Membrane lipids

A membrane lipid is a compound which belongs to a group of (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipids are amphiphilic: they have one end that is soluble in water ('polar') and an ending that is soluble in fat ('nonpolar'). By forming a double layer with the polar ends pointing outwards and the nonpolar ends pointing inwards membrane lipids can form a 'lipid bilayer' which keeps the watery interior of the cell separate from the watery exterior. The arrangements of lipids and various proteins, acting as receptors and channel pores in the membrane, control the entry and exit of other molecules and ions as part of the cell's metabolism. In order to perform physiological functions, membrane proteins are facilitated to rotate and diffuse laterally in two dimensional expanse of lipid bilayer by the presence of a shell of lipids closely attached to protein surface, called annular lipid shell. A membrane lipid is a compound which belongs to a group of (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipids are amphiphilic: they have one end that is soluble in water ('polar') and an ending that is soluble in fat ('nonpolar'). By forming a double layer with the polar ends pointing outwards and the nonpolar ends pointing inwards membrane lipids can form a 'lipid bilayer' which keeps the watery interior of the cell separate from the watery exterior. The arrangements of lipids and various proteins, acting as receptors and channel pores in the membrane, control the entry and exit of other molecules and ions as part of the cell's metabolism. In order to perform physiological functions, membrane proteins are facilitated to rotate and diffuse laterally in two dimensional expanse of lipid bilayer by the presence of a shell of lipids closely attached to protein surface, called annular lipid shell. The bilayer formed by membrane lipids serves as a containment unit of a living cell. Membrane lipids also form a matrix in which membrane proteins reside. Historically lipids were thought to merely serve a structural role. Functional roles of lipids are in fact many: They serve as regulatory agents in cell growth and adhesion. They participate in the biosynthesis of other biomolecules. They can serve to increase enzymatic activities of enzymes. Non-bilayer forming lipid like monogalactosyl diglyceride (MGDG) predominates the bulk lipids in thylakoid membranes, which when hydrated alone, forms reverse hexagonal cylindrical phase. However, in combination with other lipids and carotenoids/chlorophylls of thylakoid membranes, they too conform together as lipid bilayers. The membrane metabolites of polyunsaturated fatty acids (PUFAs) have an essential role in intercellular biochemical communications. Crawford (2010) in his chapter Long-chain polyunsaturated fatty acids in human brain evolution reported, with regard to the language of lipids, that the importance of the increased complexity of these lipids was brought about by aerobic metabolism, whereby the simple language of prokaryotes, with only a few words, was developed into a vocabulary of over 1,000 words of eukaryote cells. About 500 million years ago, some nervous cells and some gut cells of vertebrates, migrated and specialized in a more complex nervous system: the brain, and in uptake and storage of iodocompounds: the follicular thyroid. In the PUFAs, the presence of a double bond between two carbons (or carbon-carbon double bond) provides them with the possibility of changing their molecular structure through enzymes such as phospholipases, cyclooxygenases and lipoxygenases, etc. The resulting substances, called eicosanoids: prostaglandins (PG), leukotrienes (LT), lipoxins and thromboxane (TX); and docosanoids: resolvins, protectins, and maresins, are powerful lipid mediators that produce specific actions in the organism; they organize inflammation, hemodynamic, immune response and the repair of tissue. Many PUFAs cannot be synthesized by animal organisms and are considered essential, and therefore should be incorporated into diets. These are: linoleic acid (C18:2 n-6), omega-6 and alpha-linolenic (C18:3 n-3) omega-3, arachidonic acid (AA) – omega – 6 (C20: 4n-6), and docosahexaenoic acid (DHA) – omega-3 (C22:6n-3). These PUFAs are incorporated into the phospholipidic membrane of all the cells of an organism. In parallel, ectodermic cells, differentiated into neuronal cells, became the primitive nervous system and brain. Both these cells synthesized iodolipids, as novel words of the chemical lipid language developed among cell membranes during the evolution of life. These biochemical signals among cells, since contact and modification of membranes in multicellular organisms formed the bases of adaptation to terrestrial environments, and their alterations are important in the mechanism of apoptosis, carcinogenesis and degenerative diseases, as well as for understand some problems discussed regarding human evolution (as Aquatic ape hypothesis). Phospholipids and glycolipids consist of two long, nonpolar (hydrophobic) hydrocarbon chains linked to a hydrophilic head group. The heads of phospholipids are phosphorylated and they consist of either: Glycerol dialkyl glycerol tetraether (GDGT) is helping to study ancient environmental factors.