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.
-Structural lipids in the cell membrane can be derived directly from dietary sources or from lipase-mediated catabolism. Which statement correctly describes lipid processing during digestion?

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.
-Structural lipids in the cell membrane can be derived directly from dietary sources or from lipase-mediated catabolism. Which statement correctly describes lipid processing during digestion?

Quizplus · Accepted Answer

11ecba2d_0e1d_04ef_a3bf_7351b02ccbfc_MD0008_00 Lipid processing begins in the small intestine (duodenum), where bile salts break down lipid globules into smaller droplets in a process called emulsification. This process results in the formation of spherical structures, known as micelles, composed of a hydrophobic core containing the nonpolar hydrocarbon tails of lipids and an outer shell of polar head groups that make contact with water. The formation of micelles increases the surface area of lipid available for hydrolysis by lipases. Lipases are enzymes that digest certain emulsified lipids to facilitate their absorption, although some lipids are nonhydrolyzable. Hydrolyzable lipids contain ester bonds that can be cleaved by lipases through the addition of a water molecule (hydrolysis). These lipids include triacylglycerols, phospholipids, sphingolipids, and waxes. Nonhydrolyzable lipids do not contain the ester linkages necessary for lipase digestion. The most common nonhydrolyzable dietary lipids are cholesterol (steroids) and fat-soluble vitamins (A, D, E, and K). The question states that some dietary lipids are catabolized (broken down) by lipases, whereas others can be absorbed directly. The most accurate description of lipid processing acknowledges that all lipids are emulsified during digestion but only some lipids, including triglycerides and phospholipids, contain hydrolyzable ester bonds. (Choice A) Waxes are hydrolyzable lipids that consist of fatty acid chains bound to long-chain alcohols by an ester bond. (Choices B and C) All lipids are emulsified in the aqueous environment of the small intestine. Prostaglandins are nonhydrolyzable lipids that function as signaling molecules in the human body. Educational objective: Emulsification increases the surface area of lipids by breaking down large globules into spherical structures called micelles. Micelles have a hydrophobic core, which contains the nonpolar hydrocarbon tails of lipids, and an outer shell of polar head groups, which make contact with water. Lipases can cleave the ester bonds in hydrolyzable lipids such as triglycerides, phospholipids, and waxes by adding a water molecule (hydrolysis).