Plasma Membrane:Plasma Membrane:The Gate KeeperThe Gate Keeper

Ms. PolsonMs. Polson

BiologyBiology

October October 18,200918,2009

Plasma MembranePlasma MembraneLesson ObjectivesLesson Objectives

Students will be able to:Students will be able to:

Use vocabulary related to transport across the plasma Use vocabulary related to transport across the plasma membranemembrane

Differentiate between active and passive transportDifferentiate between active and passive transport

Identify membrane structures that permit transportIdentify membrane structures that permit transport

Understand the function of the plasma membrane as a Understand the function of the plasma membrane as a “gate keeper”“gate keeper”

What is a Plasma What is a Plasma Membrane?Membrane? All living cells have themAll living cells have them

Selective permeabilitySelective permeability

AsymmetricAsymmetric

Gives cell structureGives cell structure

Cell-cell recognitionCell-cell recognition

Fluid mosaic modelFluid mosaic model– Lipid movement in bilayerLipid movement in bilayer

Maintains homeostasisMaintains homeostasis

Animal and PlantAnimal and PlantPlasma (cell) Membrane Plasma (cell) Membrane

Plasma MembranePlasma MembraneFunctionFunction

Separate inside organelles from external Separate inside organelles from external environmentenvironment

Regulate entrance and exit of substancesRegulate entrance and exit of substances Transfer informationTransfer information Establishment of electric potential differenceEstablishment of electric potential difference Site of biological activitiesSite of biological activities Attachment between cellsAttachment between cells Removal of wasteRemoval of waste

Plasma MembranePlasma MembranePhotograph: Cell MembranePhotograph: Cell Membrane

Plasma MembranePlasma MembraneStructureStructure

LipidsLipids– Phosphlipids, Glycolipids, SteroidsPhosphlipids, Glycolipids, Steroids– Hydrophilic and hydrophobic propertiesHydrophilic and hydrophobic properties– Gives flexibilityGives flexibility

ProteinsProteins– Integral - transport channelsIntegral - transport channels– Peripheral - recognition sitesPeripheral - recognition sites– Determines membranes specific functionsDetermines membranes specific functions

SugarsSugars

Lipid Bilayer ModelLipid Bilayer ModelCross SectionCross Section

Gorter and Grendel, Gorter and Grendel, 19251925

Two sheets of lipidsTwo sheets of lipids– 7.5 nm thick7.5 nm thick

Found around cellFound around cell

Embedded with Embedded with proteinsproteins

Strengthened with Strengthened with cholesterol cholesterol molecules (animal)molecules (animal)

Lipid Bilayer ModelLipid Bilayer ModelPhospholipid Phospholipid

HydrophilicHydrophilic– Water lovingWater loving– Phosphate endPhosphate end– Outside and inside Outside and inside

HydrophobicHydrophobic– Water fearingWater fearing– Lipid tail regionLipid tail region– CenterCenter

Plasma MembranePlasma MembraneHydrophilic and HydrophobicHydrophilic and Hydrophobic

Passive TransportPassive TransportSimple DiffusionSimple Diffusion

Result of inherent Result of inherent kinetic energykinetic energy– Thermal motion or Thermal motion or

heatheat

No energy neededNo energy needed

Diffusion and osmosisDiffusion and osmosis

High concentration to High concentration to low concentration: low concentration: small molecules small molecules – OO2 2 , CO, CO22, H, H22OO

Simple DiffusionSimple Diffusion

Passive TransportPassive TransportFacilitatedFacilitated DiffusionDiffusion

Proteins act as tunnelsProteins act as tunnels

Carrier proteins help Carrier proteins help larger polar molecules larger polar molecules cross membranecross membrane– GlucoseGlucose

Moves materials along Moves materials along concentration concentration gradientgradient

Active TransportActive Transport

Energy Energy isis needed needed

Low concentration to Low concentration to high concentrationhigh concentration

Movement of molecules Movement of molecules up concentration up concentration gradient gradient

Sodium-potassium Sodium-potassium pumppump

Active TransportActive Transport

Movement of large substances by vesiclesMovement of large substances by vesicles

– Endocytosis – taking into cellEndocytosis – taking into cell PhagocytosisPhagocytosis PinocytosisPinocytosis Receptor mediateReceptor mediate

– Exocytosis – expelling from cellExocytosis – expelling from cell ER or Golgi ApparatusER or Golgi Apparatus

Types of SolutionsTypes of Solutions

IsotonicIsotonic– Concentration of dissolved substances are the Concentration of dissolved substances are the

same inside and outside the cellsame inside and outside the cell

HypotonicHypotonic– Concentration of dissolved substances are lower Concentration of dissolved substances are lower

outside than insideoutside than inside

HypertonicHypertonic– Concentration of dissolved substances are higher Concentration of dissolved substances are higher

outside than insideoutside than inside

HomeostasisHomeostasisPlasma MembranePlasma Membrane

Maintains constant internal environmentMaintains constant internal environment

Controls movement of materials in and out of Controls movement of materials in and out of the cell as a “gate keeper”the cell as a “gate keeper”– Dynamic equilibriumDynamic equilibrium

Separates cellular organelles from external Separates cellular organelles from external environment environment

Vocabulary ReviewVocabulary Review

Plasma MembranePlasma Membrane HomeostasisHomeostasis Passive TransportPassive Transport Simple DiffusionSimple Diffusion Facilitated DiffusionFacilitated Diffusion Active TransportActive Transport HydrophilicHydrophilic

HydrophobicHydrophobic EndocytosisEndocytosis ExocytosisExocytosis IsotonicIsotonic HypertonicHypertonic HypotonicHypotonic

Questions…Questions…

Comments…Comments…

Thoughts?Thoughts?