Continuing with the study of cell biology, is the eighth universal feature of all cells, according to Alberts et al.:
The point here is very straightforward. Plasma membranes surround all cells, and serve as selective barriers allowing a cell to concentrate the nutrients that is has gathered from its environment, retain the products synthesized by the cell for its own use, and also allows the cell to excrete waste products. All in all, plasma membranes maintain the integrity of the cell as a chemical system that is coordinated (Alberts et al. 2014).
It is important to know also what makes up a plasma membrane. Particular molecules arrange themselves in a particular way to make a plasma membrane, and understanding their arrangement can tell you more about the properties of a plasma membrane. Firstly, the molecules making up a plasma membrane are amphiphilic, which means that they consist of two parts, with one of them being hydrophobic or water-insoluble, and the other being hydrophilic, or water-soluble. When placed in water, the molecules take up a position with hydrophobic portions making contact with one another, allowing them to hide from the water. Predictably, then, the hydrophilic portions of the molecules are exposed and are not “afraid” of the water. Molecules that are amphiphilic, such as those in this specific case, aggregate in a particular way in water, causing the creation of a bilayer, which then forms small closed vesicles. The molecules that are a part of the process described above are phospholipid molecules (Alberts et al. 2014). Below, you can see what a phospholipid bilayer as described looks like.
It should be noted that without regards to slight variation in chemical details, hydrophobic tails of the predominant membrane molecules in all cells are hydrocarbon polymers. The process described above is evidence of an important principle of cells, which is that molecules produced by a cell self-assemble in order to achieve structures that the cell requires (Alberts et al. 2014).
Going back to the original point, plasma membranes allow materials to be imported into the cell and exported out of the cell in accordance with the cell’s needs. This means that the cell is permeable to some degree. Cells, for this reason, have specialized proteins embedded in their membrane, known as membrane transport proteins. These proteins are by and large the major determinants of the molecules that are permitted to enter the cell. Catalytic proteins inside of the cell thus are tasked with determining the reactions that the particular molecules undergo. Thus, it can be said that when a cell manufactures specific proteins, genetic information is recorded in the DNA sequence, and this then dictates the entirety of the chemistry that occurs within the cell. More than just the chemistry, the form and behavior of the cell is also dictated in this way (Alberts et al. 2014).
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