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Cell Membrane Cell Membrane Selective Permeability Cell membrane notes Introduction • Plasma (cell) membrane > thin barrier > controls traffic into and out of the cell > basic method of transport in unicellular organisms > selectively permeable Oct 119:12 AM 1 Cell Membrane STRUCTURE • main macromolecules in membranes: > lipids & proteins, some carbohydrates > Phospholipids: – Hydrophobic fatty acid tails (sheltered from water) – the hydrophilic phosphate groups/ heads (interact with water) Oct 119:12 AM Oct 119:12 AM 2 Cell Membrane Membrane proteins help to regulate the movement of material in and out of the cell Membrane proteins Transport: Act as channels to help move molecules through the membrane Marker: Advertise the cell’s type Receptor: Bind with specific substances Enzyme: Assist chemical reactions Oct 119:16 AM Selective Permeability • Cell membranes help decide what goes in and out of the cell • This is known as selective permeability • We say that cell membranes are “selectively permeable” > Allows some things to go in and out of the cell but not other things • Easier for small nonpolar molecules • Hard for polar and ionic molecules Oct 119:16 AM 3