328
EXAMINATION BIO 1 FOR EACH QUESTION, SELECT THE MOST INCORRECT ANSWER
Mark your answers on the op-scan sheet with a No.2 pencil. If you change your answer, be sure to erase thoroughly. There are 20 questions on this examination so be sure to answer all of them. Fill in your name and SBU ID number (NOT YOUR SS#) on the answer sheet. 1. Membrane Potential a. The primary current carriers in biological systems are ions in solution. b. Ions in solution are surrounded by a tight shell of water molecules known as a hydration shell. c. Negatively charged ions are called anions. d. Ohm's Law can be used to describe the movement of ions through ion channels. e. Intracellular fluids have a relatively high concentration of sodium ions. 2. Membrane Potential a. Assuming that Cl- ions make a negligible contribution to setting the membrane potential, if, [K+]i = 125 mM, [K+]o = 5 mM, [Na+]i = 12 mM and [Na+]o = 120 mM and the membrane is 50 times more permeable to K+ ions than to Na+ ions the membrane potential will be approximately 71 mV. b. The Goldman equation gives the relationship between the membrane potential and the ion concentrations and ion permeabilities for permeant ions. c. The equilibrium potential for a potassium ion, which has an internal concentration of 200 mM and an external one of 2 mM, is exactly -116 mV. d. An ion is at electrochemical equilibrium when its electrical potential is equal and opposite to its chemical potential. e. According to Ohm's law, if the membrane potential is 70 mV the K+ current will be an inward current, assuming normal external and internal K+ ion concentrations. 3. Membrane Potential a. The electrical potential inside a mammalian cell is negative with respect to the outside of the cell. b. Separation of charged ions across the capacitance of the cell membrane produces the resting membrane potential. c. The principle of electroneutrality states that there are an equal number of positive and negative charges in the bulk solutions inside and outside of the cell. d. The membrane potential of a cell is the difference between the intracellular electrical potential and the extracellular one. e. Membrane pumps produce a separation of charge across the cell membrane by pumping cations out of the cell and anions into the cell. 4. Cell Physiology a. Transporters are needed for polar or charged molecules to cross cell membranes. b. The energy necessary for facilitated transport is provided by the chemical concentration gradients of the transported molecules. c. Membrane pumps use the chemical energy derived from the hydrolysis of ATP. d. Facilitated diffusion is so called because the transporter simply facilitates the diffusion of a solute across the membrane down its concentration gradient.
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BIO 328 e.
EXAMINATION 1
The intracellular calcium concentration is 2 mM.
5. Ion Channels a. Potassium channels are tetramers. b. In the potassium channel, permeation is dependent on interactions between the ions and the carbonyl oxygen atoms of the protein backbone. c. One subunit of a simple (not voltage-gated) potassium channel has two membrane spanning domains. d. Permeation of potassium ions through K+ channels is achieved by having a low energy barrier to the movement of the ion from the bulk aqueous solution into the selectivity filter of the channel. e. The selectivity filter of K+ channels is a very flexible structure that undergoes large movements as ions pass through the channel. 6. Ion Channels a. The inner hydration shell of K+ ions appears to be made up of 2 rings of 4 water molecules. b. The selectivity filter of the potassium channel mimics the hydration shell of potassium ions in solution by providing a ring of carbonyl oxygen atoms. c. Sodium channels exclude potassium ions and pass sodium ions. d. Sodium ions have a smaller ionic radius than potassium ions. e. Electrostatic attraction between K+ ions in the pore contributes to the movement of K+ ions through the selectivity filter of the potassium channel. 7. Action Potentials a. A threshold voltage level must be reached in order to trigger an action potential. b. Action potentials are triggered by depolarization. c. For a typical voltage-gated ion channel, when the membrane potential is rapidly shifted from 80 mV to +10 mV the channel first opens and then inactivates. d. The action potential is an active response due to the presence of voltage-gated ion channels in the cell membrane. e. The absolute refractory period is a period when most of the K+ channels are inactivated. 8. Action Potentials a. Subthreshold currents produce linear voltage responses in a typical neuron's cell membrane. b. Saltatory conduction is a fast electrical conduction that takes place in myelinated nerve fibers. c. At rest, the permeability of the membrane to Na+ ions is 50 times less than to K+ ions. d. At the resting membrane potential the activation gates of both the voltage-gated sodium and potassium channels are closed. e. The length constant of an axon is inversely proportional to the axonal membrane resistance. 9. Action Potentials a. Local current flow is essential for the propagation of an action potential down an axon.
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BIO 328 b. c. d. e.
EXAMINATION 1
Neurons are functionally polarized, so that electrical information normally flows from the cell body through the axon to the nerve terminal. Potassium channels activate more slowly than sodium channels during an action potential. Propagation of an action potential along a nerve fiber is mediated by local circuit currents. The peak of an action potential depends on the size of the stimulus that elicited the action potential.
