PLASMA MEMBRANEPLASMA MEMBRANE

Plasma Membrane

• Boundary that separates the living cellliving cell from it’s nonnon--livingliving surroundings.

•• Phospholipid bilayerPhospholipid bilayer•• AmphipathicAmphipathic - having both:

hydrophilic headshydrophobic tails

• ~8 nm thickPhospholipidPhospholipid

Plasma Membrane Plasma Membrane -- cont.cont.

•• Controls trafficControls traffic into and out of the cell with phospholipidsphospholipids and and transport proteinstransport proteins..

•• Selectively permeableSelectively permeable

Transport proteinTransport protein

Selective PermeabilitySelective Permeability

• The propertyproperty of biological membranesbiological membraneswhich allows some substances to cross more easily than others.

Fluid MosaicFluid Mosaic

• 1972 - SingerSinger and NicolsonNicolson called the membrane a “Fluid Mosaic Model”.

•• Mosaic:Mosaic: different proteins embedded in the phospholipids.

•• Fluid:Fluid: proteins and phospholipids can move freely in the membrane.

Fluid Mosaic Fluid Mosaic -- cont.cont.

• Components of a phospholipid bilayer.1.1. phospholipidsphospholipids2.2. proteins proteins -- enzymes, receptors, transport.enzymes, receptors, transport.3.3. glycolipidsglycolipids4.4. glycoproteinsglycoproteins5.5. carbohydratescarbohydrates6.6. cholesterolcholesterol

Transport ProteinsTransport Proteins

•• TransportsTransports moleculesmolecules or ionsions across biological membranes

•• 3 types of transport proteins3 types of transport proteins:11. uniportuniport

22. symportsymport

33. antiportantiport

Uniport Transport ProteinUniport Transport Protein

• Carries a single solutesingle solute across the membrane.

extracellularfluid

intracellularfluid

Symport Transport ProteinSymport Transport Protein

•• Translocate 2 different solutesTranslocate 2 different solutes simultaneously in same direction.

intracellularfluid

extracellularfluid

Antiport Transport ProteinAntiport Transport Protein

•• Exchanges 2 solutesExchanges 2 solutes by transporting them in opposite directionsopposite directions.

intracellularfluid

extracellularfluid

DiffusionDiffusion

• The net movement of a substance (molecules)down a concentrationconcentration gradientgradient from an area of highhigh concentrationconcentration to an area of lowlowconcentrationconcentration.

•• passive transport:passive transport: NONO energyenergy is expended.

•• facilitated diffusion: facilitated diffusion: type of passive transportpassive transportwhich uses transport proteins.transport proteins.

OsmosisOsmosis

• The movement of waterwater across selectively selectively permeable membranespermeable membranes.

• The waterwater moves from a high concentrationhigh concentrationto low concentrationlow concentration.

Question:Question:WhatWhat’’s in a Solution?s in a Solution?

Answer:Answer:

•• solutesolute + solventsolvent → solutionsolution

•• NaClNaCl + HH2200 → saltwatersaltwater

HypertonicHypertonic

• A solutionsolution with a greater solutegreater soluteconcentrationconcentration compared to another solutionsolution.

3% NaCl97% H2O

Red Blood Cell

5% NaCl95% H2O

solutionsolution

HypotonicHypotonic

• A solutionsolution with a lower solute concentrationlower solute concentrationcompared to another solutionsolution.

3% Na97% H2O

Red Blood Cell

1% Na99% H2O

solutionsolution

IsotonicIsotonic

• A solutionsolution with an equal solute concentrationequal solute concentrationcompared to another solutionsolution.

3% Na97% H2O

Red Blood Cell

3% Na97% H2O

solutionsolution

Movement of HMovement of H22OO

• Water will ““ALWAYSALWAYS”” diffuses down a concentration gradient from a HYPOTONICHYPOTONICsolutionsolution to a HYPERTONICHYPERTONIC solutionsolution.

““ALWAYS REMEMBERALWAYS REMEMBER””•• HYPOTONICHYPOTONIC →→ HYPERTONICHYPERTONIC

Animal CellsAnimal Cells•• Animal cellsAnimal cells placed into a hypotonic solution

will HEMOLYSIS (EXPLODE).HEMOLYSIS (EXPLODE).•• Animal cellsAnimal cells placed into a hypertonic solutionhypertonic solution

will CRENATE (SHRIVEL).CRENATE (SHRIVEL).

HemolysisCrenation

RedRedBloodBloodCellsCells

Plant CellsPlant Cells• Firmness or tension (vacuole full)(vacuole full) that is found

in plant cells (cell wall) that are in a hypotonic environment is called TURGIDTURGID..

• This process is called TURGOR PRESSURE.TURGOR PRESSURE.

WaterWater

CellWall Water

CentralVacuole

Plant CellsPlant Cells• When the plasma membraneplasma membrane pulls away from

the cell wallcell wall (vacuole empty)(vacuole empty) in a hypertonic hypertonic environmentenvironment (loss of water)(loss of water) is called PLASMOLYSISPLASMOLYSIS.

Water Water

CellWall Water

plasma membraneplasma membrane

Active TransportActive Transport

• The movement of moleculesmovement of molecules (small or large) across the plasma membraneplasma membrane in which energy energy (ATP)(ATP) is requiredrequired.

•• Examples:Examples:

1.1. Sodium (Na) Sodium (Na) -- Potassium (K) PumpPotassium (K) Pump2.2. ExocytosisExocytosis3.3. EndocytosisEndocytosis

Sodium-Potassium Pump

• The mechanism that uses energy (active transport)energy (active transport)released from splitting ATPsplitting ATP to transport Sodium Sodium (Na(Na++)) out out of and Potassium (KPotassium (K++) into cells. ) into cells.

extracellularfluid

intracellularfluid

Na+ Na+

K+ K+

Question:Question:

•• How are large molecules transported into How are large molecules transported into and out of the plasma membranes?and out of the plasma membranes?

Answer:Answer:

•• Exocytosis and EndocytosisExocytosis and Endocytosis

ExocytosisExocytosis

•• Cell Cell secretes macromoleculessecretes macromolecules (proteins and (proteins and other biochemicals) other biochemicals) outout of cell.of cell.

•• Part of the Endomembrane System:Part of the Endomembrane System: the fusion of transport vesicles with plasma membrane.

EndocytosisEndocytosis

• The energyenergy requiring movementmovement of particlesparticles(foreign or natural)(foreign or natural) intointo the cell.

•• 3 types of endocytosis:3 types of endocytosis:A.A. PhagocytosisPhagocytosisB.B. PinocytosisPinocytosisC.C. ReceptorReceptor--mediated endocytosismediated endocytosis

A. A. PhagocytosisPhagocytosis

•• Cell eating:Cell eating: cells engulf particles with pseudopodiapseudopodia and pinches off a food pinches off a food vacuolevacuole..

•• Two examples:Two examples:1.1. White Blood CellWhite Blood Cell2.2. AmoebaAmoeba

FoodFoodVacuoleVacuole White Blood Cell

Bacteria

B. PinocytosisB. Pinocytosis• Cell drinking: droplets of extracellular fluid

are absorbedabsorbed intointo the cell by small vesiclessmall vesicles.

•• Example:Example:1.1. FungiFungi

Food Particles

Hyphae

C. ReceptorC. Receptor--Mediated EndocytosisMediated Endocytosis

• Importing specific macromolecules (hormones)specific macromolecules (hormones)intointo the cell by the inward budding of vesiclesinward budding of vesiclesformed from coated pits (receptors).

Hormones

Receptors

Liver Cell