4.3 Membrane Structure4.3 Membrane Structure

Membrane FunctionMembrane FunctionSurrounds all cellsRegulates cell’s internal

environment◦Maintains HOMEOSTASIS

Maintains the same conditions constant inside the cell, regardless of external conditions

Membrane FunctionMembrane FunctionRegulates 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:Membrane Structure:1. Phospholipids1. PhospholipidsPhospholipid

◦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 StructureMembrane Structure1. Phospholipids1. PhospholipidsForm 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 StructureMembrane Structure2. Cholesterol2. CholesterolLipid

◦Hydrophobic Fits in with fatty acid tails of

phospholipids

Function:◦Keeps membrane from freezing or

falling apart◦Helps “stabilize” membrane

Membrane StructureMembrane Structure3. Membrane Proteins3. Membrane ProteinsMembrane proteins have:

◦Hydrophobic regions & Hydrophilic regions

◦These help membrane proteins STAY in membrane

Membrane StructureMembrane Structure3. Membrane Proteins3. Membrane ProteinsWhich color of the protein is

hydrophilic? Hydrophobic?

Membrane StructureMembrane Structure3. Membrane Proteins3. Membrane ProteinsFunction:

◦Recognize material & transport into or out of cell

Fluid Mosaic ModelFluid Mosaic ModelDescribes the cell membrane:

◦Phospholipids are always moving like a fluid membrane proteins make a pattern in the cell membrane

REMEMBER THIS…?REMEMBER THIS…?What is concentration?

◦The amount of particles in a particular area

Concentration gradientConcentration gradientConcentration gradient:

unequal distribution of particles (solute) in a solution

Particles will move until the concentration is equal◦Dynamic equilibrium

Concentration GradientConcentration GradientWhat will happen?

Concentration Concentration Dynamic equilibrium!

Bozeman membraneBozeman membranehttp://www.youtube.com/watch?v

=y31DlJ6uGgE