User:Jwiggler/Semipermeable membrane

Ideas for the paper: add hemodialysis section, add osmostic stress response of cells (or at least semipermeable membrane leads to osmotic stress), osmotic pressure link with short explanation. Cellular permeability and antibiotics? Maybe add what is permeable to cell membrane etcetera.

Excerpt from Semipermeable membrane with possible locations for additions

Goals: write and add three paragraphs (osmotic stress, dialysis tubing, and the intro to artificial membranes), add wiki connections and citations for each, and include new images into the paper

optional goal: after including sections, clean up some odd sentences and phrases throughout the rest of the page.

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Biological membranes[edit]

An example of a biological semi-permeable membrane is the lipid bilayer, on which is based the plasma membrane that surrounds all biological cells. A group of phospholipids (consisting of a phosphate head and two fatty acid tails) arranged into a double layer, the phospholipid bilayer is a semipermeable membrane that is very specific in its permeability. The hydrophilic phosphate heads are in the outside layer and exposed to the water content outside and within the cell. The hydrophobic tails are the layer hidden in the inside of the membrane. Cholesterol molecules are also found throughout the plasma membrane and act as a buffer of membrane fluidity. The phospholipid bilayer is most permeable to small, uncharged solutes. Protein channels are embedded in or through phospholipids, and, collectively, this model is known as the fluid mosaic model. Aquaporins are protein channel pores permeable to water.

Cellular communication[edit]

Information can also pass through the plasma membrane when signaling molecules bind to receptors in the cell membrane. The signaling molecules bind to the receptors, which alters the structure of these proteins. A change in the protein structure initiates a signalling cascade. The G protein-coupled receptor signalling provides is an important subset of such signalling processes.

Osmotic stress[edit][edit] (add links to osmotic stress and osmotic pressure)

Due to having a semipermeable membrane, cells experience osmotic pressure in different solutions. The lipid bilayer is permeable to water and some hydrophobic molecules, but most proteins and ions cannot pass through. Water will flow outwards or inwards to balance out concentrations, which can kill cells.

Artificial membranes[edit]

Paragraph of intro

Reverse-osmosis

The bulk flow of water through a selectively permeable membrane because of an osmotic pressure difference is called osmosis. This allows only certain particles to go through including water and leaving behind the solutes including salt and other contaminants. In the process of reverse osmosis, water is purified by applying high pressure to a solution and thereby push water through a thin-film composite membrane (TFC or TFM). These are semipermeable membranes manufactured principally for use in water purification or desalination systems. They also have use in chemical applications such as batteries and fuel cells. In essence, a TFC material is a molecular sieve constructed in the form of a film from two or more layered materials. Sidney Loeb and Srinivasa Sourirajan invented the first practical synthetic semi-permeable membrane. Membranes used in reverse osmosis are, in general, made out of polyamide, chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small molecules that cannot be filtered. Cellular communication[edit]

Dialysis tubing

Insert paragraph here

Other types[edit]

Other types of semipermeable membranes are cation-exchange membranes (CEMs), anion-exchange membranes (AEMs), alkali anion exchange membranes (AAEMs) and proton-exchange membranes (PEMs).