Cell MembraneCell Membrane

Structure & FunctionStructure & Function

Biology 11Biology 11

Ms. LowrieMs. Lowrie

HomeostasisHomeostasis

Definition:Definition:– Constant state or balance within our Constant state or balance within our

internal environment even when the internal environment even when the external environment changesexternal environment changes

Required by each cell to continue lifeRequired by each cell to continue life

Maintained by cell membraneMaintained by cell membrane

Cell MembraneCell Membrane

Selectively permeableSelectively permeable– Allows some molecules to pass Allows some molecules to pass

through while stopping othersthrough while stopping others– a.k.a. semi-permeablea.k.a. semi-permeable

PermeabilityPermeability– Degree to which substances can Degree to which substances can

passpass

Parts of the Parts of the Cell Cell MembraneMembrane

extracellular fluid (outside cell)

cytoplasm (inside cell)

microfilamentsperipheral

protein

integral protein

cholesterol

glycolipid glycoprotein

carbohydrate chain

headtails

phospholipid bilayer

Fluid Mosaic ModelFluid Mosaic Model

FluidFluid– Phospholipids not Phospholipids not

attached & are attached & are able to moveable to move

MosaicMosaic Mixture, varietyMixture, variety

– Made of many Made of many partsparts

– Proteins floating Proteins floating throughout itthroughout it

Fluid Mosaic ModelFluid Mosaic Model

Phospholipid BilayerPhospholipid Bilayer

Two layer membrane Two layer membrane Phospholipids are NOT attached Phospholipids are NOT attached

togethertogether– FlexibleFlexible– Small holes willSmall holes will

seal quicklyseal quickly

PhospholipidsPhospholipids

Heads point outward Heads point outward – HydrophilicHydrophilic

Water attracting/lovingWater attracting/loving

Tails point inwardTails point inward– HydrophobicHydrophobic

Water repelling/Water repelling/

fearing fearing

Why are cells round?Why are cells round?

Because they are Because they are surrounded by surrounded by fluid...fluid...

Carbohydrate ChainCarbohydrate Chain

Chain of sugar moleculesChain of sugar molecules

Gives identity (unique marking)Gives identity (unique marking) for each type of cellfor each type of cell– Similar to a “fingerprint”Similar to a “fingerprint”

May be attached to a May be attached to a protein or a lipidprotein or a lipid

Cell IdentityCell Identity

DonationDonation– BloodBlood– OrgansOrgans

Immune Immune systemsystem

extracellular fluid (outside cell)

cytoplasm (inside cell)

glycolipid glycoprotein

carbohydrate chain

GlycoproteinGlycoprotein

Protein on outside of membrane Protein on outside of membrane – With carbohydrate chain attachedWith carbohydrate chain attached

Gives identityGives identity

glycoprotein

GlycolipidGlycolipid

Phospholipid on outside of Phospholipid on outside of membrane membrane – With carbohydrate chain attachedWith carbohydrate chain attached

Gives identityGives identity

Integral ProteinIntegral Protein

Protein extending through bilayerProtein extending through bilayer Contains channels Contains channels Moves molecules in/outMoves molecules in/out

a.k.a:a.k.a:– Carrier …Carrier …– Channel … Channel … – Gatekeeper …Gatekeeper …– Transport …Transport …– Membrane …Membrane …

Peripheral ProteinPeripheral Protein

Protein on inside layer of Protein on inside layer of membranemembrane

Attaches to microfilaments for Attaches to microfilaments for supportsupport

CholesterolCholesterol

Embedded in membraneEmbedded in membrane Allows membrane to function Allows membrane to function

in all temperaturesin all temperatures

Not all cholesterol is Not all cholesterol is bad!bad! In high temperaturesIn high temperatures

– Keeps membrane rigidKeeps membrane rigid

In low temperatures In low temperatures – Keeps membrane flexibleKeeps membrane flexible– Prevents cells from freezingPrevents cells from freezing

MicrofilamentsMicrofilaments

– a.k.a. “filaments of cytoskeleton”a.k.a. “filaments of cytoskeleton” Provides support for membraneProvides support for membrane

Other PartsOther Parts

Extracellular fluidExtracellular fluid– Fluid outside cellFluid outside cell

CytoplasmCytoplasm– Fluid inside cellFluid inside cell

What do you see?What do you see?

QuestionsQuestions

Answer:Answer:– #1, 2 & 5 (pg 49)#1, 2 & 5 (pg 49)

Hints:Hints:#1#1

““molecular structure” means what it is molecular structure” means what it is made ofmade of

#5#5 Look for 3 functions in the textLook for 3 functions in the text

#1 – Molecular #1 – Molecular StructureStructure Phospholipid bilayer

– Hydrophilic heads facing out– Hydrophobic tails facing in

Embedded with:– Proteins (peripheral & integral)– Glycoproteins– Glycolipids– Cholesterol

#2 – Fluid Mosaic #2 – Fluid Mosaic ModelModel Fluid:

– Phospholipids that are not attached to each other

Can easily move around and reposition

– Flexible Mosaic:

– Embedded with proteins mixed throughout

#5 – Protein Functions#5 – Protein Functions

1. Allow materials to move into and out of cell (integral)

2. Cell recognition/identity (glycoprotein)

3. Support (peripheral)4. Receptor sites for hormones

Extra QuestionsExtra Questions

A.A. Why is it important for the cell Why is it important for the cell membrane to be fluid?membrane to be fluid?

B.B. Define: selectively permeable, Define: selectively permeable, impermeable, permeable. Which term impermeable, permeable. Which term applies to the cell membrane? Why?applies to the cell membrane? Why?

C.C. Why do cells need an ‘identity’?Why do cells need an ‘identity’?

D.D. Why is cholesterol important?Why is cholesterol important?

E.E. List 3 materials that move into or out of List 3 materials that move into or out of cells.cells.

F.F. Contrast a cell membrane & cell wall.Contrast a cell membrane & cell wall.

A – Fluid MembraneA – Fluid Membrane

Allows for some movement without damage

Phospholipids rejoin quickly if a small hole is made

B – PermeabilityB – Permeability

Selectively/Semi – some things are allowed in or out

Impermeable – nothing … Permeable – everything …

Cell membrane = selectively permeable– Protects the cells

C – Cell C – Cell IdentityIdentity Blood donationBlood donation Organ Organ

transplanttransplant Immune Immune

systemsystem– Detects invaders Detects invaders

Allows cells to Allows cells to function in all function in all temperaturestemperatures

High temperatures:High temperatures:– Keeps membrane rigidKeeps membrane rigid

Low temperatures: Low temperatures: – Keeps membrane Keeps membrane

flexibleflexible– Prevents cells from Prevents cells from

freezingfreezing

D – D – CholesterolCholesterol

E – What Moves?E – What Moves?

In:In: WaterWater OxygenOxygen Carbon dioxideCarbon dioxide Glucose (sugar)Glucose (sugar) MineralsMinerals NutrientsNutrients

Out:Out: WaterWater OxygenOxygen Carbon DioxideCarbon Dioxide WastesWastes

F – Membrane vs. WallF – Membrane vs. Wall

Cell Membrane Living Made of proteins &

phospholipids Materials pass

between phospholipids

Found in plant and animal cells

Cell Wall Nonliving Made of

cellulose Materials pass

through small pores

Found in plant cells only

Any QuestionsAny Questions