsynaptic membrane E b a synapse which increased pK in the postsynaptic membrane I c a synapse which increased pCl in the postsynaptic membrane I 3 pts 8 The trace below shows a recording of current on the vertical axis flowing through a single voltage gated K channel as a function of time on the horizontal axis The membrane potential is held at 70 mV EK is 90 mV and ENa is 50 mV Imagine that you suddenly changed the membrane potential to 30 mV Write Increase Decrease or No Change in each of the blanks below to indicate the changes you would expect to see in these single K channel currents 5 pA 0 2 a Mean time interval between channel openings Decrease b Mean channel open time how long channel stays open before closing No Change c Mean amplitude of single channel current Increase 7 pts 9 Explain the ionic basis of the refractory period that follows an action potential in a typical unmyelinated axon ANS The refractory period is caused by two ionic events The first event is inactivation of voltagegated Na channels Depolarization has two effects on Na channels opening of the activation gate followed with a delay by closing of the inactivation gate An inactivated channel cannot re open to contribute inward current to another action potential until the gates have re set to their resting configurations The second event is the delayed opening of voltage gated K channels The resulting increase in K permeability generates an outward current that moves the membrane potential in the negative direction towards the K equilibrium potential EK This persistent rise in K permeability makes it less likely that any depolarizing influence will bring the membrane to threshold for generation of another action potential thus it extends the duration of the refractory period 3 pts 10 Which of the following statements about acetylcholinesterase at the neuromuscular junction is correct Read this question carefully a Acetylcholinesterase is the neurotransmitter at the neuromuscular junction Answer in box b Acetylcholinesterase is stored in vesicles in the presynaptic terminal c Acetylcholinesterase prolongs the action of the neurotransmitter making f the endplate potential larger than it would otherwise be d Acetylcholinesterase paralyzes skeletal muscle by binding to acetylcholine receptors e Acetylcholinesterase binds to receptor sites on the presynaptic membrane f None of the above statements is true 3 pts 11 Which of the