Chapter 5: Membrane Structure And Transport PDF

Membrane Structure And Transport Biological membranes : - > - Biological membranes, orcellmembranes aremainly made of Phospholipidbilayer > Phospholipids Waterrepelling (hydrophobic) Parts havebothWaterLoving (hydrophilic) and...

Membrane Structure And Transport Biological membranes : - > - Biological membranes, orcellmembranes aremainly made of Phospholipidbilayer > Phospholipids Waterrepelling (hydrophobic) Parts havebothWaterLoving (hydrophilic) and r - > - The hydrophilicpartsfaces inwardand hydrophobic partsfaces outward > membranes also - containproteins and carbohydrates,each amounts ofthem canvary Lipids(phospholipids) · Phospholipids- > key components ofcell membranes and containPhosphategroup · unlikefats, which3 fatty acids attackedto glycerol, Phospholipids haveafatty & acids andPolarPhosphategroupinsteadofthirdfatty acido Phospholipids are comphipathic - : · Hydrophilic heads- > Phosphate group that attract water eyces+3fatty acidTrelyceride(fat) on · Hydrophobic heads->fatty acidchains that repellated · Incell membrane Phospholipids arrangethemselves so thatthe hidophilicheads face outwardtowardwater · Whilehydrophobictails face inwardaway fromwaterforming phospholipid bilayermainstructure ofcellmembranes Fluid - mosaic model - The membrane is describedas a mosaic composed of Lipids, proteins, and carbohydrate molecules · - Itdisplays fluid-likeproperties, allowing Lipids and proteins to move relativeto one anotherwithinthe membrane· - The membrane is fluid in nature, with it's components, including Phospholipids andProteins , constantly inmotion - These molecules primarily more Laterally withina Leaflet : - iedto structures oneitherside ofthe membrane making themrelatively stationary However, some proteins are an Phospholipids can undergo flip-flop movement(transverse diffusion) between Leaflets, butthis process is showerandrequires - energy  Proteins bound to membranes trans -while Phosphocipias bilaterservesas thefundamental structure of the cellularmembrane, the proteincomponents is responsibleformost of it's otherfunctions· ways proteins can associatewith membrane: - Integralmembrane Proteins(intrinsicmembrane Proteins) - : >TransmembraneProteins- more regionsthat are physically > Proteins have for embeaded withinthe hydrophobicarea of Phospholipia bilayers > Proteins are covalently attached to Lipidmolecule that is linkedto aminoaciasidechainwithinProtein > Lipidanchors- - Peripheralmembrane Proteins(extrinsicmembrane Proteins) :- - They arenon-covalently attackedwithregions of integral membraneproteins that extendfromthemembrane, orthey bindto the polanheadgroups of Phospholipids. Membranes are semi-fluid · · Biomembranes display fluidity fluidity- > individualmolecule stays closely associated Whilestillbeing able to morefreely withinthemembraneo · me Biomembranes are semifluid- as most Lipids can rotatefreely around theirlong axes and more laterally within the membrane Leaf let, allowing for20 motion · Rotationaland loteral movement helps keepthefatty acidtails withinhydrophobic interiorand doesn't require energy , · At37, Lipid molecules canexchangepositions withtheirneighbors approximatelydo milliontimes Perseconds In contrast to these rotational and lateral movements, the"flip-flop" of Lipids from1 Leafletto the opposite Leaflet · doesn't happenspontaneously · This process requires theenzymeflippage, it utilizes energyfromATP hydrolysis to transport Lipidfrom1 Leaflet to another Plasma membrane fluidity Plasmamembranes - Possess a fluid nature, characterized by movement ofmoleculeslike Phospholipids&proteins - Increasedfluidity allows forgreater movement of Plasma membrane molecules, whilereducedfluidityresults in a Si more rigid membrane. - In a more fluidPlasma membrane, the attractions betweenmolecules areweakercomparedto those in rigid membrane· - Aligiastructurewill havea highermelting temperatures  Factors affecting fluidity Phospholipids significantly influencethe >The biochemical propertiesof - fluidity of Phospholipid bilayed Lengthoffatty acttrils : - shorten Longer Thesetails can > - rangefrom14 to 24 carbonatoms· >shorteracytails are less - likely to interact withanotheracyLtails resultinginincreasedfluidity of the membrane· fluid rigid Precenseofdouble bonds in acystails (unsaturated) : fluid Viscons >The - presenceofa doublebond introduces a kink infatty act tail. A g8888888 Which it blocks interactions between neighboringtails and enhances > - 88808320000830320 000 0 00 0 00 00 B unsaturated histkarbon saturated hydrocarbons the fluidityofthe bilayer tails With kinks Presence ofCholestrol: - It's a short > - and neid molecule produced by animal cells & affects > cholestplass fle in stabilizing membranes, with it's - varying based ontemperature. > - temperatures, cholestrol reduces thefluidityofthe membrane· At higher >A - lowertemperatures, it increasesfluidity and help preventthemembranefromfreezing. · Experiment on lateral transport frye and exidinperformedan experiment to Coniformthe Lateral movement of membrane Proteins· · They fused mouseand humanCeLLs andtreatedthemof temperatures of o'c and 37 Co % · The mousemembrane ProteinH-2was fluorescently Labeledo ° · Ato C, the Label remainedon the mouse side: · At37, the Labelspread across the entire cello Not all Integral membrane proteins can move The movementof membrane Proteins canbe limiteddepending on - Cell type,With10-70% Potentially Limited in theirmobility. attachment - Integralmembraneproteins may beanchored to components ofcytoskeleton, which blockstheirLateralmovement - MembraneProteins can be connected to external molecules,suchas networkof proteins that constitutes the extracellularmotixo