Question 2 Question 2Skeletal muscle contraction is regulated by acetylcholine (ACh) molecules. Acetylcholine is a signalreleased from neurons that act on muscle cells. ACh receptors on muscle cells consist of five subunits thattogether make a channel. Two of these subunits are alpha subtype. When ACh binds alpha subunits of thereceptor, the channel is opened. That allows Na* ions to flow into the muscle cell.Both alpha subunits of the receptor need to be bound by a molecule of ACh for the channel to open. Inga) What is the highest level of protein structure exhibited by the ACh receptor?b) An experiment was conducted to determine the affinity (Kd) of the ACh receptor for its ligand, ACh.Researchers put 1000 cells expressing the ACh receptor into each of several dishes, then treated each dishwith solutions that varied in their concentrations of ACh (but were otherwise the same). They thenmeasured the fraction of receptors that were bound to ACh in each dish. Their data are shown below.queConcentration of ACh in Solution Percentage of Receptors Boundred an agonist of the AC0%ceptor. What does thisnicotine?0 UM1234567142080959899Make a graph of these data. Consider which variable should be on the x-axis and which should be on the y-axis, and label the axes. If you draw your graph by hand, take a picture and insert it into your write-up.c) Using your graph, estimate the Kd of the receptor for ACh under these experimental conditions. Be sureto include units in your estimate.d) Another research group tries to replicate this experiment. They put the same number and type ofreceptor-expressing cells in dishes and expose them to different concentrations of ACh in a solution.However, the pH of their ACh solution is 5.5, while the pH of the ACh solution used by the first researchgroup was 7.4. Do you expect their estimate of the receptor's Kd to be the same as the estimate obtainedby the first group? Explain.Recall that the ACh receptor is found on the membrane of muscle cells. Opening the channel of thereceptor (and allowing Na+ to flow through into the muscle cell) causes changes in the membrane thatresult in additional channel openings, and eventually, in an electrical signal being sent along the musclefibers. This electrical signal, in turn, causes Ca²+ channels that are embedded in the ER membrane toopen, releasing many Ca²+ ions into the cytoplasm. This increase in the Ca²+ concentration in thecytoplasm triggers muscle contraction.e) Make a simple sketch of a portion of muscle cell, depicting just the ER and the cytoplasm. Show theCa²+ channels in the ER membrane and label the relative concentrations of Ca²+ on each side of the ERmembrane before the cell receives a signal from ACh.you expect it to participate in any hydropf) Based on your sketch, which process allows Ca²+ to flow from the ER into the cytoplasm upon AChfacilitated diffusion active transportsignaling? Choose one: simple diffusionndingthe Aa receptg) In this signaling pathway, Ca²+ serves as which type of signaling molecule?3 h) The release of Ca2+ from the ER amplifies the original ACh signal. Briefly explain why.i) In order for the Ca²+ to stop stimulating the contraction, it has to be returned to the ER. After signaling, doyou expect the process of returning Ca²+ from the cytoplasm to where it is stored in the ER to beaccomplished via active or passive transport? Would it involve the same Ca²+ channel in part (e) or adifferent transporter protein? Explain.j) While ACh signal binding to skeletal muscle results increased muscle contraction, ACh signal bindingto the cardiac muscle results in decreased muscle contraction. What do you think could explain thisdifference?Question 3The ACh receptor is sometimes described as "nicotinic" because nicotine, a stimulant of the central nervoussystem, can also bind to and stimulate these receptors.a) Nicotine is considered an agonist of the ACh receptor. What does this tell you about the effect ofexposing skeletal muscle cells to nicotine?5) The structure of nicotine is: that forms a hydrogen bond with nicotine (green dashed lines) is "lockadel hydrogen bonds it makes with the amino acids leucine (Lou) andcally, water interacts with oxygon in the carbonyl cН.in the nitrogen-hydrogen (N-H) bond of Met. (The diagram alectryptophan, as TrpB, which is important in the receptor-ligandhydrogethe recepNMach part dan amino ac contains the carbonyl oxygen and the nitrogen-hydrogen that parécipate inH bonding water acced? (Hint: look up the structures of teucine and methionins.)Nmaye structure of ACh is:CH3you expect that replacing both the Met and the Leu amino acidslanine (Ala) to affect nicotine binding? Explain your reasoning

