Cell Transport• Moving things into and out of the cell

through the cell membrane to maintain balance (homeostasis)

• Passive:– Doesn’t take any energy from the cell– Just happens (kinetic energy of

molecules)

• Active:– Uses the cell’s energy– ATP (Adenosine TriPhosphate)

Cell Memebrane• Phospholipid Bilayer

– 2 layers, back to back, of molecules of fat called phospholipids

• Fluid Mosaic– Other molecules, too, like proteins, but

they don’t just sit there, they move around

• Selectively permeable– Not just anything can pass through

Cell membrane

Diffusion• Molecules simply move from an

area of higher concentration to lower (with concentration gradient)

• Because of the molecules’ kinetic energy (passive)

• Will stop when reach equilibrium (equal concentration)

• Molecules still move, but for each one that moves in to the cell, one moves out (no net movement)

Diffusion across cell membrane

• Happens only for very small particles (salt, etc.)

• Move between phospholipid molecules of the bilayer

• Or for molecules that are nonpolar (hydrophobic) and dissolve into the

space between the two layers of the cell membrane, but not in water

Facilitated diffusion• For molecules that are too big to get

in (e.g. sugar), or have charges (ions)

• Proteins in the cell membrane will chemically bind to the molecule. (specific…only 1 molecule per protein…like a lock and key)

• The protein will then change shape and the molecule will move in or out of the cell.

• Takes no energy (passive)

Facilitated diffusion

•Note: each protein is specific for one molecule, but there are many different proteins in each cell membrane

Osmosis• Special kind of diffusion (passive)• Only for water across the

membrane• Water can move against its

concentration gradient, that is water can move from low water

to high water concentration• Water moves to “water down”

whatever is most concentrated.

Osmosis• If the cell has more “stuff”

dissolved outside than inside, it is in a hypertonic

environment• It will try to “water down” the

environment to make it less harsh

• Water leaves the cell, the cell shrinks (plasmolysis)

• http://www.youtube.com/watch?v=gWkcFU-hHUk&feature=related

Osmosis• If the cell has more “stuff” dissolved

inside than outside, it is in a hypotonic environment

• It will try to “water down” the inside to make it less harsh

• Water enters the cell, the cell grows • If it gets too big, it explodes (cytolysis)• http://vimeo.com/2726364

Osmosis• If the cell has equal amounts of

“stuff” dissolved inside and out, it is in an isotonic environment

• Water molecules will move both in and out of the cell equally, so there is no net movement of water

• Notes: water still moves in and out in hypertonic and hypotonic

solutions, but the net movement is in one direction

Equilibrium• Passive transport will continue

until equal concentrations are reached in and out of the cell (equilibrium).

• Molecules still move back and forth across the membrane, but do so at equal rates

• No net (total) movement of molecules, though

Active Transport• Sometimes cell wants higher or

lower concentrations (not equilibrium)

• Have to use the cell’s energy (ATP adenosine triphosphate)

• Moves against concentration, i.e. from low to high concentration

• Moves large molecules or large amounts of molecules

Protein Pumps• Energy changes shape of the

protein to move things in/out of the cell

• Is specific…each protein can only chemically bind with one

molecule, but there are many different proteins in the cell membrane (like a lock and key)

• Na+ K + pump

Protein pumps

• 3 sodiums are taken out of the cell and 2 potassiums brought in using ATP.

Transport by vesicle• Moves large molecules or large

quantities of something into and out of the cell

• Into the cell is called endocytosis– Pinocytosis: water/liquid moves–Phagocytosis: solids move

• Out of the cell is called exocytosis (e.g. products from

Golgi Apparatus)

Endocytosis

•Note part of cell membrane makes the vesicle and is now inside the cell!

•http://www.youtube.com/watch?v=W6rnhiMxtKU

Exocytosis

•Note the vesicle fuses with the cell membrane and is now part of it!

•http://www.youtube.com/watch?v=U9pvm_4-bHg

ATP

•Adenosine Triphosphate

•ATP

•Adenosine Diphosphate

•ADP + P + energy