Each amino acid has a core alpha carbon atom (Cα), and attached to that is a single hydrogen atom, a carboxyl group (-COOH), and an amino group (-NH2). Amino AcidsĪmino acids are the building blocks of protein structures in the body and are each made up of several molecular groups. As hydrophilic molecules dissolve in water and are polar, hydrophobic ones will only dissolve in oil and are nonpolar. Oil will float to the top, and water will pool on the bottom. Examples of hydrophobic molecules are oils, fats, and lipids that will not dissolve in water.Įlementary science: put some colorful oil and water into one clear bottle, shake up it like crazy, and then watch as the oil and water slowly return to their own sides of the bottle. Water is not impossible to resist, however: hydrophobic molecules resist water, repel it even, or as the name suggests, they are phobic or "fearful" of water. Sugar and salt are examples of hydrophilic substances, but even the Titanic, 2 miles down at the bottom of the ocean, is slowly dissolving in water and corroding away. Hydrophilic molecules can bind with water, and thus they make up substances that can dissolve in water. Hydrophilic means "water loving," and hydrophilic molecules are receptive to water and are likewise in the polar group of molecules. With the majority of the electrons always resting on oxygen's side of the bonded H20 molecule, water is a polar molecule, and oxygen holds the negative side of the bond, while the hydrogens hold a positive charge. Now oxygen has all eight of its electron spots filled. Water is a polar molecule because H2O means there's two hydrogen atoms that can then form hydrogen bonds attached to the one stronger oxygen atom: oxygen has six electrons of its own, but it can hold onto eight, and so when two unsuspecting hydrogen atoms come along, each of them having just one electron to call their own, oxygen gathers them close and insists that they share.
That makes the molecule polar: one end is positive, with fewer electrons, and the other end is negative, hogging as many electrons as possible. One atom will be stronger and will pull negative electrons away from the other atom. Polar molecules are what form when two atoms from different elements come together to make an uneven compound. hydrophobic molecules, and the amino acids. We'll start with the basics: polar molecules, hydrophilic vs. Mechanisms of membrane fusion disparate players and common principles is a review paper.You may have run across this term and wondered what it meant-what are hydrophilic amino acids and what do they do? Hope you feel like brushing up on some basic organic chemistry, because this article's aim is to shed some light on the subject, and give you a quick chemistry refresher course on these important structures and molecules in our bodies. A virus with hydrophobic residues that are always ready-to-go, in comparison, would likely fuse with a lot of random/off-target membranes of cells or vesicles that would not be permissive to viral replication. This works to the advantage of the virus, since if the spike is close enough to be cleaved by TMPRSS2, it's close enough to stab the membrane of the correct cell. The cleavage of spike is crucial to initiate this process because the hydrophobic residues are not accessible/cannot interact with the cell membrane unless the spike has been cleaved. Here's a model of protein-mediated fusion from that same review (they emphasize that the deformation is key): The hydrophobic residues are key because they are what enables the other end of the spike protein to interact with and deform the cell membrane. Essentially, the spike makes this process thermodynamically favorable. (a) shows a model of two lipid bilayers fusing (minus protein contributions). A useful review focusing on the bilayer side that I'll reference throughout this answer is here: Mechanics of membrane fusion, doi: 10.1038/nsmb.1455. Interesting question! Yes, the hydrophobic amino acids are very important they facilitate interaction with the hydrophobic (inner) portion of the lipid bilayer.
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