A Closer Look at Membranes Chapter 5. Cystic Fibrosis Caused by defective protein channel (CFTR) in...
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Transcript of A Closer Look at Membranes Chapter 5. Cystic Fibrosis Caused by defective protein channel (CFTR) in...
A Closer Look at A Closer Look at MembranesMembranes
Chapter 5Chapter 5
Cystic FibrosisCystic Fibrosis
• Caused by defective protein channel Caused by defective protein channel (CFTR) in epithelial cells(CFTR) in epithelial cells
• Not enough ClNot enough Cl-- and water cross and water cross membranesmembranes
• Thick mucus clogs airways and ducts Thick mucus clogs airways and ducts throughout bodythroughout body
• Usually fatal by age 30Usually fatal by age 30
• Main component Main component of cell membranesof cell membranes
• Gives membrane Gives membrane its fluid propertiesits fluid properties
• Fatty acid tails Fatty acid tails sandwiched sandwiched between between hydrophilic headshydrophilic heads
Lipid BilayerLipid Bilayer
Figure 5.2cPage 82
lipid bilayer
fluid fluid
Fluid Mosaic ModelFluid Mosaic Model
• Membrane is a mosaic ofMembrane is a mosaic of– PhospholipidsPhospholipids– GlycolipidsGlycolipids– SterolsSterols– ProteinsProteins
• Most phospholipids and some Most phospholipids and some
proteins can drift through membraneproteins can drift through membrane
Membrane ProteinsMembrane Proteins
active transporters
receptor protein
adhesionprotein
communicationprotein
passivetransporter
recognition protein
Figure 5.5 Page 85
Membrane ExperimentsMembrane Experiments
• Split membranes reveal embedded Split membranes reveal embedded proteinsproteins
In-text figurePage 86
• Hybrid human-mouse cell shows Hybrid human-mouse cell shows some proteins drift within membranesome proteins drift within membrane
Membrane ExperimentsMembrane Experiments
human cell mouse cell hybrid cell
Figure 5.6Page 86
Selective Permeability Selective Permeability
O2, CO2, and other small, nonpolar
molecules; some water molecules
glucose and other large, polar, water-soluable molecules; ions,
water molecules
Membrane Crossing Membrane Crossing MechanismsMechanisms
Diffusion across lipid bilayerDiffusion across lipid bilayer
Passive transportPassive transport
Active transportActive transport
EndocytosisEndocytosis
ExocytosisExocytosis
Concentration Gradient Concentration Gradient
• Means the number of molecules or Means the number of molecules or ions in one region is different than ions in one region is different than the number in another regionthe number in another region
• In the absence of other forces, a In the absence of other forces, a substance moves from a region substance moves from a region where it is more concentrated to one where it is more concentrated to one where it’s less concentrated - “down” where it’s less concentrated - “down” gradientgradient
DiffusionDiffusion
• The net movement of like molecules The net movement of like molecules or ions down a concentration or ions down a concentration gradientgradient
• Although molecules collide randomly, Although molecules collide randomly, the net movement is away from the the net movement is away from the place with the most collisions (down place with the most collisions (down gradient)gradient)
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
Example of DiffusionExample of Diffusion
• Span the lipid bilayerSpan the lipid bilayer
• Interior is able to open to both Interior is able to open to both sidessides
• Change shape when they interact Change shape when they interact with solute with solute
• Move water-soluble substances Move water-soluble substances across a membraneacross a membrane
Transport ProteinsTransport Proteins
Passive and Active Transport Passive and Active Transport
• Doesn’t require Doesn’t require energy inputs energy inputs
• Solutes diffuse Solutes diffuse through a channel through a channel inside the protein’s inside the protein’s interiorinterior
• Net movement is Net movement is down down concentration concentration gradientgradient
Passive Transport Active Transport
• Requires ATPRequires ATP
• Protein is an Protein is an ATPase pumpATPase pump
• Pumps solute Pumps solute against its against its concentration concentration gradientgradient
glucose transporter
solute (glucose)
high
low
Figure Figure 5.105.10Page 88Page 88
Stepped Art
Passive Transport
ATP
ADP
Pi
higher calcium concentration
lower calcium concentration
Figure 5.11Figure 5.11Page 89Page 89
Stepped Art
Active Transport
OsmosisOsmosis
• Water molecules tend to diffuse down Water molecules tend to diffuse down
water concentration gradientwater concentration gradient
• Total number of molecules or ions Total number of molecules or ions
dictates concentration of waterdictates concentration of water
• Tonicity - relative solute Tonicity - relative solute
concentrationsconcentrations
TonicityTonicity2% sucrose
solution
distilled water
10%sucrose solution
2%sucrose solution
Hypotonic Conditions
Hypertonic Conditions
Isotonic Conditions
Figure 5.13Page 90
Fluid PressureFluid Pressure
• Hydrostatic pressure Hydrostatic pressure
• Turgor pressure Turgor pressure
• Osmotic pressureOsmotic pressure
normal plant cells after plasmolysis
Endocytosis andEndocytosis and Exocytosis Exocytosis
plasma membrane
cytoplasm
cytoplasm
Exocytosis
Endocytosis
Endocytosis PathwaysEndocytosis Pathways
• Bulk phaseBulk phase
• Receptor-mediatedReceptor-mediated
• PhagocytosisPhagocytosis
clathrin Figures 5.17, 5.18Pages 92, 93
Membrane Membrane CyclingCycling
Exocytosis and Exocytosis and endocytosis endocytosis continually continually replace and replace and withdraw withdraw patches of patches of plasma plasma membranemembrane
lysosome
Golgibody
clathrin
Figure 5.19Page 93