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Science and innovation of the republic of uzbekistan urgench state university
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| bet | 12/13 | | Sana | 16.05.2024 | | Hajmi | 1,48 Mb. | | #237391 |
Bog'liq Structure and function of biological membranes.Chapter III. Conclusion
All membranes in the cell share some common features, despite the fact that they each have a different composition, fluidity, and permeability. In this topic, we will discuss the common features of all membranes and touch briefly on which macromolecules contribute to specific membrane functions.
It’s worth noting that a biological membrane is not the same thing as a phospholipid bilayer, despite the fact that these terms sometimes are used interchangeably. A phospholipid bilayer is made only of phospholipids and nothing else, whereas a biological membrane will have many types of lipids in it (including glycolipids and cholesterol) as well as proteins. We’ll see examples of this later in the topic. One of the most basic features of cells is that they are separated from the environment by a membrane. Not only do the membranes create a barrier that separates the inside of the cell from the exterior, but they also function in a way that gives the cell a great deal of control over what can enter or exit it. This creates an environment inside the cell that is different from the outside Molecules are able to move around freely (diffuse) within each cellular compartment. However, it is more challenging for some molecules to cross membranes. This is because biological membranes have specific chemical properties, which determine when and how molecules cross the membrane. Thus, membranes are a key feature that allows cells to maintain compartments with a distinctive chemical composition.
Like everything in science, the idea that biological membranes contain both lipids and proteins took time for cell biologists to accept. Sometime in the 1970s, the current concept of the membrane was developed and was known as the “fluid mosaic model.” The “fluid” part refers to the lipids being able to move around within the layers of the membrane, and the “mosaic” part refers to the fact that proteins are expected to be scattered across and throughout the membrane.
When phospholipids are mixed with water, they will spontaneously form into spherical bodies called liposomes that have water on the inside as well as on the outside (Figure 02-02B). Liposomes are commonly used for the targeted oral delivery of drugs and other agents in medical treatment. Liposomes are the simplest version of a cell membrane, so they are able to fuse with a real cell membrane to release its contents directly into the cell. This is useful if the compound inside the liposome would not easily pass through a membrane under normal circumstances. A great example of this technology in action is the RNA vaccines developed to target the SARS-CoV-2 virus (the cause of the COVID-19 pandemic). These RNA vaccines use an outer coating called a lipid nanoparticle, which is a combination of phospholipids, cholesterol, and other compounds that are designed to help contain and stabilize the RNA vaccine and ease its entry into the cell.
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