Peptide Self-Regulation of Living Systems (Facts and Hypotheses) - Shataeva L. K. 2003

Peptide Interactions with the Cell Membrane

It can be considered that the elementary biological unit capable of independent existence in the absence of other living organisms is The Cell. It is separated from the external environment by a cytoplasmic (plasma) membrane, which ensures the constancy of the cell's internal composition regardless of environmental changes. In other words, it provides many (though not all) of the cell's self-regulation mechanisms. As is known, Introduction/36.html">Biological Membranes consist of Phospholipids, which form a lipid bilayer, and Proteins embedded within this bilayer, sometimes referred to as integral proteins. The mechanical strength of such membranes is low and cannot protect the cell from external mechanical damage. In simple microorganisms (Bacteria), an external Cell wall plays an additional protective role, with peptidoglycans as its main components. The Cells of higher organisms lack a rigid cell wall, but their Plasma Membrane is surrounded by an outer envelope (the so-called Extracellular matrix, or glycocalyx), which consists primarily of acidic Polysaccharides and Glycoproteins.

The interior space of a living cell contains an extensive network of Endoplasmic reticulum membranes. In addition, the Organelles present in the Cytoplasm are also surrounded by their own membranes (Nucleus, Mitochondria, Liposomes, Peroxisomes). From the perspective of modern membrane technology, The Eukaryotic Cell is a multi-compartment and multifunctional membrane system. Under this approach, all body fluid can be divided into extracellular and intracellular. Extracellular fluid includes interstitial fluid, Lymph, and Blood Plasma, which amounts to approximately 15.5 L in a 70 kg human body. The volume of intracellular fluid reaches 26.5 L (Oxford Dictionary..., 1997). These volumes are separated by plasma cell membranes, the total area of which reaches many hundreds of square meters. Intracellular fluid contains higher concentrations of potassium, magnesium, sulfates, and phosphates, and lower concentrations of bicarbonates and sodium chloride compared to extracellular fluid. It is the Plasma Membranes that carry out intensive selective two-way transport of these salts, Water, and metabolites, although the characteristics of transmembrane fluxes are highly specific for each type of tissue.

Class="center">Table 9 Biological membranes of various classes (after: Kagawa, 1985)

Y. Kagawa (1985) proposed a Classification of biological membranes in higher organisms. With some Abbreviations, this classification is presented in Table 9.

The mobility of the plasma and intracellular membranes is provided by the Cytoskeleton—the cell's supporting Structure, which consists of non-membranous (lamellar) structures: microtubules and filaments.

In the region of the cell surface of a multicellular organ where interaction with the external environment occurs (for example, epithelial Cells of the Small Intestine with the intestinal contents), numerous microvilli are located, increasing the actual surface area for the active and passive transport of metabolites (Kagawa, 1985). In the area of intercellular contacts, Electron Microscopy has revealed Three types of structures: tight junctions, Gap Junctions, and connexon-mediated contacts.

In the zone of a tight junction, two plasma membranes come into complete contact, yet the cytoplasmic spaces of the two contacting cells remain isolated from each other. These tight Intercellular junctions are most developed in the Skin epithelium and Brain capillary endothelium, serving as effective barriers to water and hydrophilic components. Hereafter, we will restrict our Discussion specifically to Cytoplasmic membranes.