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 (O2, alcohols)

• Small polar molecules (H2O, CO2)

• 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 molecules down 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• Hypotonic Hypotonic 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