Membrane Different membranes –All have similar functions & structures –Plasma membrane separates inside of cell from outside of cell –Other membrane define organelles to form compartments of eukaryotic cells Forms a selectively permeable layer –Lets some things in or out but not all –Like a window screen

Membrane Phospholipid bilayer –Phosphate group facing outward hydrophillic –Fatty acid tails face each other hydrophobic Proteins also in membrane –Lots of functions Signaling Transport Enzymatic –Peripheral- on inside or outside surface –Integral- proteins stick out on both sides

Permeability in membranes Selectively permeable –Some move easily through the lipid layer Non polar molecules (O 2, alcohols) Small polar molecules (H 2 O, CO 2 ) Move with (or down) a concentration gradient –From areas of high to low concentration –Some need help to get through Like ions and larger polar molecules (sugar, a.a.) Transport proteins assist –Channel proteins - allow passage of charged particles –Carrier proteins- transport specific molecules

Diffusion Defined as passive movement of moleculesdown a concentration gradient from areas of high to low conc. This does not require energy - (passive) Eventually the molecules will be equally distributed (equillibrium is reached)

Osmosis Movement of water molecules from high to low concentration across a semi-permeable membrane Or diffusion of water HypotonicHypotonic solution outside cell –Low solute concentration –High water concentration –Water moves into cell HypertonicHypertonic solution outside cell –High solute concentration –Low water concentration –Water leaves cell IsotonicIsotonic solution –Concentration of water equal on both sides of membrane –No change in concentration will occur

Water in Plants Plant cells normally in hypotonic environment –Central vacuole full –Puts pressure on cell wall –Cell doesn’t burst because of cell wall Plants in hypertonic solution –Lose water and usually kills cell

Passive transport Involves movement of molecules across a membrane From areas of high concentration to areas of lower concentration across a membrane –Spilled perfume example Without energy

Facilitated transport Like passive transport but requires a membrane protein to help (facilitate) the movement Does not require energy Moves with concentration gradient

Active Transport Moves molecules across a membrane –Via a membrane protein –Can move molecules against their concentration gradient From low to high concentration Not easy to put spilled perfume back into bottle –Requires energy (ATP)

Exo or endocytosis Exocytosis- molecules exiting cell –Ex. Transport vesicle releasing contents outside cell Endocytosis- molecules entering cell –Phagocytosis - cell eating Ex. White blood cell eating bacteria –Pinocytosis - cell drinking –Receptor mediated endocytosis Molecule binds to protein receptor Ex. Cholesterol in liver cells

Cell signaling Signal transduction pathway –How cells talk to each other –Reception Outside molecule binds to receptor Ex. Adrenaline to muscle cells –Transduction Message relayed inside cell via chemicals –Response Chemical action Ex. Breakdown glycogen to release glucose