Chapter 5Chapter 5

The Plasma MembraneThe Plasma Membrane

The Cell Membrane:The Cell Membrane:

OUTSIDE

INSIDE

HYDROPHILIC HEAD

HYDROPHOBIC TAIL

TRANSPORT PROTEIN

The cell membrane is referred to as a PHOSPHOLIPID

BILAYER

The Plasma MembraneThe Plasma Membrane

It contains two layers of phospholipidsIt contains two layers of phospholipids The hydrophobic (water-hating) tails face The hydrophobic (water-hating) tails face

each other like peanut butter and jelly.each other like peanut butter and jelly. The hydrophilic heads face the watery The hydrophilic heads face the watery

exteriors of the bilayerexteriors of the bilayer Sometimes fats, proteins, and other Sometimes fats, proteins, and other

carbohydrate molecules float around the carbohydrate molecules float around the bilayer like ice cubes in water. They are bilayer like ice cubes in water. They are not stationarynot stationary..

A Gallery of Membrane A Gallery of Membrane ProteinsProteins

Passive transporters- channels that Passive transporters- channels that allow specific thing to enter the cell allow specific thing to enter the cell without inputting energy.without inputting energy.

Go to: Go to: http://www.sp.uconn.edu/~terry/images/anim/symport.gif

A Gallery of Membrane A Gallery of Membrane ProteinsProteins

Active Transporters- channels that Active Transporters- channels that allow specific thing to enter the cell allow specific thing to enter the cell with the input of energy (ATP)with the input of energy (ATP)

DiffusionDiffusion

Diffusion: The movement of Diffusion: The movement of molecules to an area of high molecules to an area of high concentration [concentration [] to an area of low ] to an area of low concentration [concentration [] until the ] until the concentration is the same concentration is the same everywhere.everywhere.

OsmosisOsmosis Water may constantly pass into and out Water may constantly pass into and out

of cells through these plasma of cells through these plasma membranes (lipid bilayers). This membranes (lipid bilayers). This uninterrupted flow of water through uninterrupted flow of water through these membranes is called these membranes is called OSMOSISOSMOSIS..

Water has the free pass to travel in and Water has the free pass to travel in and out of organisms and cells. So water is out of organisms and cells. So water is called a solvent.called a solvent.

Why do I “melt” when salt is poured on me?

Because water always goes to where there is more “stuff”

HypotonicHypotonic

Hypotonic- having a lower Hypotonic- having a lower concentration of solutesconcentration of solutes

HypertonicHypertonic

Hypertonic- having a higher Hypertonic- having a higher concentration of solutesconcentration of solutes

What about fish?What about fish?Do either of these fish need to “drink” the water

to survive? Who will it be?We drink the

water because there is more “stuff” in the

ocean than in us. Therefore, we must drink the

water to recover the water we

lose to osmosis.

Other Transport Other Transport MechanismsMechanisms

Membranes are selectively Membranes are selectively permeable permeable -- -(they only let -(they only let specific stuff pass to the specific stuff pass to the other other side)side)

Passive TransportPassive Transport

Substances move DOWN their Substances move DOWN their concentration gradient into or out of concentration gradient into or out of the cell (a person going down a the cell (a person going down a water slide) water slide)

No extra energy is required to No extra energy is required to perform passive transport.perform passive transport.

Active TransportActive Transport

Substances move through transport Substances move through transport proteins but AGAINST the proteins but AGAINST the concentration gradient. Cells use concentration gradient. Cells use free energy (usually from ATP) to do free energy (usually from ATP) to do this. It requires extra energy. this. It requires extra energy.