4. Permeability Testing You perform a permeability lab where you tested the perm

Question

4. Permeability Testing You perform a permeability lab where you tested the permeability of various molecules in two different systems. System 1 contains artificial liposomes, as described in Section 6.2 of your text. The liposomes in this system are created with phospholipids only System 2 is a simple cell culture You determine the time is takes for each the molecules (V-Z) to pass through both the liposome and cell membrane. You placed your results in the table below, where 5 represents the fastest transit time, and 1 represents the slowest transit time Transport/Permeability Transport/Permeability in Artificial Liposomes in Cell Molecule Properties Small, non-polar uncharged Water Medium, polar Uncharged Small, polar uncharged Large, charged 4 4 a. Explain (in the context of membrane permeability) why molecule V moves the fastest through both membranes, and why molecule Z moves the slowest. 3 pts b. Explain one possible reason for why molecule W (water), passes through the membrane relatively quickly in the cell model, but passes relatively slowly in the artificial liposome system. 3 pts 5. Too Much Water Background: On the morning of January 12, 2007, a Sacramento, CA radio station held a "Hold Your Wee for a Wi" contest. The radio station, KDND, promised to give the highly-sought Wii game system to the winner of their contest. Contestants were asked to drink as much water as they could without urinating. The contestant able to hold the most water would be named the winner. One of the contestants, Jennifer Strange, 28 consumed nearly two gallons of water in three hours time. She died shortly after taking part in the contest. a. Discuss how an excessive increase in water can affect a person's cells, making sure to include tonicity and osmosis as part of your discussion. 3 pts b. Speculate how the changes you describe in part a could potentially lead to death

Explanation / Answer

4. Characteristics of membranes:

i. Composed of the lipid bilayer (Lipids + proteins)

ii. Selectively permeable

iii. Fluid like (Dynamic in structure).

a. The movement of a molecule through a membrane depends upon its size and charge properties. Since membranes are composed of hydrophobic lipid molecules, they allow free passage of small non-polar molecules. They do not allow the passage of charged/polar/large molecules.

Since V is a small, non-polar molecule, it can freely diffuse through the membrane.

Since W is a large, charged molecule, it moves slowly through the membrane.

b. Liposomes are artificial membranes. They are composed only of lipid molecules. On the other hand, biological membranes contain several proteins which serve as carriers for polar substances like water molecules. Hence, biological membranes show greater permeability to water than artificial liposomes.

5.

a. The cells in our body contain several solutes derived from metabolism. Compared to water, the cytoplasm is hypertonic in nature. When a human cell is placed in pure water, water moves into the cell leading to its bursting.

Water moves from high water potential to low water potential.

Water moves from hypotonic solution to hypertonic solution.

Pure water has maximum water potential i.e. = 0.

Water potential of any solution = Negative.

Greater the concentration of a solution, more negative is its water potential.

b. When Jennifer drank too much water, her body cells are exposed to the hypotonic condition. Generally, excess water in the body is excreted through urine and sweat. But, she forced not to urinate. So, her body cells were exposed to hypotonic condition for a long duration. This lead to bulging and bursting of cells causing irreversible damage. When a large number of cells break open, the whole body system becomes unbalanced eventually leading to death.

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