Ion Channels and Neuron Function: Membrane Potentials and Neurotransmission - Prof. Cynthi, Study notes of Humanities

Download Ion Channels and Neuron Function: Membrane Potentials and Neurotransmission - Prof. Cynthi and more Study notes Humanities in PDF only on Docsity! Review for the ISAT 351 First Exam Updated on 1/24/01 This is not a comprehensive list. Rather it is meant an aid in getting you started in thinking about the topics that will be covered on this exam. Topics that have been or will be covered before the first exam: Nerve signal transmission Muscle contraction Signal Transduction Protein Processing and Sorting Vision The cytoskeleton Exam Format: ~30-40 points of short answer and multiple choice ~30-40 points of short essay, short problems, outlines or diagrams ~2 ten point longer essay, problems or diagrams Even though I haven’t explicitly covered everything on the exam, there may be some questions that I hope that you will be able to figure out from the information that I did cover. Guidelines for Exam Answers: Courtesy of The Human Anatomy and Physiology Case Study Project (HAPCS) http://www.niagara.edu/~bcliff/hapcssuc.html If a question asks: "Name..." – Your answer should supply the name of something. Example: Name the process by which the cytoplasm of a eukaryotic cell divides to produce two cells. Answer: cytokinesis If a question asks: "What is..." – The correct answer requires you to identify (or give a measurement of) the item. Example: "What is the role of voltage-gated potassium channels in producing the action potential?" Answer: The opening of the voltage-gated potassium channels causes the repolarization and hyperpolarization of the membrane potential at the end of the action potential. If a question asks: "Explain..." - You should provide an explanation in YOUR OWN WORDS of what is being asked? (Don’t merely reiterate what was in the lecture or in the book.) 1 Example: "Explain the difference between an ion channel and a pump." Answer: An ion channel is a membrane protein that permits ions to passively move across the cell membrane from regions of high concentration to regions of low concentration. A pump is a membrane protein that actively transports substances across the cell membrane from regions of low concentration to high concentration." If a question asks: List..." – Your answer should provide a list of ALL of the items requested. Example: "List at least two regulatory roles for Ca2+ in muscle contraction." Answer: 1. Ca2+ is involved in exocytosis of neurotransmitter containing vesicles in the synaptic knob. 2. Ca2+ binds to troponin-C, and is said to be the trigger for skeletal muscle contraction. If a question asks: "How..." - You should describe a process, a mechanism, or a series of cause and effect events whereby something occurs. Example: "How does ATP use by skeletal muscles lead to contraction?" Answer: ATP binds to the myosin crossbridge formed between the thick and thin filaments and causes the myosin head to be released from its active, binding site on actin. The hydrolysis of ATP then causes the myosin head to be reoriented and reactivated (reenergized) in preparation for its reattachment to another actin molecule, swiveling of the myosin head, and the exertion of the force of contraction. If a question asks: "Propose..." - Your answer should present a logical, coherent series of steps/actions that would SOLVE the problem. Example: "Propose a way to treat cancer that relies upon what you know about the causes of uncontrolled growth of cells." Answer: Since uncontrolled growth in many cancer cells is associated with abnormalities in protooncogenes and tumor suppressor genes, it would be reasonable to intervene in the activities of these genes or the proteins that are made from them. For cancers arising from defects in protooncogenes, it would be useful to pharmacologically inhibit the actions of the growth-promoting oncogenes once they are produced or to enhance the counterbalancing actions of existing tumor-suppressor genes. Conversely, for cancers arising from a loss of tumor- suppressor gene activity, it would be useful to also suppress the actions of protooncogenes or to restore the normal actions of the tumor suppressor genes by gene therapy or by giving pharmacological agents that mimic the actions of the tumor suppressor proteins that have been lost. Review Questions 1. Which of the following statements about transmission across a typical chemical synapse is NOT true? a. Neurotransmitter molecules are stored in vesicles in the synaptic knob. b. Action potentials trigger chemical changes that make the neurotransmitter vesicles fuse with the plasma membrane of the transmitting cell. c. Vesicles containing neurotransmitter diffuse to the receiving cell's plasma