The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and membranes of the membrane-bound organelles in the cell. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed and prevents them from diffusing into areas where they should not be. Lipid bilayers are ideally suited to this role, even though they are only a few nanometers in width, because they are impermeable to most water-soluble (hydrophilic) molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations and pH by transporting ions across their membranes using proteins called ion pumps.
Erwin Neher is a German biophysicist, specializing in the field of cell physiology. For significant contribution in the field, in 1991 he was awarded, along with Bert Sakmann, the Nobel Prize in Physiology or Medicine for "their discoveries concerning the function of single ion channels in cells".
The plasma membranes of cells contain combinations of glycosphingolipids, cholesterol and protein receptors organised in glycolipoprotein lipid microdomains termed lipid rafts. Their existence in cellular membranes remains controversial. Indeed, Kervin and Overduin imply that lipid rafts are misconstrued protein islands, which they propose form through a proteolipid code. Nonetheless, it has been proposed that they are specialized membrane microdomains which compartmentalize cellular processes by serving as organising centers for the assembly of signaling molecules, allowing a closer interaction of protein receptors and their effectors to promote kinetically favorable interactions necessary for the signal transduction. Lipid rafts influence membrane fluidity and membrane protein trafficking, thereby regulating neurotransmission and receptor trafficking. Lipid rafts are more ordered and tightly packed than the surrounding bilayer, but float freely within the membrane bilayer. Although more common in the cell membrane, lipid rafts have also been reported in other parts of the cell, such as the Golgi apparatus and lysosomes.
Roger David Kornberg is an American biochemist and professor of structural biology at Stanford University School of Medicine. Kornberg was awarded the Nobel Prize in Chemistry in 2006 for his studies of the process by which genetic information from DNA is copied to RNA, "the molecular basis of eukaryotic transcription."
Erich Sackmann was a German experimental physicist and a pioneer of biophysics in Europe.
Single-particle tracking (SPT) is the observation of the motion of individual particles within a medium. The coordinates time series, which can be either in two dimensions (x, y) or in three dimensions (x, y, z), is referred to as a trajectory. The trajectory is typically analyzed using statistical methods to extract information about the underlying dynamics of the particle. These dynamics can reveal information about the type of transport being observed (e.g., thermal or active), the medium where the particle is moving, and interactions with other particles. In the case of random motion, trajectory analysis can be used to measure the diffusion coefficient.
One property of a lipid bilayer is the relative mobility (fluidity) of the individual lipid molecules and how this mobility changes with temperature. This response is known as the phase behavior of the bilayer. Broadly, at a given temperature a lipid bilayer can exist in either a liquid or a solid phase. The solid phase is commonly referred to as a “gel” phase. All lipids have a characteristic temperature at which they undergo a transition (melt) from the gel to liquid phase. In both phases the lipid molecules are constrained to the two dimensional plane of the membrane, but in liquid phase bilayers the molecules diffuse freely within this plane. Thus, in a liquid bilayer a given lipid will rapidly exchange locations with its neighbor millions of times a second and will, through the process of a random walk, migrate over long distances.
A model lipid bilayer is any bilayer assembled in vitro, as opposed to the bilayer of natural cell membranes or covering various sub-cellular structures like the nucleus. They are used to study the fundamental properties of biological membranes in a simplified and well-controlled environment, and increasingly in bottom-up synthetic biology for the construction of artificial cells. A model bilayer can be made with either synthetic or natural lipids. The simplest model systems contain only a single pure synthetic lipid. More physiologically relevant model bilayers can be made with mixtures of several synthetic or natural lipids.
David R. Nelson is an American physicist, and Arthur K. Solomon Professor of Biophysics, at Harvard University.
Laurdan is an organic compound which is used as a fluorescent dye when applied to fluorescence microscopy. It is used to investigate membrane qualities of the phospholipid bilayers of cell membranes. One of its most important characteristics is its sensitivity to membrane phase transitions as well as other alterations to membrane fluidity such as the penetration of water.
Joachim Heinrich Seelig is a German physical chemist and specialist in NMR Spectroscopy. He is one of the founding fathers of the Biozentrum of the University of Basel. He reached emeritus status in 2012.
Tobias C. Walther is the chair of the cell biology program at Sloan Kettering Institute in New York City and a professor at Weill Cornell School of Medicine, where he co-directs the Farese and Walther lab. He has been a Howard Hughes Medical Institute investigator since 2015. His primary responsibilities are to provide leadership in research and teaching in the scientific fields of metabolism, membrane biology and lipids.
Stephen H. White is an American Biophysicist, academic, and author. He is a Professor Emeritus of Physiology and Biophysics at the University of California, Irvine.
Volker Haucke is a biochemist and cell biologist. He is Director of the Leibniz-Forschungsinstitut für Molekulare Pharmakologie Berlin (FMP) Berlin and Professor of Molecular Pharmacology at the Institute for Pharmacy of the Free University of Berlin.
Amy S. Gladfelter is an American quantitative cell biologist who is interested in understanding fundamental mechanisms of cell organization. She was a Professor of Biology and the Associate Chair for Diversity Initiatives at the University of North Carolina at Chapel Hill, before moving to Department of Cell Biology at Duke University. She investigates cell cycle control and the septin cytoskeleton. She is also affiliated with the Lineberger Comprehensive Cancer Center and is a fellow of the Marine Biological Laboratory in Woods Hole, MA.
In biochemistry, biomolecular condensates are a class of membrane-less organelles and organelle subdomains, which carry out specialized functions within the cell. Unlike many organelles, biomolecular condensate composition is not controlled by a bounding membrane. Instead, condensates can form and maintain organization through a range of different processes, the most well-known of which is phase separation of proteins, RNA and other biopolymers into either colloidal emulsions, gels, liquid crystals, solid crystals or aggregates within cells.
Sarah Louise Veatch is an American biophysicist, associate professor of biophysics at University of Michigan.
Karen Renee Gibson Fleming is a Professor of Biophysics at Johns Hopkins University. She investigates the energetics of transmembrane helix-helix interactions. Fleming was awarded the 2020 Protein Society Carl Brändén Award.
Michael Schick is a physicist and an academic. He is a professor emeritus at the University of Washington.
Enrico Gratton is an Italian-American biophysicist. His research is focused on the field of biophotonics and fluorescence spectroscopy.
