Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?

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Membrane lipids: where they are and how they behave.

Molecular Anatomy of a Trafficking Organelle

Membrane curvature is no longer seen as a passive consequence of cellular activity but an active means to create membrane domains and to organize centres for membrane trafficking. Curvature can be dynamically modulated by changes in lipid composition, the oligomerization of curvature scaffolding proteins and the reversible insertion of protein regions that act like wedges in membranes. There is an interplay between curvature-generating and curvature-sensing proteins during vesicle budding. This is seen during vesicle budding and in the formation of microenvironments. On a larger scale, membrane curvature is a prime player in growth, division and movement.

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Membrane curvature and mechanisms of dynamic cell membrane remodelling

This critical review gives a short overview of the widespread use of gold nanoparticles in biology. We have identified four classes of applications in which gold nanoparticles have been used so far: labelling, delivering, heating, and sensing. For each of these applications the underlying mechanisms and concepts, the specific features of the gold nanoparticles needed for this application, as well as several examples are described (142 references).

Biological applications of gold nanoparticles

Cellular plasma membranes are laterally heterogeneous, featuring a variety of distinct subcompartments that differ in their biophysical properties and composition. A large number of studies have focused on understanding the basis for this heterogeneity and its physiological relevance. The membrane raft hypothesis formalized a physicochemical principle for a subtype of such lateral membrane heterogeneity, in which the preferential associations between cholesterol and saturated lipids drive the formation of relatively packed (or ordered) membrane domains that selectively recruit certain lipids and proteins. Recent studies have yielded new insights into this mechanism and its relevance in vivo, owing primarily to the development of improved biochemical and biophysical technologies.

The mystery of membrane organization: composition, regulation and roles of lipid rafts

Recent advancements in single-molecule tracking methods with nanometer-level precision now allow researchers to observe the movement, recruitment, and activation of single molecules in the plasma membrane in living cells. In particular, on the basis of the observations by high-speed single-particle tracking at a frame rate of 40,000 frames s(1), the partitioning of the fluid plasma membrane into submicron compartments throughout the cell membrane and the hop diffusion of virtually all the molecules have been proposed. This could explain why the diffusion coefficients in the plasma membrane are considerably smaller than those in artificial membranes, and why the diffusion coefficient is reduced upon molecular complex formation (oligomerization-induced trapping). In this review, we first describe the high-speed single-molecule tracking methods, and then we critically review a new model of a partitioned fluid plasma membrane and the involvement of the actin-based membrane-skeleton "fences" and anchored-transmembrane protein "pickets" in the formation of compartment boundaries.

Paradigm Shift of the Plasma Membrane Concept from the Two-Dimensional Continuum Fluid to the Partitioned Fluid: High-Speed Single-Molecule Tracking of Membrane Molecules

Detection of Non-Brownian Diffusion in the Cell Membrane in Single Molecule Tracking

Protein–Lipid Interactions in the Formation of Raft Microdomains in Biological Membranes

There is an urgent need to examine the risk of infection from aerosols generated during dental treatment and to review infection control. However, existing research on aerosol particles associated with dental treatment is by no means sufficient, and little research has been done on the details of aerosol particle generation in the clinical environment, the mechanisms, and patterns of distribution in open and closed spaces, the time they are suspended in the air, the amount and size of particles present. Therefore, to minimize the influence of background particles, laser beams, a high-sensitivity camera, and a particle counter were used in a large super-clean laboratory (SCL) to investigate the dynamics of aerosols generated during dental micromotor operation. The large number of aerosol particles generated by the use of the micro-engine rose rapidly within 30 seconds and were suspended in the room atmosphere. Within a 100 cm radius of the user, the scattering peaked at about 90 seconds. The particles were further diffused into the room with the passage of time, reaching a maximum at 210 seconds and gradually decreasing thereafter, confirming that the 4 x 4 m room had returned to equilibrium. The experiment was conducted under sealed conditions in the SCL without the use of any suction device inside or outside the oral cavity. Although the conditions did not faithfully reproduce the actual conditions in a dental clinic, we were able to obtain groundbreaking results that demonstrated for the first time the scattering of fine particles, eliminating various possible complications in the background. At present, our knowledge of the infectivity of COVID-19 from patients' oral cavity and saliva is still insufficient, and further studies and information are needed. 

Junko Kondo

Papers

Paradigm Shift of the Plasma Membrane Concept from the Two-Dimensional Continuum Fluid to the Partitioned Fluid: High-Speed Single-Molecule Tracking of Membrane Molecules

Detection of Non-Brownian Diffusion in the Cell Membrane in Single Molecule Tracking

Protein–Lipid Interactions in the Formation of Raft Microdomains in Biological Membranes

A study both to measure and to visualize the scattering of fine particles generated during dental treatment