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Molecular Biology of Thermophilic and Psychrophilic Archaea
Published in Ajar Nath Yadav, Ali Asghar Rastegari, Neelam Yadav, Microbiomes of Extreme Environments, 2021
Chaitali Ghosh, Jitendra Singh Rathore
Biological membranes are typically a bilayer structure of phospholipids which interact with each other via non-covalent bonds including Van der Waals bond as well as electrostatic interactions. To ensure proper lipid mobility and maintain constant fluidity, by adapting the lipid composition in response to physical environments such as temperature and pressure are the most important properties of membrane. Lipid bilayers have a complicated melting behaviour of undergoing a transition from a crystal or gel phase to a liquid state. At the optimum growth temperature, membranes are present in a liquid crystalline state. Such a state has a high degree of lipid movement which govern proper functioning of membrane proteins as well as maintenance of the barrier function (Melchior 1982). Membrane fluidity is dependent on the chemical structure of its lipids and by changing the lipid composition in response to environmental factors; the organisms can control membrane fluidity.
The Cell Membrane in the Steady State
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
In living cells, the basic phospholipid bilayer structure is modified in several respects so as to serve the many important functions required of the cell membrane. Cell membranes have an abundance of cholesterol and protein molecules (Figure 2.2). Cholesterol is a small steroid-type molecule having a hydrophilic OH group, that aligns with the polar heads of the phospholipid molecules, and a hydrophobic portion that nestles between the fatty acid chains. On the one hand, cholesterol makes the membrane more fluid and flexible by preventing the fatty acid chains from forming a more rigid, crystal-like structure. On the other hand, the attraction to the fatty acid chains makes the membrane firmer and less permeable to small, water-soluble molecules. In addition, cholesterol plays a significant role in mechanically securing protein molecules in the membrane so that they are not adversely affected by membrane fluidity.
Monolayers and Multilayers
Published in Victor M. Starov, Nanoscience, 2010
Hernán Ritacco, Iván López-Montero, Francisco Monroy, Francisco Ortega, Ramón G. Rubio
All of these properties of the membrane lipids are not accidental but carefully designed by nature to ensure three essential properties of biomembranes. Membrane self-assembling: the biological lipids spontaneously self-assemble into bilayers that can compartmentalize different regions within a cell as well as separate the inside from the outside.Membrane robustness: because of their extremely low critical aggregation concentration, the membranes remain intact even when lipids were strongly depleted from the medium.Membrane fluidity: unsaturation, chain branching, and cholesterol-driven fluidity regulation ensure the membrane in the fluid state at physiological temperatures, hence allowing for nonimpeded transport of lipids and proteins inside.
Fatty acids and survival of bacteria in Hammam Pharaon springs, Egypt
Published in Egyptian Journal of Basic and Applied Sciences, 2018
Yehia A. Osman, Mahmud Mokhtar Gbr, Ahmed Abdelrazak, Amr M. Mowafy
Exhaustive literature survey led us to admit that every living creature (species) establishes its own niche with its own living habitat. In which, a relationship is specifically invented between an organism and its living surrounding conditions including not only the different members of all populations living within the same niche but also temperature, pH and nutrients. Hence, adaptability of the cellular component of native species is expected for survival under these conditions. Accordingly, cell structure and specially the cell membrane lipids are the determinants of the survival and flourish of the organisms. Temperature selectively affects the type of lipids, unsaturation status and the degree of membrane fluidity. This vital role played by temperature also dictates that cells cannot grow at temperatures lower than that of their lipids solidification point [21,22] . This is consistent with the first order proposal of Brock and Ingraham [23,31] about the thermal death of the organism. The peculiarity of fatty acid unsaturation, chain length, branching and cyclization all contribute significantly to the adaptability of the thermophiles to their environments. However, the type of fatty acids did change between moderate and extreme Thermophilic bacteria, except no hydroxy, cyclopropane, or unsaturated fatty acids were found [20].
