Microsoft Power Point 05_A Closer Look Membranes[1]

8/14/2019 Microsoft Power Point 05_A Closer Look Membranes[1]

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A Closer Look at MembranesA Closer Look at Membranes

Chapter 5Chapter 5


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Cystic FibrosisCystic Fibrosis


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Cystic FibrosisCystic Fibrosis

Caused by defective protein channelCaused by defective protein channel(CFTR) in epithelial cells(CFTR) in epithelial cells

-- membranesmembranes

Thick mucus clogs airways and ductsThick mucus clogs airways and ducts

throughout bodythroughout body Usually fatal by age 30Usually fatal by age 30


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Main component ofMain component ofcell membranescell membranes

Lipid BilayerLipid Bilayer

lipid

fluid propertiesfluid properties

Fatty acid tailsFatty acid tails

sandwichedsandwichedbetween hydrophilicbetween hydrophilicheadsheads

Figure 5.2cPage 82

bilayer

fluid fluid


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Fluid Mosaic ModelFluid Mosaic Model

Membrane is a mosaic ofMembrane is a mosaic of PhospholipidsPhospholipids

SterolsSterols

ProteinsProteins

Most phospholipids and some proteins canMost phospholipids and some proteins candrift through membranedrift through membrane


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Membrane ProteinsMembrane Proteins

receptorprotein

adhesionprotein recognition

protein

active transporters

communicationprotein passivetransporter

Figure 5.5Page 85


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Question 1Question 1

1. What is a lipid bilayer?1. What is a lipid bilayer?


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Answer 1Answer 1

1. What is a lipid bilayer?1. What is a lipid bilayer?

. .. .phospholipids oriented so that thephospholipids oriented so that thetails intermingle.tails intermingle.


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2. Name three types of proteins found in2. Name three types of proteins found inplasma membranes.plasma membranes.


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Answer 2Answer 2

2. Name three types of proteins found in2. Name three types of proteins found inplasma membranes.plasma membranes.

transport, receptor, recognition,transport, receptor, recognition,adhesive, and communicativeadhesive, and communicative

proteinsproteins


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Membrane ExperimentsMembrane Experiments

Split membranes reveal embeddedSplit membranes reveal embeddedproteinsproteins

In-text figure

Page 86


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Hybrid humanHybrid human--mouse cell shows somemouse cell shows someproteins drift within membraneproteins drift within membrane

Membrane ExperimentsMembrane Experiments

human cell mouse cell hybrid cell

Figure 5.6Pa e 86


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3. What do hybrid human mouse3. What do hybrid human mousemembranes show?membranes show?


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Answer 3Answer 3

3. What do hybrid human mouse cells3. What do hybrid human mouse cellsshow?show?

Hybrid humanHybrid human--mouse cell showsmouse cell showssome proteins drift withinsome proteins drift within

membrane.membrane.


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Selective PermeabilitySelective Permeability

O2, CO2,and other small, nonpolarmolecules; some water

molecules

glucose and other large, polar,water-soluable molecules; ions,water molecules


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Membrane Crossing MechanismsMembrane Crossing Mechanisms

Diffusion across lipid bilayerDiffusion across lipid bilayer

Passive transportPassive transport

Active transportActive transport

EndocytosisEndocytosis

ExocytosisExocytosis


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Concentration GradientConcentration Gradient

Means the number of molecules or ions inMeans the number of molecules or ions inone region is different than the number inone region is different than the number inanother regionanother region

In the absence of other forces, aIn the absence of other forces, asubstance moves from a region where it issubstance moves from a region where it is

more concentrated to one where its lessmore concentrated to one where its lessconcentratedconcentrated -- down gradientdown gradient


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DiffusionDiffusion

The net movement of like molecules orThe net movement of like molecules orions down a concentration gradientions down a concentration gradient

Although molecules collide randomly, theAlthough molecules collide randomly, thenet movement is away from the place withnet movement is away from the place with

the most collisions (down gradient)the most collisions (down gradient)


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Factors AffectingFactors AffectingDiffusion RateDiffusion Rate

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

Smaller molecules, faster diffusionSmaller molecules, faster diffusion

TemperatureTemperature

Higher temperature, faster diffusionHigher temperature, faster diffusion

Electrical or pressure gradientsElectrical or pressure gradients


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Example of DiffusionExample of Diffusion


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4. What is meant by the term, selectively4. What is meant by the term, selectivelypermeable?permeable?


