Mohammad Ashrafuzzaman

Structure of Membranes

Amphipathic molecules adsorb themselves onto air–water or oil–water interfaces, such that their head groups are facing the water environment. They aggregate to form either spherical micelles or liquid crystalline structures. In general, amphipathic molecules can be anionic, cationic, non-ionic, or zwitterionic. The relative concentrations of these surfactants in an aqueous solution will affect the solution’s physical and chemical properties. At a specific value, called the critical micelle concentration, micelles containing 20–100 molecules are formed spontaneously in the solution, with the hydrophilic head groups exposed and the hydrophobic tails hidden inside the micelle. The principal driving force for micelle formation is entropic, due to a negative free energy change accompanying the liberation of water molecules from clathrates. When phospholipids are mixed in water, they form double-layered structures, since their hydrophilic ends are in contact with water while the hydrophobic ends face inwards touching each other.

Membrane-Related Diseases

Life starts with a single cell, but the cell is also where the origin of most pathological changes and disorders can be traced. Disease states can, in most cases, be linked to the abnormal functioning of specific organs. A living cell is the fundamental unit where most of these abnormalities happen and where they are initiated. That is why a cell is also the ultimate target for the action of most drugs. Cancer, Alzheimer’s disease, Parkinson’s disease, various infectious diseases, etc. originate in individual cellular compartments, including the membrane. This chapter will be dedicated to a better understanding of the membrane’s involvement in diseases, and disease treatment using drugs targeting cell membranes. Several examples will be used for illustration purposes. However, due to the book’s subject matter, we will concentrate on the scientific aspects of a few of the membrane-based diseases, leaving the medical issues aside. Below, we list several diseases that are either directly or indirectly related to membrane properties and their abnormalities.

Ion Channels in Cancer

Ion channels in a cell are responsible for most of the cellular transport mechanisms. They play crucial roles in determination of cell membrane structure and cell function. In cancer condition, different ion channels play various kinds of critical roles in regard to cell proliferation, malignant angiogenesis, migration, and metastasis. The perturbed physiology of the cancer cell may regulate ion channel structures, energetics, and functions.

General Introduction and Nanoscale View of the Cell

Interdisciplinary scientific initiatives that focus at understanding of the cell are enormous. It started considerably as early as in seventeenth century when an eminent physicist Robert Hooke discovered the cell. The general or microscopic concepts about cells suggest that a collection of varieties of them construct a body. A living system can be subdivided into various functional sections and its smallest unit is cell what contains even smaller structures and hosts a lot of physical natures, trends, and techniques.

Cell Surface Diffusion and Adsorption

Diffusion of adsorbates on cell surface is an important natural process. Once materials reach at the surface of the cell, they fall on a dynamic two-dimensional (2D) plane. The dynamical nature of the constituents of the plane has been explained in detail from a mainly thermodynamic point of view in Chap. 2. The underlying mechanisms of the cell surface diffusion appear with various types of explanations. Biochemical and biological analyses of surface assay experiments provide observation-based explanations on the surface diffusion mechanisms. General physics rules on diffusion and adsorption have been tried to explain the cell surface diffusion and adsorption mechanisms theoretically. Most of the explanations appear with no conclusive and universal models that may explain the general surface diffusion of adsorbates and various other natural materials on and across the quite dynamic plane of the surface of the biological cell. In this chapter, we shall try to address this crucial issue considering some of our self-developed strategies as well as available information from various important studies.

Cell-Based Nanotechnology—Interactions and Energetics

Cells have natural nanometer (nm) scale structures and nanotechnologies active inside. In earlier chapters, we have addressed enough of the nm-dimensional aspects of cells. Cell membrane thickness is of the order of 3–5 nm [for details, see Ashrafuzzaman and Tuszynski (Membrane Biophysics. Springer-Verlag, Berlin Heidelberg, 2012a)], membrane constituent lipid cross section is of the order of 0.6 nm2 (Eze in Biochemical Education 19(4), 1991), membrane-transporting integral ion channels maintain nm dimensions in lengths and cross sections as their dimensions are limited within membrane dimensions, microtubule filaments are of the order of 25 nm diameters, etc.

Cell Surface Dynamics

Cell surface materials are quite dynamic. The timescales of dynamics often fall at the order of millisecond to microsecond or even lower ranges. Both slow and fast dynamics of cell surface are known to follow general physics rules. Cell contains biological components having mostly chemical and physical properties. Cell surface structure can better be explained using its physical properties, specifically mechanical and electrical properties. These properties generally serve the causes of specific surface dynamics. This chapter will focus at an in-depth analysis of the cell surface dynamics.

Quantum Mechanics of the Cell: An Emerging Field

Cell is generally considered a classical system. The molecular structures inside it appear with ultra-level complexities. General physics concepts help construct popular biophysics techniques to understand the energy states and physiological functions of various cellular structures. Besides using statistical mechanics, classical mechanics, and other general physics rules, it is also found recently that quantum mechanics may be utilized to understand some of the crucial cellular aspects.

Molecular Machines of the Cell

Cell is a chemical machine, first proposed by Loeb in 1906. Wilson’s opinion suggested that ‘the specificity of each kind of cell depends essentially on what we call its organization, i.e., upon the construction of the cell machine’ (Wilson in The Cell in Development and Heredity. The Macmillan Company, New York, 1925).

Nanoscale Processes Giving Rise to Ion Pores

Agents such as drugs, peptides, biomolecules that are classified as cell active agents (CAAs) get distributed on the cell surface while they are administered to reach out to cellular targets. Study on cell surface morphology may help us address the distribution of CAAs. Cell surface separates hydrophobic cell membrane core from the cell surrounding water environment. The cell membrane’s outer surface is hydrophilic. In an attempt made by any type of agents to enter into the cell, at the first point of entry, the agents have to get transported naturally or via carriers across the hydrophilic–hydrophobic boundary.