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The functions of proteins in cell membranes. The fluid mosaic model is the clearest representation of a plasma membrane

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The functions of proteins in cell membranes. The fluid mosaic model is the clearest representation of a plasma membrane. It shows a phospholipid bilayer (with a hydrophilic phosphate head, and hydrophobic fatty acid 'tails'), with glycoproteins, glycolipids and numerous proteins distributed throughout. These membrane molecules have been synthesised by endoplasmic reticulum and distributed by Golgi apparatus. The plasma membrane acts as a boundary between intercellular and extra cellular space. It is a regulatory system, controlling the movement of molecules in to, out of and within the cell. The plasma membrane is selectively permeable. Throughout this essay I will refer mainly to the plasma membrane, however many of the statements are also true for organelle membranes. An example of the fluid mosaic model is shown below. There are two main protein membrane shapes, and these effect there function. Channel proteins (non-polar ? helix segments, which cross the whole lipid bilayer from cytoplasm to extra cellular space) create a channel through which the targeted molecule can pass. Pores (non-polar ? ...read more.


There are three types of transport proteins uniporter (binds to one molecule of solute at a time and transports it along the solute gradient), symporter/coporter (binds to two molecules at a time and uses the gradient of one solutes concentration to force the other molecule against its gradient ) and antiporter (binding to one molecule of solute (S1) outside the membrane, and one molecule (S1) on the inside. By using S2's gradient, we are able to transport S1 against its gradient). The above protein assists the movement of molecules across the partially permeable membrane by the following processes; facilitated diffusion, active transport and exocytosis. Facilitated diffusion moves molecules down the concentration, but needs to be assisted by a carrier protein. Active transport also requires a carrier transport protein, however this process goes against the concentration gradient and therefore requires ATP (energy) This is achieved by either altering the inclination of the binding site or altering the rate at which the protein changes shape to induce movement. ...read more.


The immune system would not function without these glycoproteins as there would be little ability to identify foreign cells. They play a unique role in cellular communication and signal transduction. Cell adhesion proteins are used to form cell junctions. This allows for tissues to be formed. Cell recognition and adhesion is used for growth and development. Homotypic adhesion proteins allow growth and regrowth to occur by attaching themselves to identical homotypic proteins (ligands) to form tissues, but need glycoproteins to first recognise an identical cell. Heterotypic recognition proteins allow sexual reproduction to occur with gamete cells. Without cell adhesion white blood cells could not function as they would be unable to attach themselves to alien cells. Alzheimer's disease is caused by poor adhesion of sypnases (cell junctions in the nervous system), which results in poor signalling between cells. Sources Bellevue community life science faculty. 2004. http://scidiv.bcc.ctc.edu/rkr/biology201 /lectures/pdfs/membranes201.pdf. Wikipedia. 2004. http://en.wikipedia.org/wiki/Main_Page. Saunders, Dr. N. 2004. http://www.biology.creative-chemistry.org.uk/documents/N-bio-04.pdf. Simpkins, J. Williams, J.I. 1992. Advanced Biology - 3rd Ed. Scot Print Ltd. Fullick, A. 2000. Heinemann ADVANCED Science BIOLOGY - 2nd Ed. Heinemann. WORD COUNT: 1002 ?? ?? ?? ?? Page 2 ...read more.

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