membrane structure and function ch 12, stryer short course
TRANSCRIPT
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Membrane Structure and FunctionCh 12, Stryer Short Course
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Introduction to Membranes
• Lipid structure makes a bilayer• Hydrophobic effect• Non-covalent structure
• Fluidity of membrane: liquid crystal• Fluidity controlled by
cholesterol, tail packing
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Fluidity
• Transverse vs lateral diffusion• Bleaching experiment• Fluid Mosaic Model
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Extremophiles• Archea: branched tails, ether linkages• Increased range of temperature• Stable to hydrolysis• Stable to oxidation
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Permeability
• Membrane impermeable to ions (water shell)• Mainly impermeable to larger
polar molecules• Water can flow slowly
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Introduction to Membrane Proteins• Proteins carry out
membrane function• Diversity of membranes
based on protein content
• Types of proteins• Integral proteins• Peripheral proteins• Anchored proteins
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Integral Proteins
• Common motifs• 7-transmembrane helix• b-barrel
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Anchored proteins• Reversible
Anchoring directs proteins to membrane• Patholgy• Cancer• Hutchinson-
Guilford Progeria syndrome
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Effect of Aspirin• Arachidonate from membrane, travels through
cavity in Prostaglandin H2 synthase• Aspirin covalently modifies Serine in
cyclooxygenase active site• COX-1 and COX-2 inhibitors
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Transporter Proteins
• Thermodynamic gradients• Concentration gradient• Ion gradient
• Pumps, channels, transporters• Diffusion• Simple diffusion• Facilitated diffusion (passive
transport)• Active Transport
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Sodium-Potassium ATPase• Up to a third of ATP is used to
create ion gradient• Maintain structure and function of
cell
• ATP phosphorylates the pump• Change in conformation used to
drive sodium/potassium exchange
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MechanismDigitalis blocks dephosphorylation, leading to low sodium ion gradient. This changes the calcium ion gradient, making the heart beat harder.
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ABC transporters
• ATP-binding cassette domain• Large superfamily includes
• Multidrug Resistance Pump• Cystic Fibrosis Transmembrane
Regulator• ATP-regulated chloride channel • Mutation causes less fluid/salt to
be pumped out of cell
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Secondary Transport
• Use energy of active transport to make a gradient• This gradient drives active
transport of another compound
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Facilitated transport: K+ channel
• Channels can allow specific compounds to transverse the membrane rapidly• Nerve Impulse• Controlled systems• Voltage gated• Ligand gated• mechanicoselective
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Structure explains specificity• How do you block a smaller
sodium ion from going through a hole that fits a larger potassium ion?• Make up for desolvation with
strong binding
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Structure explains speed
• Four binding sites in the narrow channel• Repulsion of
neighboring ions pushes potassium through