Cell MembraneCell Membrane

Controls What Enters or Exits the Controls What Enters or Exits the CellCell

Cell Membrane: OutlineCell Membrane: Outline• StructureStructure• FunctionFunction• How does structure fit the function?How does structure fit the function?• Passive transportPassive transport• Active transportActive transport

Cell Membrane: StructureCell Membrane: Structure

• Phospholipid bilayerPhospholipid bilayer

• CholesterolCholesterol • Integral proteinsIntegral proteins;; transport, transport,

identificationidentification

Structure: PhospholipidsStructure: Phospholipids

• Two layers of phospholipid molecules; Two layers of phospholipid molecules; ‘bilayer’‘bilayer’

• Similar to fats:Similar to fats:

– One fatty acid ‘tail’ is replaced with One fatty acid ‘tail’ is replaced with a phosphate group a phosphate group

– Phosphate groups are Phosphate groups are waterwater soluble soluble

GlycerolGlycerol: head

Fatty acidFatty acid ‘tails’

Structure: PhospholipidsStructure: Phospholipids• Selectively PermeableSelectively Permeable only allows certain only allows certain

substances to pass through easilysubstances to pass through easily

• HydrophilicHydrophilic = ‘ = ‘water loving’water loving’

• HydrophobicHydrophobic = ‘water fearing’= ‘water fearing’

‘heads’ = = HydrophilicHydrophilic: water soluble

‘tails’ = = Hydrophobic:Hydrophobic: water insoluble

CholesterolCholesterol helps to stabilize the membrane

Membrane structure

Cell Membrane: Selectively Cell Membrane: Selectively PermeablePermeable

• Passes easily:Passes easily:• SmallSmall

• Hydrophobic; nonpolar; lipid soluble Hydrophobic; nonpolar; lipid soluble (vitamins, alcohol)(vitamins, alcohol)

• Small hydrophilic; polar (water)Small hydrophilic; polar (water)

Cell Membrane: Selectively Cell Membrane: Selectively PermeablePermeable

• Difficult or impassableDifficult or impassable::

• Large polar (glucose) difficultLarge polar (glucose) difficult

• Ions; sodium (Na); calcium (Ca) difficultIons; sodium (Na); calcium (Ca) difficult

• Large substances impassableLarge substances impassable

Selectively PermeableSelectively Permeable

• Easy:Easy:• Lipid solubleLipid soluble

• Carbon dioxideCarbon dioxide

• OxygenOxygen

• Water Water

• Hard:Hard:• GlucoseGlucose

• IonsIons

• Large substancesLarge substances

Selectively PermeableSelectively Permeable

• How do large or charged molecules pass How do large or charged molecules pass through?through?

• SpecialSpecial TRANSPORT PROTEINSTRANSPORT PROTEINS are imbedded in the bilayerare imbedded in the bilayer

– ‘‘Tunnels’Tunnels’

Cell Membrane Cell Membrane Functions:Functions:

• Transport of substancesTransport of substances

• Cell-to-cell signalingCell-to-cell signaling

• Cell-to-cell communicatingCell-to-cell communicating

• Cell attachmentCell attachment

Fluid Mosaic ModelFluid Mosaic Model

• Many different kinds of proteins imbedded Many different kinds of proteins imbedded in the phospholipid bilayerin the phospholipid bilayer

• MosaicMosaic = picture made of many smaller = picture made of many smaller parts (proteins)parts (proteins)

• FluidFluid = moving, dynamic = moving, dynamic

Cell Membrane: FunctionCell Membrane: Function

1.1. Shape; Shape;

Shape can changeShape can change

Amoeboid movement

Cell Membrane: FunctionCell Membrane: Function

2.2. Regulate what enter/exits the cellRegulate what enter/exits the cell

Selectively permeableSelectively permeableHomeostasisHomeostasis = balance of = balance of

chemicals and temperature chemicals and temperature

needed to liveneeded to live

2 Types of Cellular Transport2 Types of Cellular Transport

• PassivePassive = kinetic energy of molecules in = kinetic energy of molecules in motion is enough to let molecules move motion is enough to let molecules move in/outin/out

• ActiveActive = cell has to expend energy to move = cell has to expend energy to move substancessubstances

How Materials Get InsideHow Materials Get Inside

• Passive TransportPassive Transport

• DiffusionDiffusion

• OsmosisOsmosis

• Facilitated diffusionFacilitated diffusion

• Active TransportActive Transport

• Sodium/potassium Sodium/potassium ‘pump’‘pump’

• EndocytosisEndocytosis

• Exocytosis Exocytosis

Passive TransportPassive Transport

1.1. DiffusionDiffusion2.2. OsmosisOsmosis

3.3. Facilitated diffusionFacilitated diffusion

Diffusion Diffusion • Kinetic energy – Kinetic energy – molecules in motionmolecules in motion

– As molecules bump into each other they As molecules bump into each other they get as far apart as they canget as far apart as they can

• Molecules move from an area of Molecules move from an area of highhigh concentration to an area of concentration to an area of lowlow concentrationconcentration

• ‘‘Spread out’Spread out’

