Undergraduate biochemistry course content typically covers four core topics: proteins, sugars, nucleic acids, and lipids, but laboratory projects featuring lipid membranes are relatively rare.  We report the development of two new laser light scattering investigations of lipid membranes appropriate for the upper-level biochemistry laboratory.  In aqueous solution, phospholipids self-assemble into closed concentric spherical membrane layers that comprise multilamellar liposomes; these serve as model systems for cell membrane behavior.  In the first project, the osmotic properties of liposomes are assessed using hyper- and hypoosmotic solutions with both ionic and polar covalent solutes.  Solute and water migration across the phospholipid membrane alters liposome size, which is tracked with laser light scattering as a function of time over several minutes.  Students investigate membrane permeability across a 96% distearoyl phosphatidyl choline (DSPC) / 4% dicetyl phosphate lipid mixture for various types and concentrations of solutes.  In the second project, students use laser light scattering to investigate phospholipid phase transitions in DSPC and related phosphatidyl cholines.  As temperature increases, the structure of the bilayer membrane changes from a well-organized �gel� phase to a less-organized �liquid crystal� phase.  Figure 1 shows the intensity of light transmitted through an aqueous liposome suspension as a function of temperature.  The phase transition Ttr corresponds to an increase in transmitted light; students may also identify the pre-transition behavior at a slightly lower temperature.

Laser light scattering investigations of membrane permeability and lipid phase transitions in the undergraduate biochemistry laboratory

248th National Meeting (2014)

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