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Lecture 2

Lecture 2 - Membrane and Membrane Structure - January 10.docx

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BIOL 2021
Patricia Lakin- Thomas

January 10, 2012 Lecture 2: Membrane and Membrane Structure Function of Membranes  Barrier to water soluble molecules o This is because of the non-polar interior bilayer  Separate inside from outside o Cell vs. environment o Organelle vs. cytosol  Maintain ion gradient o Energy conversion (i.e. mitochondria for ATP production) o Signalling  Signalling o Plasma membrane receptors o Relay of signals from inside the cell Structure of Membranes  Transmembrane proteins go across lipid bilayer ~5nm o 50:50 lipid to protein by weight (it is noted that by function, this can change exponentially)  Held together by NONCOVALENT interactions  Lipids: o Fatty molecules o Amphiphillic – two natures hydrophillic at one end and hydrophobic at the other o Main categories of membrane lipids in animal cells:  Phospholipids  Phosphoglyceride + sphingo myelin  Phosphoglyderide is a glycerol backbone and two fatty acids [usually one unsaturated and one saturated] + head group  4 major phospholipids in the mammalian plasma membrane (PM) o Phosphoglycerides (Look these up, be able to recognize them)  Phosphotidyl ethanolamine  Phosphotidyl Serine  Phosphotidyl Choline  Sphingomyelin = sphingosine + fatty acid + choline head group  Glycolipids  Sphingosine backbone  Animal glycolipids Sphingosine + fatty acid + sugars  Bacterial and plant glycolipids Glycerol backbone + 2 Fatty acids + sugars  E. Coli – no glycolipids...  ONLY ON THE OUTER SURFACE OF CELLS o Preferable orientation is cylindrical which leads to a bilayer  spontaneous formation in water. Two leaflets (each leaflet is half)  Minimizes free energy  It is noted that a cone form is possible as well, this is for micelles o Mobility  Lateral diffusion – back and forth  Flexion of tails  Rotation  Flip-flop – rare unless energy is input o Membrane fluidity  What keeps the cell in shape?!  Cell shape is determined by the cytoskeleton  Regulation of Fluidity  Depends on temperature and composition (fatty acid content) o Cis-double bonds make it more fluid and saturation makes it less fluid o Low temperature also makes the membrane less fluid o THUS:  High fluidity:  High temperature  Cis-fatty acids
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