Lipids in cellular structures

Before describing the composition, structure and function of membranes, it is necessary to detail the molecules which make up the lipid components. 

1 Phosphoglycerides are the major lipid components of most biological membranes 

The stereochemistry of phosphoglycerides was discussed in Chapter 1. The phosphoglycerides are a very widespread and diverse group of structures. In most membranes they are the main lipid components and, indeed, the only general exceptions to this statement are the photosynthetic membranes of plants, algae and cyanobacteria and the archaebacterial membranes. 

The simplest phosphoglyceride contains only phosphoric acid attached to diacylglycerol and is called phosphatidic acid (Table 6.3). Where additional X groups are esterified to the phosphate moiety the lipids are called phosphatidyl-X. Major types of such diacylphosphoglycerides are shown in Table 6.3 where relevant comments about their distribution and properties are made also. 

Animals. First isolated from egg yolks. Higher plants. Rare in microorganisms 

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Gurr, M.I. Harwood, J.L. Lipids in cellular structure membrane structure. In Lipid Biochemistry Chapman and Hall London, 1991 265-281. 

Our data on both disappearance of a reactant (O2 consumption) and the formation of a product (lipid-derived radical) clearly support the conclusion that cellular oxidizability increases exponentially with MBI. This exponential relationship of cellular oxidizability and polyunsaturation could be due to the close packing of unsaturated lipids in the structured environment of the membrane. 

While there is no doubt that free lipids can facilitate the formation of hemozoin in model systems, their potential biological role must be placed in the appropriate context. The vast majority of these lipids are involved in cellular structures (organism membrane, organelles, etc.), not freely soluble in the cytoplasm. The methods of extraction modified from Bligh and Dyer [35] by Cohen [36] were designed to extract all of the available... 

The metabolic role of lipids and the manner in which they operate in cellular structures is increasingly better understood. This understanding has allowed for the developments of a diverse number of applications both in the pharmaceutical and cosmetic fields. The major types of lipids that are present in the human body and/or play major roles in metabolic processes are triacylglycerols (TAGs), free... 

The other phases are less exotic. The mesh phases consists of lamellae with ordered holes, while ribbon phases are deformed cylinders on a rectangular lattice (see Fig. 12-22). These phases can are usually type I phases with the tails inside the deformed cylinders or inside the hole-filled lamellae, but they could also be inverse, type II, phases. Type II mesh and ribbon phases seem not to have been reported much type II strut phases are common for two-tailed lipids, such as those in cell membranes. In fact, type II strut phases evidently serve biological functions, since they have been found to exist in cellular structures such as the endoplasmic reticulum and the mitochondrion (Seddon 1996). 

Schmitz G, Liebisch G, Langmann T (2006) Lipidomic strategies to study structural and functional defects of ABC-transpoiters in cellular lipid tr afficking. FEBS Lett 9 5 80(23) 5597-610. Review... 

Fig. 10.9 Possible reaction pathway for the formation of a cell. The important precursors are an RNA replicase and a self-replicating vesicle. The combination of these two in a protocell leads to a rapid, evolutionary optimisation of the replicase. The cellular structure is completed if an RNA-coded molecular species, for example, a lipid-synthesised ribozyme, is added to the system (Szostak et al., 2001)... 

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