Effects of certain physical stresses on the composition of the membrane of bacteria implicated in food and environmental contamination
Published in International Journal of Environmental Health Research, 2022
SalmaKloula Ben Ghorbal, Rim Werhani, Chatti Abdelwaheb
It is evident that bacteria are able to cope with environmental stress conditions. However, they aren’t able to transport away from environmental disturbance and this leaves their membranes at once faced to outside environment and open to physical and chemical perturbations (Denich et al. 2003; Gamalero et al. 2020; Qi et al. 2019). Bacterial membranes, which consist principally of lipids, are involved in the adjustment process of Gram-positive and Gram-negative bacteria to numerous environmental stresses (Mbye et al. 2020). The Gram-negative outer membrane has been shown to act as a permeability barrier, but recent studies have uncovered a more extensive and versatile role for the outer membrane in protecting cells from threatening conditions (Sun et al. 2022). Lipids are molecules that may adjust in reaction to numerous environmental disturbances. Changing membrane integrity and permeability, which can be essential for bacterial protection, is frequent because of a shift in lipid composition by converting the ratio of saturated–unsaturated fatty acids (FA) (Tatzer et al. 2002) . The modification of membrane fluidity is mediated by changes in the level of unsaturated fatty acids (UFA), by action of FA desaturases. Therefore, the adjustment of membrane fluidity maintains an environment suitable for the function of certain critical integral proteins during stress (Miller et al. 2010). Moreover, a rapid isomerization of cis into trans unsaturated fatty ends in a brief rigidification of the cell membrane, a mechanism recognized in a few Gram-negative micro organisms (Eberlein et al. 2018). Modifications within side cell membrane might additionally have an effect on the membrane fluidity as a way to keep membrane integrity face to harsh condition. Therefore, environmental elements together notably, UV radiations, magnetic and static fields (Kloula Ben Ghorbal et al. 2013, 2021), can alter the organization and composition of the membrane, without forgetting all elements, especially age of growth, which can interfere in membrane compositional modifications, after exposure to at least one or numerous stressor elements (Denich et al. 2003).
Hyperlipidemia and male infertility
Published in Egyptian Journal of Basic and Applied Sciences, 2021
Zainab Bubakr Hamad Zubi, Hamad Abdulsalam Hamad Alfarisi
Mammalian sperm cell membrane has a lipid bilayer consists of phospholipids and cholesterol. During passage of sperm from the testes to the female genital tract, sperm membrane undergoes several modifications. Membrane lipids particularly cholesterol are responsible for the physiological alterations in the membrane fluidity and cell responsiveness to the environment [40]. Cholesterol of sperm plasma membrane regulates membrane permeability, lateral mobility of integral proteins and functional receptors within the membrane. Loss of cholesterol from the membrane is responsible for destabilization of the membrane during capacitation [44]. Capacitation is the functional maturation of the sperm which takes place within the female genital tract. It is essential for the sperm ability to fertilize an egg. It involves changes in the sperm head and flagellum including the ability of sperm to undergo acrosomal reaction and acquisition of motility hyperactivation [45]. The initial step toward the capacitation is the removal of sperm external coating-proteins that protect the sperm on its path to oocyte and prevent early occurrence of acrosomal reaction [44]. Cholesterol efflux from the sperm membrane causes a decrease in the cholesterol/phospholipid ratio which leads to changes in the membrane fluidity and causes membrane protein redistribution that required for capacitation [46]. It is also important for signaling mechanisms that regulate capacitation process. Signaling mechanisms can be initiated through the cholesterol loss via two mechanisms: 1) an interaction between membrane proteins which occurs as a subsequent to the increase in the membrane fluidity and 2) freeing of certain signaling molecules from their interaction with cavolin giving them the ability to form specific signaling complexes [47]. Cholesterol efflux is an early event in the capacitation followed by a reduction in the cholesterol/phospholipid ratio which changes the membrane dynamics and increases its permeability to bicarbonate and calcium ions. This is followed by the activation of adenylyl cyclase and increase production of cyclic adenosine monophosphate (cAMP). A signal cascade initiated through activation of protein kinase A (PKA) which phosphorylates sperm protein tyrosine residue. Finally, the sperm acquire hyperactive motility and the ability to bind to zona pellucida to undergo the acrosomal reaction [48]. Hypercholesterolemia alters the concentration and distribution of cholesterol of sperm plasma membrane and subsequently reduces the acrosomal reaction and capacitation [40,41]. High cholesterol level inhibits capacitation either through its direct effect on certain surface proteins that have roles in signaling transduction, or indirectly via restricting the conformational changes of sperm surface proteins and consequently decreases their activity [47].