membrane. d. The binding of neurotransmitter to receptors opens ion channels in the membrane of the receiving cell. 2. In a resting neuron 2 The time-dependent change in the membrane potential in the figure shown above is called a. the action potential. b. the resting potential. c. the threshold potential. d. hyperpolarization. During the portion of the curve marked “B” a. only the K+ channel is open. b. only the Na+ channel is open. c. both the K+ and Na+ channels are open. d. neither the K+ nor the Na+ channels are open. The threshold value for the initiation of the change in membrane potential in the figure shown above is a. 20 mV b. 40 mV c. 60 mV d. -60 mV During the portion of the cycle marked “C” a. only the K+ channel is open. b. only the Na+ channel is open. c. both the K+ and Na+ channels are open. d. neither the K+ nor the Na+ channels are open. answer: b The state indicated by the portion of the cycle marked “D” is called a. depolarization. b. repolarization. c. hyperpolarization. d. hypopolarization. 13. The specific connection between nerve cells and target cells is called a. an axon. b. a dendrite. c. a synaptic vesicle. d. a synapse. 14. The function of acetylcholinesterase is to 5 time (milliseconds) a. prevent the fusion of synaptic vesicles with the plasma membrane. b. degrade acetylcholine to acetate and choline in the synaptic cleft. c. add acetyl CoA to choline to form acetylcholine. d. stimulate release of acetylcholine from synaptic vesicles. 15. Release of acetylcholine from synaptic vesicles in the nerve cells is triggered by a. Ca2+ uptake. b. ATP hydrolysis c. neurotransmitter uptake. d. K+ uptake. 16. Parkinson’s disease is a neurological disorder that is associated with a. overproduction of gama-aminobutyric acid. b. underproduction of monoamine oxidase. c. overproduction of dopamine. d. underproduction of dopamine. 17. Neurotransmitter receptors are located within a. gap junctions. b. presynaptic membranes. c. postsynaptic membranes. d. the synaptic cleft. 18. Which of the following statements is TRUE? a. Neurotransmitters bind to their receptor proteins on the same side of the membrane as the ion gate. b. Neurotransmitters bind to their receptor proteins on the exterior face of the receptor protein. c. Neurotransmitters bind to their receptor proteins within the ion pore. d. Neurotransmitters bind to their receptor proteins on the interior face of the receptor protein. 19. Dopamine receptor-blocking drugs are used to treat a. Parkinson’s disease. b. Alzheimer’s disease. c. poisoning by acetylcholinesterase inhibitors. d. psychological diseases such as schizophrenia. 20. Binding of acetylcholine to the acetlycholine receptor protein initiates an action potential in the recipient membrane through a. selectively increasing the inward flow of K+ relative to the influx of Na+. b. decreasing the ionic permeability of the postsynaptic membrane. c. inducing acetylcholine release from the postsynaptic cell. 6 d. transiently opening an ion channel. "Adult zebrafish retina" Muscle Contraction 21. What role do ATP molecules play in the process of contraction of a skeletal muscle fiber? a. ATP molecules cause the cross bridges of thin filaments to bind to thick filaments. b. ATP molecules cause the binding sites for thick filaments to be exposed on thin filaments. c. ATP molecules provide energy to enable myosin cross bridges to change conformation so that they are able to bind to the actin molecules on thin filaments. d. ATP molecules provide energy to enable myosin cross bridges to detach from the actin molecules on thin filaments. 22. Muscle tetany results from depletion of ATP during strenuous or prolonged muscle contraction. Describe what happens during tetany. How does it end? 23. Calcium regulates muscle contraction. Where is it stored? What causes its release? To which protein does it bind? What protein is responsible for returning calcium to its intercellular store? 24. Why are dead people called stiffs? Describe what happens during rigor mortis. 25. What is the difference between fast twitch white muscle fibers and slow twitch red muscle fibers? The Cytoskeleton 26. What subunits make up microtubules? What is the energy source for polymerization? 27. List at least 3 cell functions for microtubules. 28. What molecular motors are associated with microtubules? 29. The transport of neurotransmitter vesicles in nerve cells is one example of the use of microtubules in intercellular transport. Briefly describe how this process occurs. 30. Name at least 5 intermediate fibers and briefly describe the function of each. 31. Actin is the most abundant protein in a typical cell. What kinds of actin are there? How is actin polymerized? What is the energy source for this process? Briefly describe at least three cell functions of actin. 