As organelle coverings, they allow the cell organelles to maintain their identity, internal environment and functional individuality. Finally, some proteins are very lightly attached to the membrane, with only a short lipid tail inserted into the hydrophobic region. [12]. The image also shows the anchoring of the membrane to the cytoskeleton. Cholesterol and proteins are embedded in the bilayer that gives the membrane a mosaic look. T for K+ is greater than 95%, and T for the remaining ions is less than 5%. An interesting future area for oligomerization studies is the transient association of receptors and membrane components in lipid rafts. Digoxin inhibits the activity of the Na+/K+-ATPase, resulting in an increase in intracellular Na+ and a decrease in intracellular K+. Since its original proposal, the concept of membrane microdomains has been better characterized at the molecular level. This arrangement gives the overall molecule an area described as its head (the phosphate-containing group), which has a polar character or negative charge, and an area called the tail (the fatty acids), which has no charge. Diffusion of glucose and other large polar molecules is impeded by the plasma membrane, and cellular uptake of glucose requires specific transport proteins. Although lipid phase separations in membranes were starting to achieve acceptance, their biological relevance awaited a link to a biological function. For comparison, human red blood cells, visible via light microscopy, are approximately 8 µm wide, or approximately 1,000 times wider than a plasma membrane. In computer simulations, the electron density profile can be calculated on the basis of the atomic number and the so-called partial charges for all heavy atoms (i.e., C, O, N, and P). These dynamic features in the trans-bilayer direction can be averaged for the collective behavior of many lipid molecules and plotted as the averaged electron density profiles of various lipid groups and segments. Glucose exits the cell on the basolateral surface by facilitated diffusion. Unsaturated fats are chains of carbon atoms that have double bonds between some of the carbons. Cell membranes are formed of many hundreds of phospholipids and each of them is made of different fatty acid side chains. (Adapted with permission from Zubrzycki, Xu et al. This is why it is called fluid mosaic model. Figure 3.5 depicts a snapshot of a fully hydrated ternary membrane patch composed of a 3:1:1 ratio of … Since the integral proteins are present within the lipid bilayer, their extraction is not possible. The term detergent-insoluble microdomains is more encompassing of its heterogeneity in composition than lipid rafts, as some of these microdomains may be selectively enriched for other phospholipids. This was verified by extracting cell membranes and spreading the lipids into a single layer. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org.