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Cell Membranes & Movement Across Them
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Lipids of cell membrane
Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer Membrane is semi-permeable “attracted to water” Hydrophilic phosphate inside cell outside cell Fatty acid Hydrophobic “repelled by water”
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Passive Transport – No Energy
Diffusion Osmosis Facilitated Diffusion
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Molecules move from high to low
Diffusion move from HIGH to LOW concentration Movement from high concentration of that substance to low concentration of that substance.
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Diffusion Move from HIGH to LOW concentration diffusion
passive transport no energy needed EXAMPLE diffusion
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Crossing the cell membrane
What molecules can get through the cell membrane directly? Oxygen, fats and oils can pass directly through inside cell outside cell lipid salt waste but… what about other stuff? sugar aa
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Cell membrane channels
Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar salt outside cell waste
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Facilitated Diffusion
Move from HIGH to LOW through a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar
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Simple vs. facilitated diffusion
simple diffusion facilitated diffusion O2 inside cell outside cell sugar inside cell outside cell protein channel sugar
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Osmosis diffusion of water
Water is very important, so we talk about water separately diffusion of water
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Osmosis Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane
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Active transport Cells may need molecules to move from LOW to HIGH concentration requires energy (ATP) ATP Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer.
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ANALOGY: ENERGY NEEDED: Active Transport NO ENERGY NEEDED: Diffusion
Osmosis Facilitated Diffusion ENERGY NEEDED: Active Transport
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Endocytosis and Exocytosis is how very large molecules (such as food, wastes and some protiens) get into and out of the cell Food is moved into the cell by Endocytosis Wastes are moved out of the cell by Exocytosis animation
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Cystic Fibrosis CFTR Protein Mutations in the DNA
Doesn’t make it to membrane Channel won’t open How is homeostasis affected? Cystic Fibrosis Video (5:08-6:32)
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