Traffic control in cells… Who’s the man (or woman)??

“attracted to water” “repelled by water”

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

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

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)

Cytoplasm Phospholipids 1972, Singer & Nicolson proposed Fluid Mosaic Model Glycoprotein Glycolipid Extracellular fluid Phospholipids Transmembrane proteins Cholesterol Peripheral protein Filaments of cytoskeleton Cytoplasm

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

Why are cell membranes described in what is called the “Fluid Mosaic Model”? Explain what Singer & Nicholson meant by this in 1972.

But how do cells move things in and out?