Cell Membrane

Phospholipids

• Essential for membranes
• contains two fatty acids linked to glycerol
• Amphipatic - contains both hydrophobic and hydrophilic molecules
• In water environment hides hydrophobic tails and expose hydrophilic heads
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Plasma Membrane

Cholesterol

• Contains polar (OH) head and non-polar tail
• Area of carbon rings making it amphipatic molecule
• Slows flow on outside of membrane helping separate inside and outside of membrane
• harder for water soluble molecules to pass through

Movement of Membrane

• Lateral Diffusion - side to side fast movement essential to allow diffusion of proteins attached to membrane
• Rotation - not essential
• Flip-Flop - very rare , change of phospholipid from one layer to the other

Membrane Protein Functions

• Hormone binding site
• Transport information across membrane
• Enzymes
• Electron carriers
• Channels - transport cargo across membrane passively

Diffusion

• Passive movement of particles from high to low concentration areas due to random movement of particles
• Efficient diffusion requires- maintenance of concentration gradient, large surface area, thin structures
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Osmosis

• Passive movement of water molecules from region of low solute concentration to region of high solute concentration through semipermeable membrane
• Isotonic solution - concentration inside and outside are equal
• Hypotonic solution - lower solute concentration outside cell
• Hypertonic solution - higher solute concentration outside cell
• Passive movement of water molecules from region of low solute concentration to region of high solute concentration through semipermeable membrane
• Isotonic solution - concentration inside and outside are equal
• Hypotonic solution - lower solute concentration outside cell
• Hypertonic solution - higher solute concentration outside cell
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Active Transport

• Uses ATP
• Protein pumps in membrane
• Movement against concentration gradient
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Endocytosis and Exocytosis