transport through cell membranes
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Transport through cell membranes. Are you covered in skin?. Are you REALLY covered in skin?. Why do you have openings in your skin?. Doesn’t work like this. - PowerPoint PPT PresentationTRANSCRIPT
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Transport through cell membranes
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Are you covered in skin?
Are you REALLY covered in skin?
Why do you have openings in your skin?
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Doesn’t work like this
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Molecules are always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always, always
moving.
(So where are they going?)
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How do the molecules “know” how to spread out? Are they doing it on purpose?
http://concord.org/stem-resources/diffusion-osmosis-and-active-transport
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Each individual molecule moves randomly, bumping into whatever is in its path.
If all the molecules start out close together, what’s the likelihood of a molecule bumping its
way out of the pack compared to randomly staying with everyone else?
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Formal Vocabulary
• Molecules diffuse from areas of high concentration to areas of low concentration.
• They move down a concentration gradient.
• This is a passive process. (It happens on its own – we didn’t have to spend any energy to move things around.)
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So how do we get things in and out of cells?
Can’t forget about that membrane made of phospholipids . . .
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Phospholipid tails hate water. But why?
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A quick review
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I’m a happy nonpolar molecule with equally shared electrons!
Crap . . . Lesson: Nonpolar stuff (like lipid tails) hates water.
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But what if you’re not polar?
O2 – both atoms are equally attractive to electrons
CO2 – both sides are equally attractive to electrons
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Molecules that diffuse through cell membranes
• Oxygen (O2)
• Carbon dioxide (CO2)
. . . That’s about it.
Everyone else needs a channel.
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Facilitated diffusionYou need a channel if you’re . . .
Charged (ion)
Big Polar
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Your Very Own Channel!
http://phet.colorado.edu/en/simulation/membrane-channels
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Water is curious . . .
‘
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If there are other molecules dissolved in the water, not all of the water molecules are free to diffuse – some are too busy being attracted to the dissolved stuff.
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Osmosis
• http://www.concord.org/~btinker/workbench_web/models/osmosis.swf
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Ooops . . .
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Red Blood Cells Shriveling
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Variations on a Theme
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Big Stuff
• What if you want to take in something so large, it won’t fit through a channel?
• What if you want to get rid of something so large, it won’t fit through a channel?
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Endocytosis
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AS Biology, Cell membranes and Transport
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Exocytosis
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It really does happen . . .
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The Grand Chase
http://www.youtube.com/watch?v=JnlULOjUhSQ