Two different compounds A and B are checked for cell uptake capacity. Two differ

Question

Two different compounds A and B are checked for cell uptake capacity. Two different probes are used: One inside the cell (Probe 1) and the other outside the cell (Probe 2). The probes have the ability to measure the concentration of both A and B. Once the probes are located in the correct place, increased amounts of compounds (A and B) are added to the medium. A plot of intracellular concentration vs intracellular concentration (for both A and B) is displayed 1) Which compound is passing through the membrane by just diffusion (passive process) and which compound does require a carrier Define the chemical properties of A and B Suppose that you perform the very same experiment using liposomes instead of cells. How the plot intracellular concentration vs intracellular concentration would look like. Justify your answer 2) 3) 2

Explanation / Answer

1) Compound A is passing cell membrane just by diffusion, while compound B requires a carrier. Diffusion is a process in which solute moves from higher to lower concentration. While in carrier mediated process it may move against concentration gradient with help of carrier protein. Since compound B is using a carrier protein, after a time saturation occurs which leads to less uptake.

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2) Compound A is non-polar and small in size, it may be gaseous form thus allowing easy diffusion. Hydrophobic compounds can easily pass through lipid bilayer

Compound B is relatively large in size and polar in nature, it may have some affinity for the carrier protein to which it binds. It is hydrophilic in nature which makes it difficult to pass through lipid bilayer.

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3) If we perform a similar experiment using liposome we would observe same plot for compound A, and a sharp decrease in the intracellular concentration of compound B.

This is because Liposomes are similar in structure to Cell membrane. They contain a lipid bilayer. This will allow the Compound A to easily enter the liposome.

But liposomes differ from Cell membrane in not having transport proteins. Due to this Compound B will have trouble entering the liposome.

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