Cell Membranes & Movement Across Them 2006-2007
Cell (plasma) membrane Cells need an inside & an outside separate cell from its environment cell membrane is the boundary IN food sugars proteins fats salts O 2 H 2 O OUT waste ammonia salts CO 2 H 2 O products cell needs materials in & products or waste out
Building a membrane How 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!!
Lipids of cell membrane Membrane is made of phospholipids phospholipid bilayer inside cell phosphate attracted to water lipid outside cell repelled by water
Semi-permeable membrane Need to allow passage through the membrane But need to control what gets in or out membrane needs to be semi-permeable So what needs to get across the membrane? sugar aa lipid H 2 O salt NH 3 So how do you build a semi-permeable membrane?
Phospholipid bilayer What molecules can get through directly? inside cell waste lipid salt fats & other lipids can slip directly through the phospholipid cell membrane, but outside cell sugar aa H 2 O what about other stuff?
Permeable cell membrane Need to allow more material through membrane needs to be permeable to all materials a cell needs to bring in all waste a cell needs excrete out all products a cell needs to export out holes, or channels, in cell membrane allow material in & out inside cell sugar Haa 2 O lipid outside cell salt waste
Semi-permeable cell membrane But the cell still needs control membrane needs to be semi-permeable specific channels allow specific material in & out inside cell H 2 O aa sugar outside cell waste salt
How do you build a semi-permeable cell membrane? channels are made of proteins proteins both like water & like lipids protein channels in bi-lipid membrane
Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane
Movement through the channel Why do molecules move through membrane if you give them a channel??? Brownian Motion
Molecules move from high to low Diffusion move from HIGH to LOW concentration With the concentration gradient
Diffusion Move from HIGH to LOW concentration passive transport no energy needed
Simple Diffusion: diffusion across a membrane Move from HIGH to LOW inside cell low fat fat fat fat fat fat Which way will fat move? high outside cell fat fat fat fat fat fat fat fat
Facilitated Diffusion: through a channel Move from HIGH to LOW sugar sugar sugar inside cell sugar sugar low high sugar Which way will sugar move? outside cell sugar sugar sugar sugar sugar sugar sugar
Diffusion Move from HIGH to LOW concentration through membrane simple diffusion no energy needed through a protein channel facilitated diffusion (with help) no energy needed high low
Active transport Cells may need molecules to move against concentration difference need to pump uphill from LOW to HIGH using ATP protein pump requires energy ATP ATP
Transport summary diffusion facilitated diffusion active transport ATP
Osmosis Movement of Water Across Cell Membrane 2006-2007
Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane
Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater
Keeping water balance Comparing the cell with its environment Isotonic: equal amounts of water and solutes Hypotonic: more water less solutes Hypertonic: less water more solutes Hypotonic isotonic hypertonic
Managing water balance isotonic no difference between cell & environment example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn t change balanced
Managing water balance Hypotonic (Freshwater) a cell in fresh water example: Paramecium problem: gains water, swells & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell freshwater
Controlling water Contractile vacuole in Paramecium
Managing water balance Hypertonic (Saltwater) a cell in salt water saltwater example: shellfish problem: lose water plasmolysis in plants shrinking cell solution: take up water
Ice Fishing in Barrow
Any Questions?? 2006-2007