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•• Cells don’t live floating in fluid Cells don’t live floating in fluid –– must attach to must attach to surface and to each othersurface and to each other
•• Molecules secreted by cellsMolecules secreted by cells
•• Provide structural and biochemical support, Provide structural and biochemical support,
stiffness, and elasticitystiffness, and elasticity
•• Solutes are mostly polarSolutes are mostly polar
•• How do we keep molecules How do we keep molecules
where they need to be?where they need to be?
Cell Membrane StructureCell Membrane Structure
•• Solution: cell membrane must be fundamentally Solution: cell membrane must be fundamentally nonnon--polar, but able to exist in aqueous polar, but able to exist in aqueous
environmentenvironment
•• Molecule that makes this possible = Molecule that makes this possible = phospholipidphospholipid
Cell Membrane StructureCell Membrane Structure
•• Polar heads face both outside and insidePolar heads face both outside and inside
•• Hydrophilic heads face aqueous environmentsHydrophilic heads face aqueous environments
•• NonNon--polar tails protected in betweenpolar tails protected in between
Cell Membrane StructureCell Membrane Structure
•• Membrane must be very fluidMembrane must be very fluid
•• Fluidity adjusted by changing saturation of fatty Fluidity adjusted by changing saturation of fatty acid tailsacid tails
•• More saturated = less fluidMore saturated = less fluid
Cell Membrane StructureCell Membrane Structure
•• Problem: system is too effectiveProblem: system is too effective
•• Like a room with no doors and no windowsLike a room with no doors and no windows
•• How does anything get in or out?How does anything get in or out?
Cell Membrane StructureCell Membrane Structure
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•• Solution: membranes not 100% phospholipidSolution: membranes not 100% phospholipid
•• PhospholipidPhospholipid
•• CholesterolCholesterol
•• (Carbohydrate)(Carbohydrate)
•• ProteinsProteins
Cell Membrane StructureCell Membrane Structure
•• 50% dry weight of membrane50% dry weight of membrane
•• Carbohydrate chains on Carbohydrate chains on glycoproteinsglycoproteins provide provide “fingerprint”“fingerprint”
•• Cell can recognize self Cell can recognize self vsvs nonnon--selfself
•• Genetically determinedGenetically determined
Membrane Protein FunctionsMembrane Protein Functions
•• Proteins = major functional componentProteins = major functional component
Membrane ProteinsMembrane Proteins
•• Two configurationsTwo configurations
•• IntegralIntegral
•• Span entire width Span entire width
of membraneof membrane
•• Part of membranePart of membrane
structurestructure
•• PeripheralPeripheral
•• Bind to inner or Bind to inner or
outer surfacesouter surfaces
•• Distinct from membraneDistinct from membrane
Membrane ProteinsMembrane Proteins
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•• TransportersTransporters
•• ChannelsChannels
•• Integral proteinsIntegral proteins
•• Central poreCentral pore
•• Permits entry of small molecules, waterPermits entry of small molecules, water
Membrane Protein FunctionsMembrane Protein Functions
•• TransportersTransporters
•• CarriersCarriers
•• Bind solutes, transport across membraneBind solutes, transport across membrane
•• Protein changes shapeProtein changes shape
•• May or may not require ATPMay or may not require ATP
Membrane Protein FunctionsMembrane Protein Functions
•• EnzymesEnzymes
•• Can be integral or peripheralCan be integral or peripheral
•• Catalyze reactions inside and outside cellCatalyze reactions inside and outside cell
•• Example: membraneExample: membrane--associated enzymes in associated enzymes in small intestine break down small intestine break down dipeptidesdipeptides into into
amino acidsamino acids
Membrane Protein FunctionsMembrane Protein Functions
•• ReceptorsReceptors
•• Bind to external chemicals to regulate Bind to external chemicals to regulate processes within cellprocesses within cell
•• ShapeShape--specificspecific
•• Not necessary forNot necessary for
steroid hormonessteroid hormones
•• Example: insulinExample: insulin
(peptide hormone)(peptide hormone)
Membrane Protein FunctionsMembrane Protein Functions
•• AnchorsAnchors
•• IntercellularIntercellular
•• Attach cells to each otherAttach cells to each other
Membrane Protein FunctionsMembrane Protein Functions