UNIT#4:Cells

PARTTWO:Membrane&Transport

Whatisthecellmembrane?Wheredowefindit?

•  EVERYcellhasanouterlayerholdingthecelltogethercalledtheplasmamembrane.

Plasmamembrane

Cellwall

Plasmamembrane

Nucleus

CHEEKCELLS POTATOCELLS

Whatisthejoboftheplasmamembrane?

Weo3enrefertotheplasmamembraneasaGATEKEEPERbecauseitsjobsareto:

1.   Regulatewhatentersand

leavesthecell2.  ProvideprotecQonand

supporttothecell

Whatisaplasmamembranemadeof?

EXTRACELLULARFLUID

INTRACELLULARFLUID

POLAR

&

HYDROPHILIC

NONPOLAR

&

HYDROPHOBIC

1.ThePhospholipidMolecule

Whendothephospholipidsformamicelleasopposedtoaliposome?

2.TheCholesterolMolecule

Howwouldcholesterolbeplacedintheplasmamembrane?Why?

NONPOLAR

POLAR

3.ProteinMolecules

Proteinscanbeintegral(embedded)orperipheral(surface).

4.CarbohydrateChains(GlycoproteinandGlycolipid)

1.   Cell-tocell-recogniQon:surface“nametags”thatallowcellstorecognizeeachother(goodorbad).

2.  ImportantinsorOngcellsintoOssues&organsduringembryonicdevelopment

3.  BasisofrejecQonforforeigncellsbyimmunesystem

•  Glycolipid:carbohydratechainaSachedtoalipid•  Glycoprotein:carbohydratechainaSachedtoaprotein

MembraneFluidity–“TheFluidMosaicModel”

•  Fluidityistemperaturedependent.•  Astemperaturedecreases,themembranebecomesmorerigid.

•  Unsaturatedphospholipidsstayfluidlonger–bentduetodoublebondbetweencarbonatoms.

•  Saturatedphospholipidsaremorecloselypacked.

Whattypesofmoleculescancrosstheplasmamembranewithoutanyhelp?

TypesofIonsandMoleculesinsideaCell

TheplasmamembraneisselecQvely(semi-)permeable.Notall

substancescanpassthrough.

IONS:SmallandVeryPolar

UREA:Smallandpolar

GLUCOSE:LargeandPolar

CO2:SmallandNonpolar

polar polar

small small

PRACTICE:Whichmoleculeswouldbeableto

crossthecellmembranefreelywithoutthehelp

ofamembraneprotein?

DIFFUSIONisnetmovementofmoleculesorionsdowntheir

ownconcentraQongradient.

•  Forexample:O2andCO2

Osmosis is the diffusion of WATER across a selectively permeable membrane.

What is the net movement of water in the beaker: LEFT or RIGHT?

The Effects of Osmosis on Animal Cells Hypotonic:

the solution has a LOWER solute concentration than inside the cell

�below strength�

Isotonic:

the solution has the SAME solute concentration as inside the cell

�same strength�

Hypertonic:

the solution has a HIGHER solute concentration than inside the cell

�above strength�

The Effects of Osmosis on Plant Cells In a HYPOTONIC

solution: In an ISOTONIC

solution: In a HYPTERTONIC

solution:

WATCH THIS: http://www.youtube.com/watch?v=VK-_YHakvho&feature=related

Water leaves the central vacuole and the cell membrane peals away from the cell wall

Howdoothermaterialscrosstheplasmamembranedown

theirconcentraQongradient?

•  Ifamaterialistoolarge,polar,orcarriesacharge,thenitneedstopassthroughamembrane-spanningprotein.

•  Ifdiffusionoccursthroughamembrane-spanningprotein,thenitiscalledFACILITATEDDIFFUSION.

Someproteinchannelsusedinfacilitateddiffusionareopenallthe

Qme,whileotherproteinchannelsaregated.

•  Somegatedproteinchannelsareopenedbya“key”likeahormonemolecule.

Hormone-controlledGatedProteinChannel VoltageGatedProteinChannel

•  Othergatedproteinchannelsareopenedbyachangeinvoltage(charge)acrossthemembrane.

ThreeTypesofPassiveTransport

WiththeconcentraOongradientanddoesNOTuseenergytomovesubstances

TypesofAcQveTransportAgainsttheconcentraOongradientandUsesenergytomovesubstances

TheSodium-PotassiumPump

TYPESOFENDOCYTOSIS:processofengulfingmaterialsINTOacell

Parameciumbeingeatenbyanamoebathroughendocytosis

EXOCYTOSIS:vesiclesfusingwithcellmembranetopush

materialsOUTofthecell.

Review of Cell Transport

TheEffectofConcentraQonDifferenceontheRateofTransport

inDifferentTypesofTransport

Creates a hypotonic environment for the brain cells. Water will diffuse into the brain cells via osmosis. Without a cell wall to protect them from intracellular water pressure, the brain cells will lyse.

Paramecium would continuously take in water via osmosis when immersed constantly in a hypotonic solution. Paramecium do not have cell walls to protect them again lysis, so the contractile vacuole is necessary to rid the Paramecium of the excess water.