4.3 Membrane Structure

Membrane Function Surrounds all cells Regulates cell’s internal environment ◦ Maintains HOMEOSTASIS  Maintains the same conditions constant inside the cell, regardless of external conditions

Membrane Function Regulates what enters and exits the cells ◦ Selectively permeable  Only allows specific materials to pass over the membrane  Examples: spaghetti strainer & mosquito netting  Allows water & nutrients to enter the cell and wastes to leave the cell

Membrane Structure: 1. Phospholipids Phospholipid ◦ Lipid with…  2 fatty acids  1 glycerol  1 phosphate group  1 polar group ◦ Fatty acids are hydrophobic ◦ The rest of the phospholipid is hydrophilic

Membrane Structure 1. Phospholipids Form a bilayer ◦ Cell membrane has two layers of phospholipids ◦ Polar “heads” attracted to water, carbs, proteins outside the cell and in the cytoplasm  Face outward ◦ Non-polar “tails” not attracted to water  Face inward

Membrane Structure 2. Cholesterol Lipid ◦ Hydrophobic  Fits in with fatty acid tails of phospholipids Function: ◦ Keeps membrane from freezing or falling apart ◦ Helps “stabilize” membrane

Membrane Structure 3. Membrane Proteins Membrane proteins have: ◦ Hydrophobic regions & Hydrophilic regions ◦ These help membrane proteins STAY in membrane

Membrane Structure 3. Membrane Proteins Which color of the protein is hydrophilic? Hydrophobic?

Membrane Structure 3. Membrane Proteins Function: ◦ Recognize material & transport into or out of cell

Fluid Mosaic Model Describes the cell membrane: ◦ Phospholipids are always moving like a fluid membrane proteins make a pattern in the cell membrane

REMEMBER THIS…? What is concentration? ◦ The amount of particles in a particular area

Concentration gradient Concentration gradient: unequal distribution of particles (solute) in a solution Particles will move until the concentration is equal ◦ Dynamic equilibrium

Concentration Gradient What will happen?

Concentration Dynamic equilibrium!

Bozeman membrane 6uGgE 6uGgE