What is the role of phospholipids in the transfer of molcules across the cell membrane?

Answer 1

Phospholipids play a couple of important roles at the cell membrane. First and foremost, the "lipid bilayer" that actually IS the cell membrane is formed of predominantly phospholipids. The structure of the molecule is termed "amphipathic" which means that it has at one end the property of interacting with water (this is the phosphate group, which has a charge and therefore hydrogen bonds with water nicely), and at the other end, the long chain fatty acid hydrocarbon tails are hydrophobic/lipophilic. The membrane is made of 2 layers of organized phospholipids which are oriented so that the phosphate groups face outward and form both of the membrane's surfaces.

Because of this structured orientation, ionic molecules cannot worm through the membrane. Instead, they are only able to cross where specialized intramembrane protein structures termed "channels" exist. These channel proteins are involved with the control of what goes in and what leaves the cell.

Lipid molecules, on the other hand, have a much easier time crossing the membrane passively. However, since lipid molecules do not freely float around in the water based environment that surrounds cells, cell-to-lipid interaction is not nearly as frequent a phenomenon as cell-to-ion. In order for lipid molecules to be carried in our systems to tissue and thus to the cell surface, they are usually transported by being stuck onto the surface of large protein molecules like serum albumin, or to specific carrier proteins termed "chaparone proteins".

Hormones, specifically steroid hormones (which are chemically based on the large lipophilic molecule of cholesterol) are carried on protein complexes to cells and then cross the membrane freely. Once inside, they act on control proteins that are directly attached to the surface of DNA, and they subsequently affect the activation of specific protein synthesis pathways, and thereby modify cell biochemical behavior.

Another way in which phospholipids affect how transport proceeds across the cell membrane involves something called a "second messenger" system. Some cell signals that, like steroid hormones need to interact with the intracellular chemistry, arrive as non-lipophilic molecules such as short peptide chains. Such hormones can only reach to the cell surface but cannot penetrate. Instead, cell surface receptors exist, which are triggered by the hormone-receptor interaction. The intracellular component of these membrane proteins typically catalyzes a chemical reaction that releases a stream of signal molecules within the cytoplasm. These signal molecules, in turn, trigger the modifications to cellular chemistry and protein synthesis. One (of several) of these second messenger systems involves the use of specific phospholipids as the starting material in this cascade of events. This is an example, not exactly of phospholipid having a role in the control of MOLECULES across the cell membrane, but actually of the SIGNAL FUNCTION that crosses the membrane as a hand-off between multiple molecules!

...I hope that helps!

Answer 2

Due to its polar nature, the head of a phospholipid is hydrophilic (attracted to water); the nonpolar tails are hydrophobic (not attracted to water). When placed in water, phospholipids form a bilayer, where the hydrophobic tails line up against each other, forming a membrane with hydrophilic heads on both sides extending out into the water. This allows it to form liposomes spontaneously, or small lipid vesicles, which can then be used to transport materials into living organisms and study diffusion rates into or out of a cell membrane. This membrane is partially permeable, very flexible, and has fluid properties, in which embedded proteins and phospholipid molecules are constantly moving laterally across the membrane because of the forces generated by their vibrations. Such movement can be described by the Fluid Mosaic Model, which describes the membrane as a "mosaic" of lipid molecules that act as a solvent for all the substances and proteins within it, so proteins and lipid molecules are then free to diffuse laterally through the lipid matrix and migrate over the membrane.

Answer 3

First answer was great information, however I didn't think it answered the question. The role of phospholipids changes depending on the atom/molecular make-up of an object - but the above copied and pasted definition sums it up .

Answer 4

Biology and Behavioral Sciences ,and instabilities ,bifurcations ,and fluctuations in chemical systems