10. Synaptic Transmission a. A cation selective ligand-gated ion channel can be converted to an anion selective channel by modifying two amino acids in the intermediate charge ring within the ion channel. b. A single epsp at the neuromuscular junction is much larger than that required to reach the action potential threshold. c. At an inhibitory synapse, the electrical response in the postsynaptic cell is called an inhibitory postsynaptic potential (ipsp). d. At the neuromuscular the junction, neurotransmitter acetylcholine is released following a presynaptic action potential. e. At the reversal potential of the acetylcholine receptor (approximately 0 mV) the inward flux of Na+ ions is much greater than the outward flux of K+ ions. 11. Synaptic Transmission a. A synapse requires structural components provided by both the pre- and postsynaptic cells. b. Acetylcholine released into the synaptic cleft at the neuromuscular junction is broken down by the enzyme acetylcholinesterase, which hydrolyzes acetylcholine into acetate + choline. c. Activation of an inhibitory synapse results in a hyperpolarization of the postsynaptic cell. d. GABA receptors mediate a hyperpolarizing response in the post-synaptic membrane. e. Binding of acetylcholine to the acetylcholine binding site on the nicotinic acetylcholine receptor triggers the hydrolysis of ATP, which provides the energy necessary to induce the conformational change that opens the channel. 12. Synaptic Transmission a. After synaptic vesicles fuse with the plasma membrane of the synaptic terminal, the vesicle membrane is retrieved by endocytosis and recycled into new synaptic vesicles. b. Agonist-gated receptors act much faster than G-protein-linked receptors. c. An excitatory post-synaptic potential moves the membrane potential towards the threshold for activation of sodium channels. d. Hydropathy plots can be used to identify hydrophobic membrane spanning regions in a protein. e. Binding of glutamate to its receptor induces a conformational change that leads to the opening of the channel and the passage of Cl- ions. 13. Synaptic Transmission
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BIO 328 a. b. c.
EXAMINATION 1
d. e.
Bernard Katz was the first person to deduce the role of Ca 2+ ions in synaptic transmission. Miniature epsps are much smaller than the epsp at the neuromuscular junction. Neuromodulation is mediated by slow synapses driven by a large variety of neurotransmitters and peptides, including glutamate, dopamine and Substance P. Neurotransmitter molecules are released from the synaptic terminal into the synaptic cleft by exocytosis. The acetylcholine receptor is a tetramer.
14. Synaptic Transmission a. Typical EPSPs in the central nervous system are relatively small and require spatial and temporal summation in order to reach threshold. b. Ca2+ influx through voltage-gated Ca2+ channels increases the intracellular Ca 2+ concentration, which triggers neurotransmitter release. c. During synaptic transmission the change in ionic permeability of the postsynaptic membrane occurs following binding of the neurotransmitter to specific postsynaptic receptors. d. There are two classes of neurotransmitter receptors: Ligand-Gated Ion Channels and G-Protein Linked Receptors. e. NMDA and AMPA receptors cannot coexist in the same synapse. 15. Synaptic Transmission a. EPSPs in the central nervous system typically are relatively small and require spatial and temporal summation in order to reach threshold. b. Exocytosis of synaptic vesicles is a complex event that involves a large number of different proteins. c. Following synchronous activation of a large number of individual acetylcholine receptors by neurotransmitter release the channels close with an exponential time course. d. NMDA receptors are permeable to Ca 2+ ions. e. Voltage-gated Ca2+ channels in the nerve terminal are located at a significant distance away from vesicle release sites. 16. Heart a. The SA node receives innervation from both the parasympathetic and sympathetic nervous systems. b. Activation of G protein subunits is ended when the subunit of the G protein hydrolyzes GTP. c. At rest, the heart rate is mainly controlled by the parasympathetic nervous system. d. Electrical activity in the normal heart is initiated by pacemaker cells located in the sinoatrial node. e. Acetylcholine, released by parasympathetic nerves, increases the slope of the pacemaker potential. 17. Heart a. Gap junction channels are made up of two halves each provided by opposing cells in the gap junction. Each hemichannel has 6 subunits. b. Muscarinic receptors in SA node cells couple to the G protein Gi and the beta/gamma subunits of Gi activate IK,ACh channels.
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BIO 328 c. d. e.
EXAMINATION 1
Myocytes in the ventricles are connected together with gap junctions to make an electrical syncytium. Purkinje fibers are part of the ventricular conducting system Activation of G protein subunits is ended when the subunit of the G protein hydrolyzes ATP.
18. Heart a. There is a large pacemaker potential in sinoatrial nodal myocytes. b. The cardiac action potential is much longer than the nerve or skeletal muscle one. c. The cardiac myocardium is an electrical syncytium with individual myocytes interconnected by gap junctions. d. The cardiac rhythm rate is under the control of two branches of the autonomic nervous system e. The atria and ventricles are electrically connected at multiple points to enhance the passage of electrical excitation from the atria to the ventricle. 19. Human Genetics a. A primary purpose of the Human Genome Project was to generate a series of overlapping maps including cytogenetic, sequence, disease genes and physical maps. b. Single gene disorders generally follow simple Mendelian inheritance rules with the complication that incomplete penetrance can confuse the genetic analysis. c. One form of epilepsy is due to mutations in the KCNQ2 and KCNQ3 potassium channel genes. d. Individual differences are caused in part by differences in the DNA sequence of genes. e. Long QT syndrome (LQTS) is caused by mutations in voltage gated Ca2+ channels. 20. Human Genetics a. Mutations in human ion channel genes can produce a range of genetic diseases including epilepsy and cystic fibrosis. b. The first symptom in LQTS may be sudden death. c. The benign clinical manifestation of LQTS is a long QT interval. d. The QT interval is a measure of the ventricular action potential duration. e. Single nucleotide polymorphisms are specific locations in the DNA sequence where everyone in the general human population shares the same sequence.
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