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Membrane structure and function. Membranes are made of fat (lipids). Phospholipids. Hydrophilic head. Hydrophobic tails. WATER. Hydrophilic head. Hydrophobic tail. WATER. Bilayer. Bilayer. Biological membranes are fluid mosaics of lipids and proteins. Hydrophilic region
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Membranes are made of fat (lipids) Phospholipids
Hydrophilic head Hydrophobic tails
WATER Hydrophilic head Hydrophobic tail WATER Bilayer
Biological membranes are fluid mosaics of lipids and proteins
Hydrophilic region of protein Phospholipid bilayer Hydrophobic region of protein Fluid Mosaic Model of Singer and Nicolson (1972)
Evidence for fluid mosaic model Freeze fracture (electron microscopy)
Extracellular layer Proteins Knife Plasma membrane Cytoplasmic layer Extracellular layer Cytoplasmic layer
Lateral movement (~107 times per second) Flip-flop (~ once per month) Movement of phospholipids Membrane fluidity
Viscous Fluid Saturated hydro- carbon tails Unsaturated hydrocarbon tails with kinks Membrane fluidity
Cholesterol Cholesterol within the animal cell membrane
Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Peripheral proteins Microfilaments of cytoskeleton Integral protein CYTOPLASMIC SIDE OF MEMBRANE Membrane Proteins
Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Peripheral proteins Microfilaments of cytoskeleton Integral protein CYTOPLASMIC SIDE OF MEMBRANE Membrane Proteins
EXTRACELLULAR SIDE N-terminus C-terminus CYTOPLASMIC SIDE a Helix Transmembrane protein
Membrane Proteins: functions Signal Enzymes Receptor ATP Enzymatic activity Transport Signal transduction
Membrane Proteins: functions Glyco- protein Attachment to the cytoskeleton and extra- cellular matrix (ECM) Cell-cell recognition Intercellular joining
Moving stuff around • Passive transport • Active transport • Bulk transport
Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium Diffusion of one solute Passive Transport
Passive Transport • Passive transport is the diffusion of a substance across a biological membrane • No energy required
Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar H2O Selectively permeable mem- brane: sugar mole- cules cannot pass through pores, but water molecules can Osmosis Osmosis Diffusion of water across a membrane
Isotonic solution Hypertonic solution Hypotonic solution Animal cell H2O H2O H2O H2O Shriveled Normal Lysed
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)
Passive transport Active transport ATP Facilitated diffusion Diffusion