What is the function of phospholipids

Phospholipids, also called phosphatides, are found in every cell in the human body and belong to the family of membrane lipids. You make that Main component of the lipid bilayer of a biomembrane, for example the cell membrane. In the myelin membrane of the Schwann cells, which surround the axons of the nerve cells, the phospholipid content is particularly high. It is around 80% [5]. Are phospholipids amphipolar lipids, that is, they are composed of a hydrophilic head and two hydrophobic hydrocarbon tails [1, 5]. Phosphatides consist of fatty acids and phosphoric acids, on the one hand with the alcohols glycerine or sphingosine, on the other hand with the nitrogen-containing active groups Choline, Ethanolamine, Serine or inositol are esterified [1, 5]. The phosphoglycerides or glycerophospholipids, which have the trivalent alcohol glycerine as a building block, are the most common in nature [5].

The most common phospholipids found in a cell membrane include:  

  • Phosphatidyl choline - lecithin, PC
  • Phosphatidyl serine (PS)
  • Phosphatidylethanolamine (PE)
  • Sphingomyeline (SM)

Phosphatidyl serine is exclusively in the inner layer of the cell membrane - cytoplasmic side -, Sphingomyelin for the most part in the outer layer of the biomembrane - exoplasmic side - to be found [1].
Phosphatidyl choline and Phosphatidylethanolamine are enriched in both membrane layers, but in different concentrations. PC is predominantly part of the exoplasmic side, while PE mainly belongs to the cytoplasmic side of the cell membrane [1]. The need for phospholipids is produced by the body itself or ingested through food and supplied to the body cells after its own synthesis [3]. The phosphatide content of an organ of the organism - including the plant - is distributed differently. High phospholipid concentrations are mainly found in bone marrow (6.3 to 10.8%), brain (3.7 to 6.0%), liver (1.0 to 4.9%) and heart (1.2 to 3, 4%) [2, 3].

Functions

Phospholipids have different properties. This is due on the one hand to their oppositely charged head groups - phospholipids in the outer membrane are positive, those in the inner membrane are negatively charged or neutral - and on the other hand to the fatty acids [1, 5].

The amount and relative composition of the fatty acids in the phospholipids, which depends on the food intake, is very important. For example, a high proportion of polyunsaturated fatty acids, such as arachidonic acid (AA) and eicosapentaenoic acid (EPA), of importance, since AA and EPA are important lipid mediators Prostaglandins PG2, PG3 generated from phospholipases [1, 5]. Prostaglandins influence blood pressure, blood clotting, lipoprotein metabolism and allergic and inflammatory processes, among other things [3, 4, 6]. Phospholipids impart certain general properties to cell membranes.

The phospholipids, together with other membrane components, such as cholesterol, proteins and carbohydrates in the form of glycolipids and glycoproteins, are in constant motion, which means that the biomembrane is in a "liquid-crystalline" state [5]. This varies with more or less intensive movement of the membrane components Degree of fluidity (Flowability). Among other things, the lipid composition of the membrane is decisive for this [5]. The more unsaturated fatty acids in the membrane, the more permeable it is for water. Thus, the fluidity elevated [1]. This effect is based on the cis double bonds of the unsaturated fatty acids, which cause a “kinking” of the fatty acid tails and thus a disruption of the ordered “crystal structure” of the membrane [5]. The phospholipid bilayer of the plasma membrane has a barrier function [1, 5]. This barrier is essential so that the cell's constituents cannot mix in an untargeted manner with the extracellular medium. The existence of the plasma membrane is therefore important in order to prevent a breakdown of the cellular metabolism and thus cell death [1, 5].

literature

  1. Berg JM, Tymoczko JL, Stryer L: Biochemistry. Spectrum Academic Publishing House; 2003; 5th edition
  2. Elmadfa I, Leitzmann C: Human nutrition. 134-138. Publishing house Eugen Ulmer Stuttgart; 2004; 4th, corrected and updated edition
  3. Tap A: Dietary Supplements. 206-210, 214-218. Wissenschaftliche Verlagsgesellschaft mbH Stuttgart 2001
  4. Kasper H: Nutritional Medicine and Dietetics. 11-23. Urban & Fischer Verlag; Elsevier GmbH, Munich 2004
  5. Rehner G, Daniel H: Biochemistry of Nutrition. 7-14. Spectrum Academic Publishing House Heidelberg / Berlin; 2002; 2nd revised and expanded edition
  6. Schmidt E, Schmidt N: Guide to micronutrients. 337-342. Urban & Fischer Verlag; Munich, February 2004

     
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