The effects of temperature and lipid composition on membrane fluidity are often

Question

The effects of temperature and lipid composition on membrane fluidity are often studied by using artificial membranes containing only one or a few kinds of lipids and no proteins. Assume that you and your lab partner have made the following artificial membranes: acids. Membrane 2: Same as membrane 1 except that each of the 16-carbon fatty acids has a single cis double bond. only 14 carbon atoms. . Membrane 2: Same as membrane 1 except that each of the 16-carbon fatty acids has a single trans double bond. Rank these membranes based on their transition temperatures (starting from highest to lowest). Explain your reasoning.

Explanation / Answer

Transition temperature is the temperature at which there is a transition from ordered structure of fatty acid tails to unordered.
Chain length of fatty acids Tm
Degree of unsaturation 1/ Tm
Cis double bonds contributes to fluidity.

Based on this, the order for transition temperatures will be

Membrane 3 < Membrane 1 < Membrane 2 < Membrane 4

Membrane 3 has least transition temperature as transition temperature increases on increasing number of carbon in fatty acids but membrane 3 has least number of carbons (14) in all the four membranes.

Then comes the membrane 1, beacause it contains the same number of carbons as in membrane 2 and 4 but it does not unsaturation like membrane 2 and 4 which increases transition temperature.

Then comes membrane 2, because membrane 2 has single cis double bond which increases transition temperature but not as much as trans bond which is present in membrane 4.

So last comes the membrane 4 which has maximum transition temperature as it contains single trans double bond which increases its transition temperature.

The "U" shape of the cis isomer doesn't pack as well as the straighter shape of the trans isomer. The poorer packing in the cis isomersmeans that the intermolecular forces aren't as effective as they should be and so less energy is needed to melt the molecule - a lower melting point.

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