Cell Membrane

Function Protects cell Allows for passage of certain materials in and out of cell

Structure Double layer of phospholipids Polar heads, nonpolar fatty acid tails Proteins help materials move through Carbohydrates attach to proteins for cell identification

Fluid Mosaic Model Describes the arrangement of molecules making up the cell membrane Based on two characteristics: Flexibility- phospholipids move and slide past each other (fluid) Appearance- variety of molecules scattered throughout membrane (mosaic)

Selective Permeability Allows some (but not all) materials to cross Important to maintain homeostasis within the cell Passage through membrane varies, but in general: Small nonpolar molecules easily pass through Small polar molecules transported via proteins Large molecules moved through in vesicles

Transport of Materials Passive transport- passage of materials does not require energy Diffusion Osmosis Facilitated diffusion Active transport- requires energy Endocytosis

Diffusion Movement of molecules from high to low concentration Concentration gradient- difference in concentration of a substance throughout the solution Dynamic equilibrium- concentration is uniform throughout solution (equilibrium), but molecules are always moving (dynamic) Small lipids and other nonpolar molecules diffuse across

Osmosis Movement of water molecules from high to low concentration Isotonic solution- same concentration of dissolved particles as cell Hypertonic solution- has a higher concentration of dissolved particles than cell; cell shrivels Hypotonic solution- lower concentration of dissolved particles than cell; cell expands and bursts

Facilitated Diffusion Diffusion of molecules across the membrane through transport proteins Still no energy required… passive transport

Active Transport Requires energy to move molecules through cell membrane Molecules move against concentration gradient (from low to high concentration) Uses transport proteins Span membrane Use chemical energy (typically ATP) to move substance

Endocytosis Process of taking in liquids/other large molecules by engulfing them in the cell membrane The resulting vesicle then fuses with a lysosome to be broken down

Endocytosis Phagocytosis “cell eating” Pinocytosis “cell drinking” Exocytosis- opposite of endocytosis Release of substance out of cell