membrane structure and function. phospholipids membranes are made of fat (lipids)
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Membrane structure and function
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Phospholipids
Membranes are made of fat (lipids)
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Hydrophilichead
Hydrophobictails
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Hydrophilichead
Hydrophobictail
WATER
WATER
Bilayer
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Bilayer
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Biological membranes are fluid mosaics of lipids and proteins
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Hydrophilic regionof protein
Hydrophobic region of protein
Phospholipidbilayer
Fluid Mosaic Model of Singer and Nicolson (1972)
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Freeze fracture (electron microscopy)
Evidence for fluid mosaic model
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Knife
Cytoplasmic layerExtracellular layer
Cytoplasmic layer
Plasmamembrane
Extracellular layer
Proteins
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Lateral movement(~107 times per second)
Flip-flop(~ once per month)
Movement of phospholipids
Membrane fluidity
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ViscousFluid
Unsaturated hydrocarbontails with kinks
Membrane fluidity
Saturated hydro-carbon tails
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Cholesterol
Cholesterol within the animal cell membrane
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Fibers ofextracellularmatrix (ECM)
Glycoprotein
Carbohydrate
Microfilamentsof cytoskeleton
Cholesterol
Integralprotein
Peripheralproteins
CYTOPLASMIC SIDEOF MEMBRANE
EXTRACELLULARSIDE OFMEMBRANE
Glycolipid
Membrane Proteins
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Fibers ofextracellularmatrix (ECM)
Glycoprotein
Carbohydrate
Microfilamentsof cytoskeleton
Cholesterol
Integralprotein
Peripheralproteins
CYTOPLASMIC SIDEOF MEMBRANE
EXTRACELLULARSIDE OFMEMBRANE
Glycolipid
Membrane Proteins
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EXTRACELLULARSIDEN-terminus
C-terminusCYTOPLASMICSIDE
Helix
Transmembrane protein
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EnzymesSignal
ReceptorATP
Transport Enzymatic activity Signal transduction
Membrane Proteins: functions
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Glyco-protein
Cell-cell recognition Intercellular joining Attachment to thecytoskeleton and extra-cellular matrix (ECM)
Membrane Proteins: functions
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• Passive transport
• Active transport
• Bulk transport
Moving stuff around
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Diffusion
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Molecules of dye Membrane (cross section)
WATER
Net diffusion Net diffusion Equilibrium
Diffusion of one solute
Passive Transport
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• Passive transport is the diffusion of a substance across a biological membrane
• No energy required
Passive Transport
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Lowerconcentrationof solute (sugar)
Higherconcentrationof sugar
Same concentrationof sugar
Selectivelypermeable mem-brane: sugar mole-cules cannot passthrough pores, butwater molecules can
H2O
Osmosis
Osmosis
Diffusion of water across a membrane
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Animalcell
Lysed
H2O H2O H2O
Normal
Hypotonic solution Isotonic solution Hypertonic solution
H2O
Shriveled
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Getting across the membrane
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Rather directly
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Exocytosis
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Some material can diffuse through membranes on their own
Diffusion
Passive
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Some materials diffuse through only with help
Diffusion
Passive
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Some materials must be pumped through membranes
Against Diffusion
Active (not passive)
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Diffusion Facilitated diffusion
Passive transport
ATP
Active transport