What type of barrier is produced by the phospholipids

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In fact, phospholipids heated in an aqueous solution tend to spontaneously form small spheres or droplets called micelles or liposomes , with their hydrophilic heads forming the exterior and their hydrophobic tails on the inside Figure 3.

Figure 3. In an aqueous solution, phospholipids tend to arrange themselves with their polar heads facing outward and their hydrophobic tails facing inward. Improve this page Learn More. Skip to main content. Module 5: Cell Membranes. Search for:. Phospholipids Learning Outcomes Explain why hydrophilic substances cannot pass through the interior of the cell membrane. The outer membrane of mitochondria and chloroplasts has pores that allow small molecules to pass easily. The inner membrane is loaded with the proteins that make up the electron transport chain and help generate energy for the cell.

The double membrane enclosures of mitochondria and chloroplasts are similar to certain modern-day prokaryotes and are thought to reflect these organelles' evolutionary origins. This page appears in the following eBook. Aa Aa Aa. Cell Membranes. Figure 1: The lipid bilayer and the structure and composition of a glycerophospholipid molecule. A The plasma membrane of a cell is a bilayer of glycerophospholipid molecules.

Figure 2: The glycerophospholipid bilayer with embedded transmembrane proteins. What Do Membranes Do? Figure 3: Selective transport. Specialized proteins in the cell membrane regulate the concentration of specific molecules inside the cell.

Figure 4: Examples of the action of transmembrane proteins. Transporters carry a molecule such as glucose from one side of the plasma membrane to the other. How Diverse Are Cell Membranes? Membranes are made of lipids and proteins, and they serve a variety of barrier functions for cells and intracellular organelles. Membranes keep the outside "out" and the inside "in," allowing only certain molecules to cross and relaying messages via a chain of molecular events.

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Some, having carbohydrate or polysaccharide molecules attached to them, are complex glycoprotein and glycolipid macromolecules that play roles in recognition between cells and act as receptors for molecules such as hormones. The physical state of membranes is dynamic, and rarely static. For example, when a cell adds extra cholesterol to a membrane, this changes the fluidity and converts the membrane from a liquid-like state to a more viscous gel-like state.

Components may be added or taken away as the cell changes, grows or becomes a specialist, and the modern picture of the cell membrane is a dynamic one of constant change, movement, modification and adaptation. Figure legend:.