2Cell (plasma) membrane separate cell from its environmentcell membrane is the boundaryINfoodsugarsproteinsfatssaltsO2H2OOUTwasteammoniasaltsCO2H2Oproductscell needs materials in & products or waste out
6Building a membraneHow do you build a barrier that keeps the watery contents of the cell separate from the watery environment?What substance do you know that doesn’t mix with water? FATS LIPIDS oil & water don’t mix!!
7Lipids of cell membrane Membrane is made of phospholipidsphospholipid bilayerphosphate“attracted to water”inside celloutside celllipid“repelled by water”
8Semi-permeable membrane Need to allow passage through the membraneBut need to control what gets in or outmembrane needs to be semi-permeableSo what needs to get across the membrane?sugaraalipidH2OsaltNH3So how do you build a semi-permeable membrane?
9Phospholipid bilayer What molecules can get through directly? *small moleculesfats & other lipidscan slip directly through the phospholipid cell membrane, but…what about other stuff?lipidinside celloutside cellsaltwastesugaraaH2O
10Permeable cell membrane Need to allow more material throughmembrane needs to be permeable to…all materials a cell needs to bring inall waste a cell needs excrete outall products a cell needs to export outinside cellaaH2Osugarlipid“holes”, or channels, in cell membrane allow material in & outsaltwasteoutside cell
11Semi-permeable cell membrane But the cell still needs controlmembrane needs to be semi-permeablespecific channels allow specific material in & outinside cellH2Oaasugarsaltwasteoutside cell
12How do you build a semi-permeable cell membrane? channels are made of proteinsproteins both “like” water & “like” lipidsbi-lipidmembraneprotein channels in bi-lipid membrane
13Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membraneDonuts!Each transport protein is specific as to the substances that it will translocate (move).For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane.These channel proteins allow fast transport.For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion.
14Most cell membranes are composed principally of DNA and ATPproteins and lipidschitin and starchnucleotides and amino acids
15Most cell membranes are composed principally of DNA and ATPproteins and lipidschitin and starchnucleotides and amino acids
16Movement through the channel Why do molecules move through membrane if you give them a channel???
17Molecules move from high to low Diffusionmove from HIGH to LOW concentrationMovement from high concentration of that substance to low concentration of that substance.
18Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed
25Active transportCells may need molecules to move against concentration differenceneed to pump “uphill”from LOW to HIGH using ATPprotein pumprequires energyATPPlants have nitrate & phosphate pumps in their roots.Why?Nitrate for amino acidsPhosphate for DNA & membranesNot coincidentally these are the main constituents of fertilizer.ATP
30OsmosisOsmosisdiffusion of water from HIGH concentration of water to LOW concentration of wateracross a semi-permeable membrane
31Normally, in the process of osmosis, the net flow of water molecules into or out of the cell depends upon differences in the1. concentration of water molecules inside and outside the cell2. concentration of enzymes on either side of the cell membrane3. rate of molecular motion on either side of the cell membrane4. rate of movement of insoluble molecules inside the cell
32Keeping water balanceCell survival depends on balancing water uptake & water lossfreshwaterbalancedsaltwater
33Managing water balance Balanced conditionsno difference between cell & environmentexample: bloodproblem: nonewater flows across membrane equally, in both directionsvolume of cell doesn’t changebalanced
34Managing water balance Freshwatera cell in fresh waterexample: Parameciumproblem: gains water, swells & can burstwater continually enters Paramecium cellsolution: contractile vacuolepumps water out of cellfreshwater
35Controlling waterContractile vacuole in Paramecium
36Managing water balance Saltwatera cell in salt waterexample: shellfishproblem: lose waterplasmolysis in plantsshrinking cellsolution: take up watersaltwater