Function Of Phospholipids In The Cell Membrane – If you were to go to the dentist to have a tooth pulled, you wouldn’t want to feel any pain. The dentist would inject an anesthetic into your gum to numb it. One theory for why anesthetics work involves the movement of ions across the cell Membrane. The anesthetic enters the structure of the membrane and causes shifts in the movement of ions across the membrane. If the movement of ions is disrupted, nerve impulses are not transmitted and you feel no pain—at least not until the anesthetic wears off.
A phospholipid is a lipid that contains a phosphate group and is a major component of cell membranes. A phospholipid consists of a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail (see figure below). A phospholipid is essentially a triglyceride in which the fatty acid has been replaced by a phosphate group of some kind.
Function Of Phospholipids In The Cell Membrane
Figure (PageIndex): A phospholipid consists of a head and a tail. The “head” of the molecule contains a phosphate group and is hydrophilic, meaning it dissolves in water. The “tail” of the molecule is made up of two fatty acids that are hydrophobic and do not dissolve in water.
Cell Membrane Structure And Function
According to the “like dissolves like” rule, the hydrophilic head of a phospholipid molecule dissolves easily in water. The long fatty acid chains of phospholipid are non-polar and therefore avoid water due to their insolubility. In water, phospholipids spontaneously form a double layer called a lipid bilayer, in which the hydrophobic ends of the phospholipid molecules are sandwiched between two layers of hydrophilic heads (see figure below). In this way, only the heads of the molecules are exposed to water, while the hydrophobic tails only interact with each other.
Image (PageIndex): In aqueous solution, phospholipids form a bilayer where the hydrophobic tails face each other on the inside and only the hydrophilic heads are exposed to water.
Phospholipid bilayers are critical components of cell membranes. The lipid bilayer acts as a barrier for the passage of molecules and ions into and out of the cell. However, an important Function of the cell membrane is to allow the selective passage of certain substances into and out of cells. This is achieved by embedding various protein molecules into and across the lipid bilayer (see figure below). These proteins form channels through which certain specific ions and molecules can move. Many membrane proteins also contain attached carbohydrates on the outside of the lipid bilayer, which allows it to form hydrogen bonds with water.
Figure (PageIndex): The phospholipid bilayer of the cell membrane contains embedded protein molecules that allow the selective passage of ions and molecules across the membrane. Phospholipids are the major Membrane Lipids that are composed of lipid bilayers. This basic cellular structure acts as a barrier to protect the cell from various external influences and, more importantly, allows numerous cellular processes to take place in the subcellular compartments. Numerous studies have linked the complexity of membrane lipids to signal transduction, organelle functions, as well as physiological processes and human diseases. Recently, the essential roles of membrane lipids in the aging process are beginning to emerge. In this study, we have summarized current advances in our understanding of the relationship between membrane lipids and aging, with an emphasis on phospholipid species. We investigated how the major species of phospholipids change with age in different organisms and tissues, and some common patterns of membrane lipid change during aging were proposed. Furthermore, the functions of various phospholipid molecules in regulating health and lifespan were discussed, as well as their potential mechanisms of action.
Captivating Facts About Phospholipids
The relationship between lipids and aging was well known. Fatty acid (FA) content, composition, and metabolism are altered in old or long-lived humans and model organisms (Papsdorf and Brunet, 2019). In addition, studies in model organisms such as Caenorhabditis elegans revealed that various types of FA could extend lifespan when supplemented in a diet that includes monounsaturated oleic acid, palmitoleic acid, cis-vaccenic acid, and oleoylethanolamine, as well as polyunsaturated acid and – linoleum. , arachidonic acid and dihomo-g-linolenic acid (Goudeau et al., 2011; Rourke et al., 2013; Folick et al., 2015; Han et al., 2017; Qi et al., 2017). These unsaturated FAs mainly function through classical longevity factors such as DAF-16/FOXO3, SKN-1/Nrf2, and HSF-1/HSF1 to regulate health and lifespan (Labbadia et al., 2015; Steinbaugh et al., 2015 Papsdorf and Brunet, 2019).
