PowerLecture:PowerLecture:Chapter 5Chapter 5

A Closer Look at Cell A Closer Look at Cell MembranesMembranes

CFTR is a protein channel for chloride ionsCFTR is a protein channel for chloride ions CFTR is a type of ABC transporter in all CFTR is a type of ABC transporter in all

prokaryotic and eukaryotic cellsprokaryotic and eukaryotic cells

Impacts, Issues: One Bad Impacts, Issues: One Bad Transporter and Cystic FibrosisTransporter and Cystic Fibrosis

Fig. 5.2, p.75

ATP ATP

Cystic fibrosis, the most common fatal Cystic fibrosis, the most common fatal genetic disorder in the U.S., results from a genetic disorder in the U.S., results from a mutation in CFTR genemutation in CFTR gene

Impacts, Issues: One Bad Impacts, Issues: One Bad Transporter and Cystic FibrosisTransporter and Cystic Fibrosis

Section 5.1: Section 5.1: Lipid BilayerLipid Bilayer

Basic frameworkBasic framework

Selectively permeableSelectively permeable

Two layers of Two layers of

phospholipidsphospholipids Hydrophilic headsHydrophilic heads Hydrophobic tailsHydrophobic tails

http://www.bioteach.ubc.ca/Bio-industry/Inex/graphics/lipidbilayer.gif

Every cell membrane has a mixed Every cell membrane has a mixed composition of phospholipids, glycolipids, composition of phospholipids, glycolipids, sterols, and proteinssterols, and proteins

Most phospholipids and some proteins can Most phospholipids and some proteins can

drift through membranedrift through membrane

Fluid Mosaic ModelFluid Mosaic Model

Overview of Overview of Membrane ProteinsMembrane Proteins

ReceptorProteins

RecognitionProteins

PassiveTransporters

ActiveTransporters

Fig. 5.6, p.79

Overview of Overview of Membrane ProteinsMembrane Proteins

AdhesionProteins

CommunicationProteins

Fig. 5.6, p.78

Span the lipid bilayerSpan the lipid bilayer PassivePassive

Ion selective (nerve and muscle cells)Ion selective (nerve and muscle cells) Change shape when they interact with soluteChange shape when they interact with solute

• GluT1 (glucose transporter) GluT1 (glucose transporter) Cotransporter Cotransporter

Active Active Pump solute (calcium pump, ATPase)Pump solute (calcium pump, ATPase)

Transport ProteinsTransport Proteins

Other ProteinsOther Proteins

Receptor -- Bind an extracellular substance Receptor -- Bind an extracellular substance that triggers changes in cell activitythat triggers changes in cell activity AntibodyAntibody

Recognition – ID tags for speciesRecognition – ID tags for species HLAs for tissue defenseHLAs for tissue defense

Adhesion – one cell bind to anotherAdhesion – one cell bind to another collagencollagen

Communication – channel between 2 cellsCommunication – channel between 2 cells Cardiac gap junctionCardiac gap junction

Section 5.3:Section 5.3:Concentration Gradient Concentration Gradient

Different in #/unit Different in #/unit volume of a volume of a substances substances between 2 regionsbetween 2 regions

Will move down Will move down “down” gradient“down” gradient

DiffusionDiffusion Movement of like Movement of like

molecules or ions molecules or ions down a gradientdown a gradient

Molecules move Molecules move on their own on their own gradientgradient

Factors Affecting Factors Affecting Diffusion RateDiffusion Rate

Steepness of concentration gradientSteepness of concentration gradient Steeper gradient, faster diffusionSteeper gradient, faster diffusion

Molecular sizeMolecular size Smaller molecules, faster diffusionSmaller molecules, faster diffusion

TemperatureTemperature Higher temperature, faster diffusionHigher temperature, faster diffusion

Electrical or pressure gradientsElectrical or pressure gradients

Cell Membranes Show Selective Cell Membranes Show Selective PermeabilityPermeability

Some substances Some substances enter, but not othersenter, but not others

Vital to maintaining Vital to maintaining homeostasishomeostasis

Allows NPAllows NP Impermeable to Impermeable to

ions & lg Polarions & lg Polar

Section 5.5:Section 5.5:Osmosis Osmosis

Diffusion of water molecules across a Diffusion of water molecules across a selectively permeable membraneselectively permeable membrane

water molecules protein molecules

semipermeable membranebetween two compartments

• Direction of net flow is determined by water concentration gradient

• Side with the most solute molecules has the lowest water concentration

Tonicity Tonicity

Refers to Refers to relativerelative solute concentration of solute concentration of two fluidstwo fluids

HypotonicHypotonic - having fewer solutes - having fewer solutes

HypertonicHypertonic - having more solutes - having more solutes

IsotonicIsotonic - having same amount - having same amount

2% sucrose solution

1 liter of distilled water

1 liter of 10% sucrose

solution

1 liter of 2% sucrose

solution

HypotonicConditions

HypertonicConditions

IsotonicConditions

Fig. 5-13, p.85

Tonicity and Osmosis

What type of solution are these cells in?