7 a. 220 nm b. 380 nm c. 500 nm d. 750 nm answer: c 7. Human cone cells are sensitive to color because a. light of different wavelengths has different energies which are more or less efficient in activating rhodopsin. b. human cone cells have filters that allow only light of certain wavelengths to penetrate their disc membranes. c. light rays entering the eye are refracted differently, depending on the wavelength and, because the cofactor of rhodopsin is oriented specifically within the disc membranes, rhodopsin activation is sensitive to the angle of refraction. d. cone cells have three different rhodopsin molecules, each of which is maximally sensitive to a different wavelength. answer: d 8. The orientation of the retinal with respect to the plane of the disc membrane is a. parallel. b. perpendicular. c. parallel when it is in the form of 11-cis-retinal, but perpendicular when it is all- trans-retinal. d. perpendicular when it is in the form of 11-cis-retinal, but parallel when it is all- trans-retinal. answer: a 9. When the electron density increases near the nitrogen atom of the Shiff base linkage in rhodopsin, a. the wavelength of the absorption maximum decreases. b. the wavelength of the absorption maximum increases. c. the wavelength of the absorption maximum remains the same. d. there are two absorption maxima in the region between 380 nm and 630 nm. answer: a 10. When opsin is mixed with retinal in vitro, a. neither 11-cis-retinal nor all-trans-retinal will bind. b. both 11-cis-retinal and all-trans-retinal will bind. c. only 11-cis-retinal will bind. d. only all-trans-retinal will bind. answer: c 10 11. Bathorhodopsin is the first metastable product of the photochemical reaction of rhodopsin. The cofactor in bathorhodopsin is a. 11-cis-retinal. b. all-trans-retinal. c. 9-cis-retinal. d. 13-cis-retinal. answer: b 12. Which of the following activates transducin? a. bathorhodopsin b. lumirhodopsin c. metarhodopsin I d. metarhodopsin II answer: d 13. Transducin is a. a Ca2+ binding protein. b. a phosphodiesterase. c. a Na+ channel activator. d. a G protein. answer: d 14. The sequence of events following absorption of a photon of light by a rhodopsin molecule in a rod cell is as follows: a. 1) transducin is activated, 2) phosphodiesterase is activated, 3) cGMP is hydrolyzed, 4) Na+ channels close. b. 1) transducin is activated, 2) cGMP is synthesized, 3) phosphodiesterase is inactivated, 4) Na+ channels close. c. 1) transducin is activated, 2) phosphodiesterase is activated, 3) cGMP is hydrolyzed, 4) Na+ channels open. d. 1) transducin is activated, 2) phosphodiesterase is activated, 3) cGMP is synthesized, 4) Na+ channels open. answer: a 15. When rhodopsin is activated by light, the rod cell is a. depolarized by the transient opening of Na+ ion channels. b. hyperpolarized by the transient closure of Na+ ion channels. c. hypopolarized by the transient opening of Na+ ion channels. d. polarized by the transient opening of Na+ ion channels. answer: b 16. Of the following, which is a single subunit integral membrane protein with a molecular mass of about 38,000? a. transducin 11 b. phosphodiesterase c. gyanlylate cyclase d. opsin answer: d 17. As rhodopsin cycles through excitation by light followed by regeneration, a. 11-cis-retinal is isomerized to all-trans-retinal which is then regenerated in- situ through a process that involves 9-cis-retinal and phosphatidylcholine. b. All-trans-retinal is isomerized to 11-cis-retinal, which is then released from the rhodopsin. The 11-cis-retinal is then transferred to the pigment epithelium where it is converted back to all-trans-retinal. c. 11-cis-retinal is isomerized to all-trans-retinal which is then released from rhodopsin. The all-trans-retinal is transferred to the pigment epithelium where it is converted back to 11-cis-retinal in a series of reactions that involve reduction by NADH, esterification, conversion to 11-cis-retinol, and finally oxidation to form 11-cis-retinal. d. All-trans-retinal is isomerized to 11-cis-retinal, which is then converted back to form all-trans-retinal in a reaction that requires light. answer: c 18. Gyanylate cyclase (the enzyme that converts GTP to cGMP) is strongly inhibited by a. arrestin. b. Na+. c. Ca2+. d. the  subunit of transducin. answer: c 19. Phosphodiesterase is activated by a. phosphorylation at multiple serine and threonine sites. b. a complex between the  subunit of transducin and GTP. c. Na+. d. all-trans-retinal. answer: b 20. The electrochemical potential across the rod cell cytoplasmic membrane is generated by a. the Na+, K+-ATPase. b. the plasma membrane Ca2+-ATPase. c. phosphodiesterase. d. movement of protons across the plasma membrane in response to light activation of rhodopsin. answer: a 12