Plasma Membrane

Cell membranes Cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

vocabulary • • • • • • • •

Cell membranes Phospholipid bilayer Diffusion Osmosis Equilibrium Isotonic Hypertonic Facilitated diffusion

• Hypotonic • Active transport • Concentration

Phospholipids • Hydrophilic (polar) head and hydrophobic (nonpolar) fatty acid tail. • Interaction with water cause the phosholipids to create a bilayer, with fatty acid hydrophobic tails inside the bilayer and hydrophilic groups exposed to the water.

• Unique design of plasma membrane allows the cell to be semipermeable. This is important for the cell to function.

Three ways of getting in and out of the cell through the membrane 1. Simple diffusion such as water osmosis (Zero energy required) 2. Carrier-facilitated diffusion- use of protein carriers to cross over (zero energy required) 3. Active transport- requires free energy in the form of a chemical bond or pump

Concentration & Diffusion • The concentration of a solution is the mass of a solute in a given volume of solution. • In diffusion, particles move from an area of high concentration to low concentration. • When the solute is evenly distributed the solution has reached equilibrium.

Diffusion • Zero Energy is required • Cell does not have to use any ATP • Random movement of particles • Ends when equilibrium is reached • Simple diffusion

Osmosis • Water molecules are polar • Not expected to pass through lipid bilayer • Chemists recently discovered ‘aquaporins’ • Channels made of proteins • Allow for water molecules to pass into cell. • osmosis

Hypertonic and Hypotonic • Water will tend to move across membranes until equilibrium is reached; the concentration of water will be the same on both sides= isotonic • If solute is more concentrated=hypertonic – “above strength”

• If solute is less concentrated=hypotonic – “less strong”

Penicillin • Antibiotic works by depending upon osmosis • Penicillin inhibits an enzyme with which many bacteria produce that strengthens their cell wall • The weakened cell wall cannot withstand osmotic pressure • Gradually the wall becomes so weak it bursts.

Facilitated Diffusion • Cell membranes have protein molecules embedded into them which create channels for specific substances. • Fast and specific for that molecule • Net movement of molecules across membrane only occurs if the concentration is higher on one side than another. • No energy required • Carrier-facilitated diffusion-

Active Transport • Materials are moved against the concentration gradient • Requires energy • Transport proteins “pumps” found in the cell membrane

Review 1.

What is the term used to describe the cell membrane which indicates the ability to only let some particles in? 2. The main role of the cell membrane is to? 3. What type of molecule is embedded in the cell membrane to allow large molecules to pass through by active transport? 4. Osmosis is the mov’t of what across a membrane?