EXSC%223:%Week%of%8/29/16%%Notes%from%the%textbook%Ch.%3.3-3.5%3.3#Passive#membrane#transport#is#diffusion#of#molecules#down#a#concentration#gradient#• Passive%transport%o Diffusion%§ Tendency#of#molecules#or#ions#to#move#from#an#area#where#they#are#in#high#concentration#to#an#area#where#they#are#in#low#concentration#§ Move#down/along#the#concentration#gradient#§ Random#motions#• Powered#by#intrinsic#kinetic#energy#• Collisions#cause#particles#to#go#in#random#directions#o Particles#scatter#and#disperse#§ Speed#of#diffusion#is#affected#by:#• Molecule#size#(smaller#molecules=faster#diffusion#rate)#• Temperature#(warmer#system=faster#diffusion#rate)#§ In#a#closed#container,#a#uniform#mixture#will#be#the#result#§ At#equilibrium#• Molecules#move#equally#in#all#directions#• No#net#movement#o Filtration#• Plasma#membrane#o Selectively#permeable#§ Lets#nutrients#in#§ Keeps#bad#substances#out#§ Keeps#valuable#proteins#in#§ Lets#waste#out#o Unhealthy#cells#have#a#damaged#plasma#membrane#o Molecules#or#ions#can#diffuse#in#if:#§ Lipid#soluble#§ Small#enough#to#pass#through#membrane#channels#§ Assisted#by#a#carrier#molecule#• Simple%diffusion:#unassisted#diffusion#of#lipid#soluble#or#very#small#molecules#• Facilitated%diffusion:#assisted#diffusion#o Molecule#binds#to#proton#carriers#in#the#plasma#membrane#and#ferried#across#§ Transmembrane#integral#proteins#transport#polar#molecules#or#molecules#too#large#(ex:#sugars#and#amino#acids)#o OR%molecules#move#through#water#filled#protein#channels#§ Transmembrane#proteins#(integral#proteins)#usually#transport#ions#or#water#• Leakage%channels:#always#open#(ions#or#water#move#according#to#concentration#gradient)#• Gated%channels:#opened#or#closed#by#chemical#or#electrical#signals#• Osmosis:#diffusion#of#a#solvent#(usually#water)#through#a#membrane#o water#can#diffuse#through#water-specific#channels#called#aquaporins%(AQPs)#o occurs#when#water#concentration#differs#on#the#two#sides#of#the#membrane#o osmolarity:#total#concentration#of#all#solute#in#a#solution#• Tonicity:#ability#of#a#solution#to#change#shape#of#cells#by#altering#the#cells’#internal#water#volume#o Isotonic:#same#solute/water#concentration#inside#and#outside#of#the#cell#§ Cells#retain#normal#size#and#shape#§ Water#moves#in#and#out#of#the#cell#at#an#equal#rate#o Hypertonic:#solution#has#a#higher#concentration#of#solute#than#in#the#cell#§ Cell#shrinks#§ water#leaves#the#cell#o Hypotonic:#solution#is#dilute,#has#a#lower#concentration#of#solute#than#in#the#cell#§ Cell#becomes#bloated#and#lyse#(bursts)#§ Cell#takes#in#water##3.4#Active#membrane#transport#directly#or#indirectly#uses#ATP#• Active#transport#o Energy#required#o Moves#molecules#against#their#gradient#o Ex:#sodium-potassium#pump#§ 2#K+#in#§ 3#Na+#out#• Vesicular%transport#by#endocytosis#o Phagocytosis:#ingesting#of#solid#material#o Pinocytosis:#ingesting#of#fluid#material#o Steps:#§ Protein-coated#(usually#clathrin)#pit#forms#in#the#plasma#membrane#and#ingests#a#substance#§ Pit#pinches#off#and#the#substance#is#now#in#this#protein-coated#vesicle#inside#the#cell#§ The#protein#coat#falls#off#and#goes#to#the#plasma#membrane#to#be#recycled#(leaving#the#vesicle#uncoated)#§ Uncoated#vesicle#fuses#with#a#sorting#vesicle#(endosome)#§ The#fused#vesicle#may:#• Fuse#with#a#lysosome#• OR#deliver#contents#to#the#plasma#membrane#on#the#opposite#side#of#the#cell#(transcytosis:#move#substances#into#the#cell,#across,#and#eventually#out)##3.5#Selective#diffusion#establishes#the#membrane#potential#• Membrane%potential=#voltage#across#the#membrane#o Voltage=electrical#potential#energy#resulting#from#separation#of#oppositely#charged#particles#• Resting%membrane%potential:%-50%to%-100%millivolts%(mV)%o Polarized#o Inside#cell=negative#o Determined#by#K+#concentration#o Active#transport#of#K+#and#Na+#maintains#gradient#(sodium-potassium#pump)##Lecture%Notes%on%8/29%#Lipid#Rafts#• Specialized#area#of#plasma#membrane#• Important#to#localize#proteins#to#certain#areas#or#move#receptors#• Contain#higher#concentrations#of#cholesterol#and#sphingolipids#(saturated#fatty#acids)#to#maintain#a#more#rigid#structure#Transport#and#digestion#• Plasma#membrane#is#selectively#permeable#• Passive#transport#o Simple#diffusion#o Facilitated#diffusion#o Osmosis#• Active#transport#o Primary#active#transport#o Secondary#active#transport#• Vesicular#transport#o Endocytosis#o Exocytosis#o Osmosis#Diffusion#• Movement#from#high#to#low#concentration#• Passive%process%(does%not%require%energy)%• Ex:#dropping#a#tablet#in#a#beaker#of#water#and#the#contents#spread#throughout#the#beaker#until#there#is#a#uniform#substance#• Rate#of#diffusion#affected#by:#o Gradient:#big#contrast#in#gradient=faster#diffusion#rate#o Temperature:#high#temperature=faster#diffusion#rate#o Particle#size:#smaller#particles=faster#diffusion#rate#• Hydrophobic#membrane#prevents#diffusion#except#if#o Lipid#soluble#o Small#size#o Assisted#by#carrier#molecule#• Simple#diffusion:#lipid#soluble#(fatty#acids,#steroids),#small,#uncharged#molecules#• Facilitated#diffusion:#still#a#passive#process#because#the#substances#move#with#their#concentration#gradients#but#they#need#help#crossing#the#membrane#because#they#are#large,#charged,#or#lipid#insoluble#o Channel#proteins:#ex/#depolarization#(transport#Na+#and#K+)#o Carrier#proteins:#lipid#insoluble#solutes#(glucose,#amino#acids)#o Substances#move#through#according#to#concentration#gradient#o Carriers#can#become#saturated#• Osmosis%o Diffusion#of#water#across#a#semi-permeable#membrane#o Water#moves#through#aquaporins#o Occurs#when#concentration#of#water#is#different#on#opposite#sides#of#the#membrane#o Increased#concentration#of#a#solute#will#decrease#the#concentration#of#water#(due#to#displacement)#o Osmolarity:#total#concentration#of#solute#particles#in#solution#o When#2#solutions#differ#in#osmolarity,#water#will#move#along#a#concentration#gradient#to#reach#equilibrium#o When#hydrostatic#pressure#of#water=osmotic#pressure,#there#is#no#more#net#movement#by#osmosis#• Osmosis#vs#diffusion#o Diffusion#is#movement#of#solute#from#high#to#low#concentration#o Osmosis#is#the#movement#of#water#from#low#to#high#solute#concentration#when#separated#by#a#semipermeable#membrane#Effects#of#varying#solute#concentration#•