humpf!!
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A series of experiments are performed to determine the mechinism by which a pharmacological agent traverses cell membranes and accumulates within target cells. The rate of transport depends on the concentration of the drug only. When the extracellular concentration of the agent exceeds 10mM, no further increase in the rate of uptake is observed. Structurally similar compounds pass thru the cell membrane, but at a lower rate. Ouabain, an inhibitor of N/K ATPase, fails to inhibit transport. Which of the following is the mechinism by which this agent enters the cell.
a) antiport
b) facilitated diffusion
c) ion-gated coupling
d) simple diffusion
e) symport
(I think "D")
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| robin082006
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B
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| disha
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i think its d.robins plz explain your answer,maybe im wrong.
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| Slacker
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B. Because the substance is being transported by a protein. At first the rate of transport will increase if the amount of substance is increased. But once all the protein transportors are saturated(Tm is reached), the rate of transport can't be increase by increasing the amount of substance.
It can't be simple diffusion because that doesn't require protein transportors and i guess the rate of transport will always increase with the concentration gradient.
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| yuwa
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my question for slacker:
Is it possible that the concentration gradient will get a balance between intracellualr and extracellular, even adding more drug, no more transportation.
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| Slacker
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well facilated diffusion pushes substance down the gradient, so yea, i guess if the concentration gradient is balanced between the intracelluar and extracellular comparments then transportation should stop. what do u think?? anyone else???
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| robin082006
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Slacker:
in simple diffusion: transportation stops when intracellular concentration and extracellular concentration are balanced.
But in faciliated: it may not stop and depends on the requirement and activity of cells
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| Slacker
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But doesn't facilitated diffusion works by concentration gradient???
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| robin082006
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Maybe I'm wrong Slacker, I know that faciliated transport is down the gradient but I do not see Kaplan say it stops when intracellular and extracellular concentration are balanced.
You're right, it stops.
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| robin082006
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Maybe I'm wrong Slacker, I know that faciliated transport is down the gradient but I do not see Kaplan say it stops when intracellular and extracellular concentration are balanced.
You're right, it stops.
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| Musuq
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the difference would be here
"Structurally similar compounds pass thru the cell membrane, but at a lower rate."
because there is not the same dynamic of diffusion, think about facilitated because in simple diff the dynamics have no difference at all. i would go with facilitated, no doubts.
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| suv
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facilitated diffusion is saturable where as simple diffusion is not
so it is facilitated diffusion
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| Musuq
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both diffusion are driven by conecntration gradient so, you can have a doubt once the gradient is at equilibrium, that's what I saw lines upward so I checked the notes and doctor dunn said if there is doubts about which one is, see the dynamic of transport because in simple diff there is no difference in the dynamic of different molecules, while in facilitated there is since it is specific.
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| yuwa
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Musuq, Very good explanation. Thanks.
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