CELL MEMBRANE

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Two types of boundaries separate: Cell Boundaries Every cell is surrounded by a liquid environment and has a liquid inside Two types of boundaries separate: Cell membrane (inner) Thin, flexible layer that surrounds all cells Cell wall (outer) Strong supporting layer outside the cell membrane Only in some organisms (plants, algae, fungi, prokaryotes) Porous

Phospholipids Cell membranes are mostly built from fat molecules called phospholipids Have a polar head and two nonpolar tails Polar heads  attracted to water Nonpolar tails  repelled by water Movie #1

Lipid Bilayer Because there is water inside and outside the cell, the phospholipids form a double layer called the lipid bilayer. Polar heads on outside, nonpolar tails on the inside Movie #2

Membrane Components Membranes also have proteins embedded in the bilayer act as tunnels or pumps across the membrane others protect the cell membrane Contains carbohydrates, usually attached to the proteins act as signals to other cells Contains cholesterol Stabilizes the membrane

Cell Membrane

Figure 7-12 The Structure of the Cell Membrane http://www.youtube.com/watch?v=ULR79TiUj80 Section 7-3 Outside of cell Inside (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains

Fluid Mosaic Model Lipid bilayer – double layer of molecules Figure 7-12 The Structure of the Cell Membrane Section 7-3 Lipid bilayer – double layer of molecules Lipids are a certain class of C-H molecules Do not like water ( think of oil + water) – the “tails” The “heads” are polar molecules Has proteins throughout Can have carbohydrate “ID tags” Moveable/fluid Selectively Permeable Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains

Cell Wall Cell wall – tough, porous boundary that lies outside the cell membrane; found in plant cells and in some bacteria but NOT in animal cells Allow water, gases, and other substances to pass through easily Most cell walls are made of carbohydrates and proteins - Specifically composed of cellulose

FUNCTION of Cell Membrane Regulates what goes in and what comes out of a cell Like a fence or a window screen Regulation depends on size, concentrations, and the type of molecule trying to get through Protects cell Supports cell, but also flexible Recognizes foreign material Communicates with other cells

What goes in and out? (Transport) Cell membrane is selectively permeable,  it lets some things in, but not other things Selection depends on… size (smaller get through easily) concentrations, & type of molecule trying to get through (lipid and nonpolar) Substances keep moving till there are ~ equal amounts of them on both sides of the membrane EQUILIBRIUM

Cell Membranes Must be able to take in raw materials and eliminate waste products Like a bouncer at a club

Permeability http://www. youtube. com/watch Do these get through? H+ or Ca++ CO2 K+, Cl- H2O Glycerol or ethanol (-OH) O2 Amino acids Glucose