powerlecture: chapter 5 a closer look at cell membranes
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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
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
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
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
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