Despite these advances linking FAs to longevity regulation, little is known about their mechanisms of action. In general, FAs function through several major mechanisms, including signaling molecules, energy sources, substrates for post-translational modifications, and components of complex lipids (Van Meer et al., 2008; Shimizu, 2009; Nakamura et al., 2014; Saliba et al., 2015; Resh, 2016; Harayama and Riezman, 2018). Consider, for example, oleoylethanolamine, which acts as a signaling molecule and regulates animal lifespan by directly binding and activating the nuclear hormone receptor NHR-80 (Folick et al., 2015). To date, however, only a few FAs have been found that exert their functions directly as signaling molecules or as substrates for post-translational modifications. Most MKs are incorporated into complex lipids, such as membrane lipids, as their acyl chains, thus influencing membrane structure, composition, and function (Van Meer et al., 2008; Sezgin et al., 2017; Harayama and Riezman, 2018). Therefore, it is conceivable that FAs may regulate lifespan by acting as important components of membrane lipids, potentially linking membrane homeostasis to lifespan regulation.
Membrane lipids, mainly phospholipids (PL; also known as glycerophospholipids), consist of a lipid bilayer that acts as a barrier between the cell and the environment and between different cellular compartments. However, numerous studies indicate that the lipid bilayer functions not only as structural barriers, but also plays an essential role in the regulation of many cellular processes (Shimizu, 2009; Wu et al., 2016; Sunshine and Iruela-Arispe, 2017; Harayama and Riezman, 2018) . This idea is also supported by the diversity of membrane lipids (different kinds of membrane lipids and different acyl chains within certain membrane lipids) (Hishikawa et al., 2014; Antonny et al., 2015), which is much more than the need for barrier function. Regarding the aging process, studies in several model organisms have reported an association of the content and composition of many membrane lipids with animal age (Papsdorf and Brunet, 2019), supporting the potential role of membrane lipids in modulating aging. In this review, we focused on PL and summarized recent advances that link PL homeostasis to the aging process and discussed their potential mechanisms of action. Other membrane lipids, such as sphingolipids, were not discussed in this review.
Phospholipids are the major structural lipids of the eukaryotic membrane, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA), and cardiolipin (CL). These major PL species share similar structures containing two FAs attached to the sn-1 and sn-2 positions and a different phosphate head group at the sn-3 position of the glycerol backbone. The different compositions of these PLs may account for the membrane diversity of the various subcellular compartments and thus for the functions of the organelles. Take PCs as an example, they are the most abundant PLs, accounting for more than 50% of the total PLs in the cell. It is mainly located in the endoplasmic reticulum (ER), the site of membrane lipid biosynthesis, but its content is relatively less in the plasma membrane (Van Meer et al., 2008). Maintenance of PC homeostasis is critical for organellar function, while reduction of PC represents a cellular stress known as lipid bilayer stress (Volmer et al., 2013; Halbleib et al., 2017; Shyu et al., 2019). The cell therefore develops an elegant adaptive mechanism to survey PC content, and PC loss has been found to affect multiple cellular processes through this stress-responsive pathway (Koh et al., 2018; Ho et al., 2020). Another extreme example of diversity in PL composition is organelle-specific PLs. CL is a mitochondrial-specific membrane lipid whose content has been found to have a major impact on mitochondrial function and to be associated with various mitochondrial diseases (Chicco and Sparagna, 2007; Houtkooper and Vaz, 2008; Schlame, 2008; Pizzuto and Pelegrin, 2020).
Probing The Role Of Chirality In Phospholipid Membranes
The composition of the acyl chain also accounts for the diversity of PLs, which vary greatly in chain lengths and the numbers and positions of double bonds. These chemical variations can affect membrane protein-lipid interactions and thus the cell signaling properties of membrane proteins (Antonny et al., 2015; Saliba et al., 2015; Wu et al., 2016; Harayama and Riezman, 2018). Additionally, PLs containing unsaturated acyl chains are more fluid than saturated ones, and thus the overall degree of FA unsaturation in PLs could affect membrane fluidity, which has been found to regulate numerous signaling pathways, cellular processes, and human diseases (Los and Murata, 2004; D ‘Auria and Bongarzone, 2016; Ammendolia et al., 2021). Therefore, when it comes to the study of aging, it is important to understand how PL content and composition interacts with proteins in longevity pathways and how such interactions determine health span and lifespan. In the following section, we discuss the relationship between aging and basic PLs.
Several studies have been reported
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