The Scientific Research Notes of S. Sunkavally. Years: 1986 - 1990.
Page 145.
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The Scientific Research Notes of S. Sunkavally. Years: 1986 - 1990.
Page 145.
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The Scientific Research Notes of S. Sunkavally, Printed Part, page.111.
Dates unclear, but certainly between 2006-2012.
Cell membranes: the awesomeness inside you.
Read the full paper at: http://www.scirp.org/journal/PaperInformation.aspx?PaperID=49955 DOI: 10.4236/ojbiphy.2014.44012 Author(s) Michaela Sieber, Wolfgang Hanke, Florian P. M. Kohn ABSTRACT Biological membranes are preferentially composed of lipids and proteins, and it is assumed that mainly the proteins are responsible for their functional properties. Nevertheless, during the last years, the contribution of the plain lipid matrix and its physico-chemical parameters to membrane functionality has been shown to be of high relevance. This is also correct for the gravity dependence of cells and organisms which is well accepted since long for a wide range of biological systems. Thus, the question must be asked, whether, and how far plain lipid membranes are affected by gravity directly. In this study we show that the fluidity (viscosity) of plain lipid membranes, as well as that of cell membranes, is gravity dependent, using a multipurpose 96-well plate reader in the fluorescence polarization anisotropy mode in a parabolic flight mission. EWW140925GJR Plain lipid vesicles and cells from a human cancer cell line have been used in these experiments. Necessarily, membrane-integrated proteins should be affected by this in their function. As a consequence any living cell will be able to sense at least basically gravity. KEYWORDS Microgravity, Cells, Liposomes, Membrane Fluidity, Fluorescence Polarisation Anisotropy
Membrane Structure: Fluidity
In order for a whole host of cellular processes to work, the membrane must be fluid. This basically means that phospholipids can’t be static and rigid; they must have spaces between them and must be allowed to move around, more like a fluid than a solid. Think of the lipids as like corks on the water, allowed to move up and down, side to side, rotate around, and flip head to tail. The fluidity of a membrane determines how molecules are transported and how signals are sent, which are both vital to cell function.
There are several different physical factors that affect membrane fluidity:
Temperature—when the membrane is heated, lipids will gain energy and so they’ll move around more. At low temperatures, lipids don’t have this energy to move and so they’ll just stay in their organised configuration. All membranes have a “melting point”, where they change from their solid/gel phase to their liquid phase, and this point is determined by their lipid composition.
The degree of saturation of the fatty acids—i.e., how tightly the lipids are packed together. This is determined by how the carbons in the phospholipid tails are bonded. Double bonds between two carbons create kinks in the tails that make space between the lipids. The membrane is therefore less densely packed, meaning it’s more fluid. Single bonds, on the other hand, decrease fluidity because they’re stiff and straight.
Cholesterol. Cholesterol exists between the fatty acid tails of phospholipids, which stops the intermolecular forces between the lipids from being so strong. This allows the membrane to remain fluid even at low temperatures, so sterols act as a sort of regulator. They can also act as stabilisers, filling in gaps caused by the kinks.
Membrane proteins. Protein-lipid interactions and protein-protein interactions can sometimes prevent or promote movement, and having a lot of proteins can impose restrictions on membrane mobility
Interesting fact: hibernating animals can change their lipid composition in order to maintain membrane fluidity throughout the winter.
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Biochemistry and Physiology of Substance Abuse
The purpose of this series is to provide a resource for concise, detailed reviews of key aspects of the biochemistry of substances of abuse. This text presents pertinent research findings on various effects of drug and alcohol abuse by knowledgeable specialists in this field. Some biochemical changes considered include immunomodulation, altered disease resistance, membrane fluidity and functional modifications, teratogenic effects, and modifications of hormonal regulation and production with major functional consequences. Chapters summarize and evaluate in detail the advances made in understanding the changes in biochemistry or physiology caused by various drugs of abuse. Various drugs of abuse, particularly alcohol and major elicit compounds are emphasized. Information on their effects on nutrition, immunology, biochemistry, metabolism, and pharmacology are included. This text will assist the researcher, Biochemistry and Physiology of Substance Abuse clinician and student in comprehending the complex changes caused by the direct and indirect effects of single drugs at the cellular level.