CELL MEMBRANE

Structure

·   Fluid mosaic (èmany different parts)

·   2 layers of lipids sandwiched together

·   hydrophilic head (polar)

·   2 hydrophobic tails

·   nonpolar & polar molecules don’t mix! (Think oil and water)

·   glycoproteins

General Function

·   Barrier

·   Several jobs

·   Selectively permeable

o What can pass and what can’t?

Across the Membrane… Membrane Transport

2 categories

·   Passive transport (does not require energy)

·   Active transport (does require energy)

Passive transport

·   3 types

Diffusion

·   the movement of particles from high concentration to lower concentration

·   what is concentration?

·   kinetic energy (all molecules are in motion)

·   Brownian movement

·   When does it stop?

·   Rate of Diffusion

1.   

2.   

3.   

4.   

Osmosis

·   Solvent

·   Solute

·   Osmosis is when water diffuses across a selectively permeable membrane. (Water can pass but the solute cannot!)

·   During osmosis, water moves from an area where there is more water to an area where there is less water (water usually moves toward the higher concentration)

·   3 types of solutions

o hypotonic (outside is more dilute)

o hypertonic (inside is more dilute)       

o isotonic (equal concentrations)

·   osmotic swelling can cause cell to burst (lyse) or shrink so how do they deal?

a.   Cell walls

b.   Contractile vacuoles

c.   Pump ions out

d.   Blood is isotonic to cytosol

Facilitated diffusion

·   Helped across the cell (i.e. glucose)

·   Special protein channels (specific to the molecule it is transporting)

·   No energy

Active Transport

·   Requires energy!

·   Why do cells need active transport?

o Cells require substances that are at a lower concentration outside of the cell

·   Special proteins transport these substances

Endocytosis

·   Used for macromolecules (too big to pass thru)

·   CM bends inwards, forms vesicle with extracellular fluid and substance

·   Vesicle fuses with lysosome

·   Phagocytosis

·   Pinocytosis

·   Exocytosis