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BIO130 Exam Notes Chapter 10 and 11.docx

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Jane Mitchell

BIO130 Exam Notes Chapter 10Pgs 617624 The plasma membrane encloses cells and maintains the difference between cytosol and extracellular environmentmembraneenclosed organelles maintain the characteristic differences between contents of organelles in the cytosol Cells are fluid The Lipid Bilayer provides basic structure for cell membranes and can be easily found the lipid molecules spontaneously form a bilayer they are fluid individual lipid molecules can diffuse rapidly within their own monolayerAll the lipid molecules in a cell membrane are amphiphillic meaning that they have hydrophilic and hydrophobic ends Mostly phospholipids in membrane lipids 1 polar head and 2 hydrophobic tails Main phospholipids in animal cells are Phosphoglycerides composed of 3 carbon glycerol backbone linked via ester bonds Another phospholipid sphyngomyelin composed of sphyngoselong acyl chain with one amino group and two hydroxyl groups one free hydroxyl group forms the polar properties for the head Lipid bilayers in many cells contain cholesterol and glycolipids Chlosterol is found in large amount in eukaryotic plasma membranes and is sterol with hydroxyl group oriented near the polar head The lipid bilayer is a two dimensional fluidliposomes are bilayers that are made in the form of spherical vesiclesblack membranes or planar bilayers formacross a hole in partition between two aquous compartments to study motion of an individual lipid molecule you can stain it or you can modify it to carry a spin label whose spin creates a paramagnetic signal which can picked up by ESR electron spin resonance Process called flip flop The fluidity of a lipid bilayer depends on its composition and temperature for example bacteria and other organisms whose temperature fluctuates with their environment adjust the fatty acid composition of their membrane lipids meaning when temperature drops they syntheisze more cisdouble bonds between their fatty acids potentially avoiding decrease in bilayer fluidityChloseterol modulates the properties of lipid bilayers when mixed with phospholipids it enhances permeability properties It tightens the packing of lipid bilayers but does not make membranes any less fluid Despite their fluidity bilayers can form domains of different compositions Pgs629640 Membrane Proteins perform membranes specific tasks and thus gives each cell membrane its characteristic functional propertiesTransmembrane Proteins are amphiphillicwhile still in the endoplasmic reticulum the transmembranesegment of the protein is cleaved off and a GPIglycosolphos anchor is addedTransport vesicles eventually deliver the protein to the plasma membrane Those attached by GPI anchor can be cut off releasing them from the Membrane Only transmembrane proteins can function on both sides of the bilayer or transport molecules across it
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