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