The Cell Membrane 2007-2008
Warm Up What would happen if you gave a patient an IV of pure water? a. Their blood cells would shrink. b. Their blood cells would burst. c. The patient would slowly become rehydrated. d. I would be promoted for my outstanding level of medical care.
What you need to know You need to predict how molecules move across membranes You need to know the difference between active and passive transport
Overview Cell membrane separates living cell from surroundings Controls traffic in & out of the cell selectively permeable hydrophobic vs hydrophilic Made of phospholipids, proteins & other macromolecules
Phospholipids Fatty acid tails hydrophobic Phosphate group head hydrophilic Arranged as a bilayer Phosphate Fatty acid Aaaah, one of those structure function examples
Movement across the Cell Membrane 2007-2008
Diffusion Diffusion movement from high low concentration
Diffusion Move from HIGH to LOW concentration passive transport no energy needed movement of water diffusion osmosis
Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids inside cell NH 3 lipid salt What molecules can NOT get through directly? polar molecules H 2 O ions outside cell sugar aa H 2 O salts, ammonia large molecules starches, proteins
Channels through cell membrane Membrane becomes semi-permeable with protein channels specific channels = specific materials inside cell H 2 O aa sugar NH 3 salt outside cell
Facilitated Diffusion Diffusion through protein channels channels move specific molecules across cell membrane no energy needed open channel = fast transport low facilitated = with help high The Bouncer
Active Transport Cells may need to move molecules from low to high concentration protein pump used costs energy (ATP) low conformational change ATP high The Doorman
Active transport Many models & mechanisms ATP ATP antiport symport
Getting through cell membrane Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids high low concentration gradient Facilitated transport through a protein channel high low concentration gradient Active transport diffusion against concentration gradient low high uses a protein pump requires ATP ATP
Transport summary simple diffusion facilitated diffusion active transport ATP
How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = cellular eating pinocytosis = cellular drinking exocytosis exocytosis
The Special Case of Water Movement of water across the cell membrane 2007-2008
Osmosis is diffusion of water Diffusion of water from high concentration of water to low concentration of water Across membrane
Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water hypotonic hypertonic net movement of water
Managing water balance Cell survival depends on balancing water uptake & loss freshwater balanced saltwater
Water regulation Contractile vacuole in Paramecium ATP
Osmosis.05 M.03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell
Exit Ticket: Justify Why! An animal cell is placed in a saltwater solution. Predict what might happen to the cell when exposed to this solution. Describe the solution too. Is it hypertonic, hypotonic, or isotonic?
Any Questions??