Membrane Transport – A scientist conducted an experiment that looks at three cha
ID: 3483019 • Letter: M
Question
Membrane Transport – A scientist conducted an experiment that looks at three channels found on the surface of the cell body of a neuron. To determine the types of receptors present, he tested the rate of diffusion for three specific compounds (Na+, K+, Ca2+) across a normal cell membrane: Prior to the start of the experiment, the scientist determined the following concentrations of Na+, K+, Ca2+ outside and inside the cell: (look at picture attached)
a. GRAPHICALLY show the difference in the rates of diffusion between Na+ and K+. Assuming that the cell was unstimulated, what types of channels are being examined for Na+ and K+.
b. Now factor in Ca2+. Assuming there is no ATP present, explain one possible mechanism of the transport of Ca2+. Diagram or explain this mechanism.
c. Based on the answer you provided in B and the mitochondria is functioning properly, what other pump needs to be working in order to keep Ca2+ moving across the cell membrane. Diagram or explain the mechanism of this other pump.
Transport - A scientist conducted an experiment that looks at three channels found on the surface of the cell body , K of a neuron. To determine the types of receptors present, he tested the rate of diffusion for three specific compo Ca) across a normal cell membrane: the cell: r to the start of the nt, the scientist determined the following concentrations of Na", K, Ca outside and inside Outside Concentration Inside Concentration Time 0 100 ions 5 ions 60 ions 100 ions 10 ions 100 ions 40 ions 10 ions Na Ca Ca- Ca Cl- After two hours have passed, he re-examined the concentrations and found: Time 2 hr 75 ions 45 ions 100 ions 80 ions 35 ions 50 ions ions Na Na a. 30 ions GRAPHICALLY show the difference in the rates of diffusion between Na and K'. Assuming that the cell was unstimulated, what types of channels are being examined for Na' and K a. Now factor in Ca2". Assuming there is no ATP present, explain one possible mechanism of the transport of Ca2 Diagram or explain this mechanism. b. d on the answer you provided in B and the mitochondria is functioning properly, what other pump needs to be working in order to keep Ca2 moving across the cell mem brane. Diagram or explain the mechanism of this otherp unp.Explanation / Answer
A.The best-understood and perhaps the most important example of an ion pump is the Na+/ K+-ATPase, which is also called the Na+/ K+ pump This pump is an enzyme embedded in the plasma membrane that hydrolyzes ATP so that Na+ and K+ can be transported against their concentration gradients. As stated above, if Na+ were not continually pumped out, the gradient would rapidly be lost, and cells would swell and burst. For this reason, the Na+/ K+ ATPase is in continual operation: more than a third of the ATP consumed by a resting animal cell is used by this pump. The Na+/K+ pump brings two K+ ions in and three Na+ ions out for every molecule of ATP hydrolyzed. An important feature of this mechanism is that ATP hydrolysis and ion transport are tightly coupled—ATP is not hydrolyzed unless the ions are transported.
B.. The nerve impulse reaches the nerve terminal and depolarizes the plasma membrane of the terminal. This opens voltage-gated Ca2+ channels in this membrane. Ca2+ flows into the nerve terminal, which triggers the localized release of acetylcholine into the synaptic cleft
C.The acetylcholine binds to nAchR channels, allowing Na+ to flow into the muscle cell, causing a localized membrane depolarization. The local depolarization of the muscle cell plasma membrane opens voltagegated Na+ channels in this membrane, allowing more Na+ to enter. This opens neighboring voltage-gated Na+ channels, creating a large depolarization (or action potential) that spreads to involve the entire plasma membrane.
The depolarization of the entire plasma membrane results in the opening of Ca2+ channels in the sarcoplasmic reticulum. Ca2+ then rushes into the cytosol, and its sudden increase in concentration triggers a series of events that cause the muscle cell to contract. To end the process of contraction, Ca2+ must be removed from the cytosol of both the nerve terminal and the muscle cell. In both cells, the Na+/Ca2+ exchanger pumps Ca2+ out of the cell using the energy of the Na+ gradient.
The Na+/K+-ATPase pumps Na+ back out of the cell, maintaining the Na+ gradient. In the muscle cells, the Ca2+- ATPase, located in the membrane of the SR, pumps Ca2+ from the cytosol back into the SR using the energy of ATP hydrolysis.