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Traffic control in cells… Who’s the man (or woman)??
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“attracted to water” “repelled by water”
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Arranged as a Phospholipid bilayer
Serves as a cellular barrier / border between the living cell and the aqueous (water) environment(s). sugar H2O salt polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads waste lipids
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Permeability to polar molecules?
Membrane becomes semi-permeable via protein channels specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3
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Cell membrane defines cell
Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick Controls traffic in & out of the cell allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar)
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Cytoplasm Phospholipids
1972, Singer & Nicolson proposed Fluid Mosaic Model Glycoprotein Glycolipid Extracellular fluid Phospholipids Transmembrane proteins Cholesterol Peripheral protein Filaments of cytoskeleton Cytoplasm
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Many Functions of Membrane Proteins
“Channel” Outside Plasma membrane Inside Transporter Enzyme activity Cell surface receptor “Antigen” Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made. Cell surface identity marker Cell adhesion Attachment to the cytoskeleton
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Why are cell membranes described in what is called the “Fluid Mosaic Model”?
Explain what Singer & Nicholson meant by this in 1972.
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But how do cells move things in and out?
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