A CB

Hypertonic Isotonic Hypotonic

Pressure and OsmosisPressure and Osmosis

Hydrostatic pressureHydrostatic pressure Pressure exerted by fluid on the walls that Pressure exerted by fluid on the walls that

contain itcontain it The greater the solute concentration of the The greater the solute concentration of the

fluid, the greater the hydrostatic pressurefluid, the greater the hydrostatic pressure Osmotic pressureOsmotic pressure

Amount of pressure necessary to prevent Amount of pressure necessary to prevent further increase of a solution’s volume further increase of a solution’s volume

How Organisms Deal How Organisms Deal with Osmotic Pressurewith Osmotic Pressure

•A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.

How organisms deal with How organisms deal with Osmotic PressureOsmotic Pressure

• Salt water fishSalt water fish pump salt out of their pump salt out of their specialized gillsspecialized gills so they do not dehydrate. so they do not dehydrate.

• Animal cellsAnimal cells are bathed in are bathed in blood. Kidneysblood. Kidneys keep the blood isotonic by remove excess salt keep the blood isotonic by remove excess salt and water.and water.

Bacteria and plantsBacteria and plants have have cell wallscell walls that that prevent them from over-expanding. In plants prevent them from over-expanding. In plants the pressure exerted on the cell wall is called the pressure exerted on the cell wall is called tugor pressure. tugor pressure.

Increase in Fluid VolumeIncrease in Fluid Volume

hypotonic solution

membrane permeable towater but not to solutes

hypertonicsolution

fluid volume rises in second compartment

second compartment

first compartment

Fig. 5.14, p.85

Section 5.4:Section 5.4:Passive Transport Passive Transport

Flow of solutes through the interior of Flow of solutes through the interior of passive transport proteins down their passive transport proteins down their concentration gradientsconcentration gradients

Passive transport proteins allow solutes to Passive transport proteins allow solutes to move both waysmove both ways

Does not require any energy inputDoes not require any energy input

Passive TransportPassive Transport

Stepped Art

glucose transporter

solute (glucose)

high

low

Fig. 5.10, p.80

Facilitated DiffusionFacilitated Diffusion

Help move specific solutes down the Help move specific solutes down the gradientgradient

Can be gatedCan be gated

Active TransportActive Transport

Net diffusion of solute is against Net diffusion of solute is against concentration gradientconcentration gradient

Transport protein must be activatedTransport protein must be activated ATP gives up phosphate to activate ATP gives up phosphate to activate

proteinprotein Binding of ATP changes protein shape Binding of ATP changes protein shape

and affinity for soluteand affinity for solute

ActiveActive

Help specific solutes diffuse against the Help specific solutes diffuse against the gradientgradient

Fig. 5-11, p.83

Active TransportActive Transport

ATP

ADP

Pi

higher calciumconcentration

Stepped Art

Active TransportActive Transport

ATP gives up phosphate to activate ATP gives up phosphate to activate proteinprotein

Binding of ATP changes protein Binding of ATP changes protein shape and affinity for soluteshape and affinity for solute

Types of Cellular TransportTypes of Cellular Transport

Passive TransportPassive Transport

cell doesn’t use energycell doesn’t use energy1.1. DiffusionDiffusion

2.2. Facilitated DiffusionFacilitated Diffusion

3.3. OsmosisOsmosis

Active TransportActive Transport

cell does use energycell does use energy1.1. Protein PumpsProtein Pumps

2.2. EndocytosisEndocytosis

3.3. ExocytosisExocytosis

high

low

This is gonna

be hard

work!!

high

low

Weeee!!!

•Animations of Active Transport

& Passive Transport

Other typesOther types

Fig. 5-9, p.81

Endocytosis (vesicles in)

Exocytosis (vesicles out)

Section 5.6:Section 5.6:Endocytosis and ExocytosisEndocytosis and Exocytosis

Exocytosis: A cytoplasmic vesicle fuses Exocytosis: A cytoplasmic vesicle fuses with the plasma membrane and contents with the plasma membrane and contents are released outside the cellare released outside the cell

EndocytosisEndocytosis

A small patch of plasma membrane sinks A small patch of plasma membrane sinks inward and seals back on itself, forming a inward and seals back on itself, forming a vesicle inside the cytoplasm – membrane vesicle inside the cytoplasm – membrane receptors often mediate this processreceptors often mediate this process

Fig 5.17, p.87

Macrophage engulfing Macrophage engulfing Leishmania mexicanaLeishmania mexicana

parasite macrophage

endocytosis exocytosis

coated pit

a

b

d c

ef

Fig. 5-15, p.86

5.6 Traffic to and From the

CellEndocytosis

and Exocytosis

endoplasmic reticulum

Golgi body

vesicle membrane fuses with plasma membrane

How Proteins Get to the SurfaceHow Proteins Get to the Surface

Fig. 5.18, pg. 87

Endocytosis of cholesterolEndocytosis of cholesterol

plasma membrane cholesterol