Diffusion

Diffusion - TermsDiffusion - Terms• Concentration gradientConcentration gradient = when an area = when an area

has more molecules compared to another has more molecules compared to another areaarea

• EquilibriumEquilibrium = equal distribution of = equal distribution of molecules; no net change in movementmolecules; no net change in movement

DiffusionDiffusion

• Gases diffuse easilyGases diffuse easily

– Carbon dioxide, COCarbon dioxide, CO2, 2, Oxygen, OOxygen, O22

– Oxygen Oxygen diffuses from the lungs into diffuses from the lungs into RBC’sRBC’s

– Carbon dioxideCarbon dioxide diffuses from diffuses from RBC’s into lungsRBC’s into lungs

– GAS EXCHANGEGAS EXCHANGE

Passive TransportPassive Transport

1.1. DiffusionDiffusion

2.2. OsmosisOsmosis3.3. Facilitated diffusionFacilitated diffusion

• Diffusion of Diffusion of waterwater• Cells Cells AREARE a solution: a solution:

– Organelles, sugar, amino acids, salts Organelles, sugar, amino acids, salts dissolved in waterdissolved in water

• Cells are Cells are ININ a solution a solution• Compare the solution inside the cell to the Compare the solution inside the cell to the

solution outside the cellsolution outside the cell

OsmosisOsmosis

OsmosisOsmosis

• SolutionSolution:: two or more substances mixed two or more substances mixed togethertogether

– SoluteSolute – part being dissolved (ex. Sugar) – part being dissolved (ex. Sugar)

– SolventSolvent – part doing the dissolving – part doing the dissolving (water)(water)

OsmosisOsmosis

• Describe solution as a concentrationDescribe solution as a concentration

– How much solute dissolved in solventHow much solute dissolved in solvent

• Ex. 1%; 3%, 10% = Ex. 1%; 3%, 10% =

• 1% - solute; 99% 1% - solute; 99% waterwater

• 3%3% solutesolute; ; 97%97% water water

• 10% solute; 90% 10% solute; 90% waterwater

OsmosisOsmosis

• Compare solutions:Compare solutions:

–HypertonicHypertonic = solution with higher = solution with higher concentration of solutes than the concentration of solutes than the other solutionother solution

–HypotonicHypotonic = solution with low = solution with low concentration compared to the otherconcentration compared to the other

OsmosisOsmosis

• IsotonicIsotonic = when the two solutions are = when the two solutions are EQUAL in concentrationEQUAL in concentration

•EquilibriumEquilibrium

Osmosis

1%

1%

Isotonic

1%

1% 3%

1%Isotonic

HypertonicHypertonic

3% - solutes 97%- water

1%-solutes 99% water

1%

1%

3%

1%

1%

3%

Isotonic

HypertonicHypertonic

HypotonicHypotonic

3% - solute 97% -water

1% -solute 99% water

1%

1%

3%

1%

0%

1%

Isotonic

HypertonicHypertonic

Hypotonic Hypotonic

Plasmolysis

Isotonic solution:Isotonic solution:

Hypertonic solution

Hypotonic solution Hypotonic solution

Turgor pressure: Turgor pressure: osmotic pressure osmotic pressure placed on plant placed on plant

cell walls cell walls

Contractile vacuole

Passive TransportPassive Transport

1.1. DiffusionDiffusion

2.2. OsmosisOsmosis

3.3. Facilitated diffusionFacilitated diffusion

Facilitated DiffusionFacilitated Diffusion

• Diffusion that requires a ‘helper’Diffusion that requires a ‘helper’

– Protein – specific 3d shapeProtein – specific 3d shape• Molecules would diffuse normally but due Molecules would diffuse normally but due

to large size, too slowlyto large size, too slowly

– GlucoseGlucose

– InsulinInsulin

Active TransportActive Transport

Cell Uses Energy To Move Cell Uses Energy To Move Substances Across The Substances Across The

MembraneMembrane

Active TransportActive Transport

• Sodium – Potassium Ion ‘Pump’Sodium – Potassium Ion ‘Pump’

• EndocytosisEndocytosis

• ExocytosisExocytosis

Sodium-potassium “Pump”Sodium-potassium “Pump”

• Cell needs to create a concentration Cell needs to create a concentration gradientgradient

• ‘‘Pumps’ sodium out and potassium insidePumps’ sodium out and potassium inside• Creates electrochemical gradientCreates electrochemical gradient• More + on the outside; nerve cellsMore + on the outside; nerve cells

Sodium/potassium pump

Endocytosis Endocytosis

• Endo – ‘into’Endo – ‘into’• Large particles; bacteria, foodLarge particles; bacteria, food• PhagocytosisPhagocytosis = ‘eating’; engulf ‘food’, = ‘eating’; engulf ‘food’,

bacteriabacteria• PinocytosisPinocytosis = ‘drinking’, water = ‘drinking’, water• Receptor-mediatedReceptor-mediated = specific = specific

Endocytosis

Phagocytosis

Phagocytosis

Exocytosis Exocytosis

• ExcretionExcretion = wastes; ammonia, = wastes; ammonia,

• SecretionSecretion = substance other cells need; = substance other cells need; insulin, enzymes, hormonesinsulin, enzymes, hormones

Exocytosis