Phospholipids, a class of amphiphilic molecules, are the main components of biological membranes. The amphiphilic nature of these molecules defines the way in which they form membranes. They arrange themselves into lipid bilayers, by forming a sheet composed of two layers of lipids. Each layer forms by positioning their lypophilic chains to the same side of the layer. The two layers then stack such that their lyphphilic chains touch on the inside and their polar groups are outside facing the surrounding aqueous media. Thus the inside of the bilayer sheet is a non-polar region sandwiched between the two polar sheets.
Although phospholipids are the principal constituents of biological membranes, there are other constituents, such as cholesterol and glycolipids, which are also included in these structures and give them different physical and biological properties.
Many other amphiphilic compounds, such as pepducins, strongly interact with biological membranes by insertion of the hydrophobic part into the lipid membrane, while exposing the hydrophilic part to the aqueous medium, altering their physical behavior and sometimes disrupting them.
Aβ proteins form antiparallel β sheets which are strongly amphiphilic, and which aggregate to form toxic oxidative Aβ fibrils. Aβ fibrils themselves are composed of amphiphilic 13-mer modular β sandwiches separated by reverse turns. Hydropathic waves optimize the description of the small (40,42 aa) plaque-forming (aggregative) Aβ fragments.
Antimicrobial peptides (AMPs) are another class of amphiphilic molecules, a big data analysis showed that amphipathicity best distinguished between AMPs with and without anti-gram-negative bacteria activities. The higher amphipathicity, the better chances for AMPs possessing antibacterial and antifungal dual activities.