You have generated synthetic membranes in the laboratory. The properties of the

Question

You have generated synthetic membranes in the laboratory. The properties of the membranes are listed below. Membrane 1: Made entirely from phospholipids with saturated 16-carbon fatty acids Membrane 2:Made entirely from phospholipids containing 16-carbon fatty acids with three double bonds Membrane 3: Made entirely from phospholipids containing 16-carbon fatty acids with one double bond a. Based on what you know about membrane fluidity, assign each membrane to the corresponding transition temperature below. At temperatures above the transition temperature a cell membrane becomes too fluid for the cell to survive. Transition Temperature 2° C 20°C 42°C b. Which membrane would allow a cell to survive best in a human? Explain. List three ways that an organism with the 42°C transition temperature could modify its membrane to survive in a 1° C lake? c.

Explanation / Answer

Biological membranes are mainly composed of lipids and proteins (protein molecules float in the sea of lipids) and provide selective permeability for various molecules into the cell. They are a sheet-ike, non-covalent assemblies. The lipid molecules of the membrane prevent the free flow of polar molecules whereas proteins serve as receptors for signaling cascades and components of transport systems. Membrane structure and composition is dynamic i.e., it changes according to the environmental conditions. They are asymmetric and fluid in nature i.e., all the lipids and several proteins can easily diffuse rapidly in the plane of the membrane.

a.
2'C = Membrane 2
20'C = Membrane 3
42'C = Membrane 1

b. Membrane 1 has a transition temperature in the range of 42'C. SO, it remains in less-fluid state at room temperature.

c. The fluidity of the membrane depends on its chemical composition and temperature. Lipids with longer fatty acid chains have more interactions between the hydrophobic fatty acid tails, stabilizing the crystal-like state and making the membrane less fluid. Saturated fatty acids also strengthen membranes and reduce fluidity.

The shift to the lower temperature (1'C lake) would decrease the fluidity of the membrane by increasing the packing of the hydrophobic chains. To prevent this, new phospholipids would be synthesized having shorter chains and more number of double bonds. The shorter chains would decrease the amount of Vander Waals interactions and presence of double bonds increases the kink in structure, would reduce the packing of the fatty acid tails of the phospholipids.

Incorporation of specific lipids, such as sphingomyelin is known reduce the membrane fluidity. So, its synthesis/incorporation may go down.

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