Passage
Although the structure of the cell membrane has been investigated repeatedly, few studies examine the contribution of its lipid components. Lipid composition influences the fluidity and permeability of cell membranes in the human body. Chronic diseases such as atherosclerosis and psoriasis arise from alterations to the lipid composition.Atherosclerosis is caused by the accumulation of cholesterol in the endothelial cells lining the arterial wall. Cholesterol carried by low-density lipoprotein (LDL) is deposited into cell membranes, where it forms cholesterol crystalline domains (CCDs) . In damaged cells, these CCDs increase membrane permeability and contribute to the formation of cholesterol plaques that can potentially block the artery itself.Omega-3 fatty acids (O3FAs) derived from marine animals may be used to slow the development of atherosclerosis. Formulations of O3FA contain varying concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Figure 1) . Present research suggests that formulations of O3FA should contain EPA exclusively because it prevents cholesterol from organizing into CCDs. Nonetheless, atherosclerosis is generally treated by administering drugs referred to as statins, which decrease the free cholesterol in blood plasma by inhibiting the production of a cholesterol precursor. Statin therapy combined with O3FAs may be used to reduce atherosclerosis in patients with persistent hypertriglyceridemia (high triglyceride plasma levels) .
Figure 1 Organization of membranes in endothelial and epidermal cellsWater loss from the uppermost layer of the epidermis, the stratum corneum (SC) , is prevented by specialized lipids called ceramides (cer) . Psoriasis is a skin disease in which the permeability of the SC is compromised due to a significant decrease in the level of ceramides. The scarcity of ceramides impedes the formation of a lipid matrix called the long periodicity phase (LPP) in the cell membrane. Increasing the concentration of ceramides such as esterified omega-hydroxyacyl-sphingosine (cer-EOS) has been shown to reduce the permeability of SC cell membranes and may be used to treat psoriasis scabs (Figure 1) .
Adapted from Mason RP, Jacob RF, Shrivastava S, Sherratt SC, Chattopadhyay A. Eicosapentaenoic acid reduces membrane fluidity, inhibits cholesterol domain formation, and normalizes bilayer width in atherosclerotic-like model membranes. Biochim Biophys Acta. 2016;1858(12) :3131-3140.
-What structural feature in the molecules shown in Figure 1 would result in the greatest increase in cell membrane fluidity?

Question

Passage
Although the structure of the cell membrane has been investigated repeatedly, few studies examine the contribution of its lipid components. Lipid composition influences the fluidity and permeability of cell membranes in the human body. Chronic diseases such as atherosclerosis and psoriasis arise from alterations to the lipid composition.Atherosclerosis is caused by the accumulation of cholesterol in the endothelial cells lining the arterial wall. Cholesterol carried by low-density lipoprotein (LDL) is deposited into cell membranes, where it forms cholesterol crystalline domains (CCDs) . In damaged cells, these CCDs increase membrane permeability and contribute to the formation of cholesterol plaques that can potentially block the artery itself.Omega-3 fatty acids (O3FAs) derived from marine animals may be used to slow the development of atherosclerosis. Formulations of O3FA contain varying concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Figure 1) . Present research suggests that formulations of O3FA should contain EPA exclusively because it prevents cholesterol from organizing into CCDs. Nonetheless, atherosclerosis is generally treated by administering drugs referred to as statins, which decrease the free cholesterol in blood plasma by inhibiting the production of a cholesterol precursor. Statin therapy combined with O3FAs may be used to reduce atherosclerosis in patients with persistent hypertriglyceridemia (high triglyceride plasma levels) .

Figure 1 Organization of membranes in endothelial and epidermal cellsWater loss from the uppermost layer of the epidermis, the stratum corneum (SC) , is prevented by specialized lipids called ceramides (cer) . Psoriasis is a skin disease in which the permeability of the SC is compromised due to a significant decrease in the level of ceramides. The scarcity of ceramides impedes the formation of a lipid matrix called the long periodicity phase (LPP) in the cell membrane. Increasing the concentration of ceramides such as esterified omega-hydroxyacyl-sphingosine (cer-EOS) has been shown to reduce the permeability of SC cell membranes and may be used to treat psoriasis scabs (Figure 1) .
Adapted from Mason RP, Jacob RF, Shrivastava S, Sherratt SC, Chattopadhyay A. Eicosapentaenoic acid reduces membrane fluidity, inhibits cholesterol domain formation, and normalizes bilayer width in atherosclerotic-like model membranes. Biochim Biophys Acta. 2016;1858(12) :3131-3140.
-What structural feature in the molecules shown in Figure 1 would result in the greatest increase in cell membrane fluidity?

Quizplus · Accepted Answer

11ecba2d_0e16_ea6b_a3bf_6d7b27970300_MD0008_00 Fatty acids are nonpolar molecules composed of straight hydrocarbon chains with carboxyl groups at one end. Humans synthesize fatty acids with an even number of carbon atoms, and chains usually range from 14 to 18 carbon atoms long. Fatty acids with no carbon-carbon double bonds are described as saturated because each carbon atom has the maximum number of hydrogen atoms possible. In contrast, an unsaturated fatty acid contains one (monounsaturated) or multiple (polyunsaturated) double bonds that may be in either the cis (Z) or the trans (E) configuration. Unsaturation contributes significantly to membrane fluidity. The carbon-carbon double bonds decrease the melting temperature of fatty acid chains and increase the average space between lipids. As a result, lipids with unsaturated fatty acid chains remain liquid (fluid) at room temperature. The cis configuration is particularly important in cell membranes as it introduces a bend or "kink" in the fatty acid that prevents phospholipids from stacking together and solidifying. The passage introduces various molecules that have different effects on membrane fluidity. Of the choices listed, the cis bond of the polyunsaturated fatty acid EPA contributes the most to membrane fluidity. (Choice B) The trans bond in cer-EOS does not increase the membrane fluidity significantly as it does not disrupt the straight shape of the fatty acid chain. (Choices C and D) The carboxyl groups of free fatty acids such as DHA and the phosphate groups of phospholipids do not contribute to membrane fluidity. They are hydrophilic (polar) regions that associate with the aqueous sides of the cell membrane bilayer. Educational objective: Saturated fatty acids have no carbon-carbon double bonds and therefore stack closely in the cell membrane. Unsaturated fatty acids have one or more double bonds in either the cis or the trans configuration. In particular, the cis configuration enhances membrane fluidity by introducing a bend or "kink" in the fatty acid chain.