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Answer 4Answer 4

4. What is meant by the term, selectively4. What is meant by the term, selectivelypermeable?permeable?

molecules to cross it, but blocks others.molecules to cross it, but blocks others.


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5. What molecules can easily pass across5. What molecules can easily pass acrossthe plasma membrane (with nothe plasma membrane (with noassistance ?assistance ?


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Answer 5.Answer 5.

5. What molecules can easily pass across5. What molecules can easily pass acrossthe plasma membrane (with nothe plasma membrane (with noassistance ?assistance ?

Small nonpolar molecules and someSmall nonpolar molecules and some

water. (ex. Oxygen, carbon dioxidewater. (ex. Oxygen, carbon dioxide


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Span the lipid bilayerSpan the lipid bilayer Interior is able to open to both sidesInterior is able to open to both sides

Transport ProteinsTransport Proteins

solutesolute

Move waterMove water--soluble substances acrosssoluble substances across

a membranea membrane


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Passive and Active TransportPassive and Active Transport

Doesnt requireDoesnt requireenergy inputsenergy inputs

Passive Transport Active Transport Requires ATPRequires ATP

Solutes diffuseSolutes diffuse

through a channelthrough a channelinside the proteinsinside the proteins

interiorinterior Net movement isNet movement is

down concentrationdown concentration

gradientgradient

pumppump Pumps solute againstPumps solute against

its concentrationits concentration

gradientgradient


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glucose transporter

solute (glucose) high

low

Passive Transport

Figure 5.10Figure 5.10Page 88Page 88

Stepped Art


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ATP

higher calciumconcentration

lower calcium concentration

Active Transport

ADP

Pi

Figure 5.11Figure 5.11Page 89Page 89

Stepped Art


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OsmosisOsmosis

Water molecules tend to diffuse downWater molecules tend to diffuse down

water concentration gradientwater concentration gradient

Total number of molecules or ionsTotal number of molecules or ions

dictates concentration of waterdictates concentration of water

TonicityTonicity -- relative solute concentrationsrelative solute concentrations


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TonicityTonicity2% sucrosesolution

distilled water

10%sucrosesolution

2%sucrose

solution

HypotonicConditions

HypertonicConditions

IsotonicConditions

Figure 5.13

Page 90


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Fluid PressureFluid Pressure

Hydrostatic pressureHydrostatic pressure Turgor pressureTurgor pressure


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PressuresPressures

''TurgorTurgor pressurepressure' or turgidity is the' or turgidity is themainmain pressurepressure of the cell contentsof the cell contentsa ainst the cell wall in lant cells anda ainst the cell wall in lant cells and

bacteria cells, determined by the waterbacteria cells, determined by the watercontent of the vacuole, resulting fromcontent of the vacuole, resulting fromosmoticosmotic pressurepressure, i.e. the, i.e. the hydrostatichydrostatic

pressurepressure produced by a solution in aproduced by a solution in aspace divided by aspace divided by a semipermeablesemipermeablemembrane.membrane.http://en.wikipedia.org/wiki/Turgor_pressurehttp://en.wikipedia.org/wiki/Turgor_pressure


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Endocytosis andEndocytosis andExocytosisExocytosis

plasma membrane

cytoplasm

Exocytosis

cytoplasm

Endocytosis


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Endocytosis PathwaysEndocytosis Pathways

Bulk phaseBulk phase ReceptorReceptor--mediatedmediated

clathrin Figures 5.17, 5.18

Pages 92, 93


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MembraneMembraneCyclingCycling

Exocytosis andExocytosis andendocytosisendocytosis

clathrin

con nua y rep acecon nua y rep aceand withdrawand withdrawpatches of plasmapatches of plasma

membranemembrane

lysosome

Golgibody

Figure 5.19

Page 93

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Microsoft Power Point 05_A Closer Look Membranes[1]