Composition of biological membranes

V. M. Mazhul, Y. S. Ermolaev, and C. V. Konev, Tryptophan phosphorescence at room temperature New method for the study of the structural composition of biological membranes and proteins in cells, Zh. Prikl. Spectrosk. 32, 903-907 (1980). 

It is therefore not surprising that in many cases a suitable preparation of liposomes is a better model for describing drug distribution into specific tissues than log Poct. To select the best liposome preparation remains, however, a problem until we know more about the individual composition of biological membranes in different tissues and their possible interaction modes with certain drug structures. 

IMS allows the visualization of these multiple molecular species in parallel. The distinct localization of GPL molecular species can be determined in other words, the distinct fatty acid composition of biological membranes in different tissue locations can be determined. 

This chapter discusses the composition, structure, and dynamic processes of biological membranes. 

Native biological membranes also display characteristic phase transitions, but these are broad and strongly dependent on the lipid and protein composition of the membrane. 

It is necessary to elaborate on yet another essential aspect of biological membranes, i.e. their complexity . This keyword points to the large number of different molecules that are usually found in the biological membrane. First of all, there is a large variety of lipid molecules. The lipid composition of the biological membranes varies from one species to another, and is adapted to meet the needs of organs, cells, organelles, etc. The variations in the head-tail... 

An important approach to the study of biological membranes has been the preparation and study of model membranes. According to current usage, model membranes include lipid bilayers and lipid bilayers into which have been incorporated additional components such as one or more membrane proteins. It is through the study of such model membranes that one has the best opportunity to isolate and study fundamental physical chemical and biophysical processes, and it is for this reason that the present report emphasizes these systems. A discussion of model membranes necessarily starts with a description of the chemical compositions and physical properties of lipid molecules. 

In this chapter we first describe the composition of cellular membranes and their chemical architecture— the molecular structures that underlie their biological functions. Next, we consider the remarkable dynamic features of membranes, in which lipids and proteins move relative to each other. Cell adhesion, endocytosis, and the membrane fusion accompanying neurotransmitter secretion illustrate the dynamic role of membrane proteins. We then turn to the protein-mediated passage of solutes across membranes via transporters and ion channels. In later chapters we discuss the role of membranes in signal transduction (Chapters 12 and 23), energy transduction (Chapter 19), lipid synthesis (Chapter 21), and protein synthesis (Chapter 27). 

One approach to understanding membrane function is to study membrane composition—to determine, for example, which components are common to all membranes and which are unique to membranes with specific functions. So before describing membrane structure and function we consider the molecular components of membranes proteins and polar lipids, which account for almost all the mass of biological membranes, and carbohydrates, present as part of glycoproteins and glycolipids. 

A casual examination of the general chemical composition of membranes from mammalian cells reveals that over 90% of their (dry weight) mass is comprised of proteins and phospholipids (in the main). The weight ratio of these two major classes of compounds may vary considerably from one source to another, ranging from 3 1 in myelin to 1 3 in mitochondria. While no definitive figure can be cited for the minimal amount of phospholipid and/or protein required for a membrane structure, it is abundantly clear that any ultimate disclosure of the architecture and behavior of biological membranes... 

This fatty acid composition results in a more rigidly parallel structure, which has led to the assumption that these lipids are only structural components of biological membranes and not metabolically active (or activatable) compounds. This assumption may have to be revised pending continuing studies on the role of sphingosine-like compounds in signal transduction. 

Be familiar with the composition and structure of biologic membranes. Be able to place the various phospholipids in the membrane bilayer. Know the function and position of membrane proteins and their possible movements. Know how membrane fluidity is controlled. Know the nature of various mechanisms to transport substances across membranes, receptor-mediated endocytosis, active and facilitated transport, ionophores, and the various types of channels. Be able to solve simple mathematical problems by creating solute gradients across membranes. Know the names of substances that inhibit the various modes of transport across membranes. 

Edwards-Webb, J.D.,Gurr, M.I. 1988. The influence of dietary fats on the chemical composition and physical properties of biological membranes. Nutr. Res. 8, 1297-1305. 

DSC has been used to study the individual protein components of biological membranes of relatively simply protein composition and the interaction of several of these components with lipids and with other proteins. The red blood cell membrane, which has been most intensively studied, exhibits five discrete protein transitions, each of which has been assigned to a specific membrane protein. The response of each of these thermal transitions to variations in temperature and pH as well as to treatment with proteases, phospholipases, specific labelling reagents, and modifiers and inhibitors of selected membrane activities, has provided much useful information on the interactions and functions of these components in the intact erythrocyte membrane (46-49). Similar approaches have been applied to the bovine rod outer segment membrane (50) and to the spinach chloroplast thylakoid membrane (51). 

Rilfors L, Lindblom G. Regulation of lipid composition in biological membranes - biophysical studies of lipids and lipid synthe- 60. sizing enzymes. Colloids Surf. B 2002 26 112-124. 

To begin with, biological membranes are not uniform with respect to membrane sidedness. Both the protein and the lipid composition of these membranes exhibit transbilayer asymmetry. In addition, in polarized mammalian cells, a segregation... 

The most prominent function of biologic membranes is to control selectively the molecular transport into and ont of cells. The ability of certain molecnles to traverse such biologic barriers depends on their composition as well as their strnctnral and functional features. These features are discussed in more detail on a molecular level elsewhere in this encyclopedia. In... 

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