Cell Membranes & Movement Across Them
Cell (plasma) membrane Cells need an inside & an outside separate cell from its environment cell membrane is the boundary IN OUT 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?
Lipids of cell membrane Membrane is made of inside cell phosphate attracts water lipid outside cell repels water
Semi-permeable membrane Need to allow passage through the membrane But need to control what gets in or out So what needs to get across the membrane? sugar aa lipid H 2 O salt waste 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 to all materials a cell needs to all waste a cell needs all products a cell needs to holes, or channels, in cell membrane allow material in & out inside cell outside cell sugar Haa 2 O salt waste lipid
Semi-permeable cell membrane But the cell still needs control membrane needs to be 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 both like water & like lipids bi-lipid membrane protein channels in bilipid 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???
Molecules move from high to low move from to concentration
Diffusion Move from to concentration passive transport
Diffusion Move from to 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
Diffusion through a channel Move from to sugar sugar sugar inside cell sugar sugar low sugar Which way will sugar move? high outside cell sugar sugar sugar sugar sugar sugar sugar
Facilitated diffusion Move from to concentration through membrane no energy needed through a (with help) no energy needed high low
Active transport Cells may need molecules to move against concentration situation need to pump uphill protein pump ATP
Transport summary ATP
Osmosis Movement of Water Across Cell Membrane
Osmosis is diffusion of water Water is very important, so we talk about water separately Osmosis across a semi-permeable membrane
Managing water balance Cell survival depends on balancing water uptake & loss
Managing water balance Balanced conditions no difference between cell & environment example: problem: none water flows across membrane equally, in both directions volume of cell doesn t change balanced
Managing water balance Freshwater a cell in example: freshwater problem:, swells & can burst water continually enters Paramecium cell solution: pumps water out of cell
Water regulation Contractile vacuole in Paramecium
Managing water balance Saltwater a cell in example: problem: plasmolysis in plants shrinking cell solution: saltwater
Any Questions??