U an familiar Thank you . The question I have what keeps the Phospholipids from disintegrating , I believe thew general assumption is that the membrane is like a micelles, but you can disintegrate a micelles by diluting and cells you don't disintegrate by diluting , So I think there must be some interphospholipid bonding ?
One side (phosphate) is hydrophilic (likes water) other side (lipid) is hydrophobic. Therefore they are aranged in a bilayer with the phosphates out and the lipids touching lipids.
I can't definitively answer your question; I'm not much of a biochemist. But I can say that whilst a phospholipid micelle is a useful conceptual analogy, a plasma membrane is a lot more complex than a simple phospholipid micelle. If you take into consideration the following, perhaps you can appreciate that the PM will not behave like a simple micelle. Taking animal cells as an example, there are five major phospholipids that comprise the PM – phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, sphingomyelin and phosphatidylinositol. Distribution of the different lipids varies between the outer and inner leaflet. In addition to the phospholipids, the PM contains glycolipids and cholesterol. Glycolipids are a minor component whereas cholesterol is a major membrane constituent of animal cells, being present in about the same molar amounts as the phospholipids. Of course, there are many proteins in a PM, the so-called ‘peripheral’ and ‘integral’ membrane proteins. Lipids are the fundamental structural elements whereas proteins are responsible for carrying out specific membrane functions. Most plasma membranes consist of approximately 50% lipid and 50% protein by weight, with the carbohydrate portions of glycolipids and glycoproteins constituting 5 to 10% of the membrane mass. Many of the peripheral membrane proteins are components of the cortical cytoskeleton, which underlies the plasma membrane and determines cell shape and contributes to cell function, eg. spectrin, actin, ankyrin. Ankyrin serves as the principal link between the plasma membrane and the cytoskeleton. There are a number of linkages between cytoskeleton and PM. In contrast to transmembrane proteins, a variety of proteins (many of which behave as integral membrane proteins) are anchored in the plasma membrane by covalently attached lipids or glycolipids, eg. glycosylphosphatidylinositol (GPI) anchors. GPI anchors are added to certain proteins that have been transferred into the endoplasmic reticulum and are anchored in the membrane by a C-terminal transmembrane region. Other proteins are anchored in the inner leaflet of the plasma membrane by covalently attached lipids. Rather than being processed through the secretory pathway, these proteins are synthesized on free cytosolic ribosomes and then modified by the addition of lipids. Info taken from various sections of: The Cell: A Molecular Approach (2nd ed) Cooper GM. Sunderland (MA): Sinauer Associates; 2000.
Thank you for the multiple points. I know my comparison to micelles is to simple , there have to be some covalent or ionic bonding in order to give the membrane strength , as you pointed the attached molecules like inositol, ethanol amine and others, but thanks again.
A very important membrane consideration is the importance of phosphate. If the phospholipids did not have phosphate, water and lipids would form two phases like an oil and water mixture. If we add phosphates to the lipids, the little bead of oil changes to a bi-layer shell. Phosphate is also an important part of materials like DNA and RNA, as well as energy rich molecules like ATP. If we took the phosphate away from these materials their properties would be much different. Without phosphate, even the DNA will not work because it would be all balled up by aqueous surface tension and be hard to use as a template. What I found interesting is why the external boundary and the generic materials are so dependent on the same phosphate induction?