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Question 2 Question 2Skeletal muscle contraction is regulated by acetylcholine (ACh) molecules. Acetylcholine is a signalreleased from neurons that act on muscle cells. ACh receptors on muscle cells consist of five subunits thattogether make a channel. Two of these subunits are alpha subtype. When ACh binds alpha subunits of thereceptor, the channel is opened. That allows Na* ions to flow into the muscle cell.Both alpha subunits of the receptor need to be bound by a molecule of ACh for the channel to open. Inga) What is the highest level of protein structure exhibited by the ACh receptor?b) An experiment was conducted to determine the affinity (Kd) of the ACh receptor for its ligand, ACh.Researchers put 1000 cells expressing the ACh receptor into each of several dishes, then treated each dishwith solutions that varied in their concentrations of ACh (but were otherwise the same). They thenmeasured the fraction of receptors that were bound to ACh in each dish. Their data are shown below.queConcentration of ACh in Solution Percentage of Receptors Boundred an agonist of the AC0%ceptor. What does thisnicotine?0 UM1234567142080959899Make a graph of these data. Consider which variable should be on the x-axis and which should be on the y-axis, and label the axes. If you draw your graph by hand, take a picture and insert it into your write-up.c) Using your graph, estimate the Kd of the receptor for ACh under these experimental conditions. Be sureto include units in your estimate.d) Another research group tries to replicate this experiment. They put the same number and type ofreceptor-expressing cells in dishes and expose them to different concentrations of ACh in a solution.However, the pH of their ACh solution is 5.5, while the pH of the ACh solution used by the first researchgroup was 7.4. Do you expect their estimate of the receptor's Kd to be the same as the estimate obtainedby the first group? Explain.Recall that the ACh receptor is found on the membrane of muscle cells. Opening the channel of thereceptor (and allowing Na+ to flow through into the muscle cell) causes changes in the membrane thatresult in additional channel openings, and eventually, in an electrical signal being sent along the musclefibers. This electrical signal, in turn, causes Ca²+ channels that are embedded in the ER membrane toopen, releasing many Ca²+ ions into the cytoplasm. This increase in the Ca²+ concentration in thecytoplasm triggers muscle contraction.e) Make a simple sketch of a portion of muscle cell, depicting just the ER and the cytoplasm. Show theCa²+ channels in the ER membrane and label the relative concentrations of Ca²+ on each side of the ERmembrane before the cell receives a signal from ACh.you expect it to participate in any hydropf) Based on your sketch, which process allows Ca²+ to flow from the ER into the cytoplasm upon AChfacilitated diffusion active transportsignaling? Choose one: simple diffusionndingthe Aa receptg) In this signaling pathway, Ca²+ serves as which type of signaling molecule?3 h) The release of Ca2+ from the ER amplifies the original ACh signal. Briefly explain why.i) In order for the Ca²+ to stop stimulating the contraction, it has to be returned to the ER. After signaling, doyou expect the process of returning Ca²+ from the cytoplasm to where it is stored in the ER to beaccomplished via active or passive transport? Would it involve the same Ca²+ channel in part (e) or adifferent transporter protein? Explain.j) While ACh signal binding to skeletal muscle results increased muscle contraction, ACh signal bindingto the cardiac muscle results in decreased muscle contraction. What do you think could explain thisdifference?Question 3The ACh receptor is sometimes described as &#34;nicotinic&#34; because nicotine, a stimulant of the central nervoussystem, can also bind to and stimulate these receptors.a) Nicotine is considered an agonist of the ACh receptor. What does this tell you about the effect ofexposing skeletal muscle cells to nicotine?5) The structure of nicotine is: that forms a hydrogen bond with nicotine (green dashed lines) is &#34;lockadel hydrogen bonds it makes with the amino acids leucine (Lou) andcally, water interacts with oxygon in the carbonyl cН.in the nitrogen-hydrogen (N-H) bond of Met. (The diagram alectryptophan, as TrpB, which is important in the receptor-ligandhydrogethe recepNMach part dan amino ac contains the carbonyl oxygen and the nitrogen-hydrogen that parécipate inH bonding water acced? (Hint: look up the structures of teucine and methionins.)Nmaye structure of ACh is:CH3you expect that replacing both the Met and the Leu amino acidslanine (Ala) to affect nicotine binding? Explain your reasoning

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Neurotransmitters are endogenous chemical molecules that are produced by neurons of the brain to…