plasma membrane
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The Plasma The Plasma MembraneMembrane -
Gateway to the CellGateway to the Cellcopyright cmassengale
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Photograph of a Cell Photograph of a Cell MembraneMembrane
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Cell MembraneCell Membrane
The cell membrane is flexibleflexible and allows a unicellular organism to move
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HomeostasisHomeostasis
•Balanced internal condition of cells
•Also called equilibrium•Maintained by plasma
membrane controlling what enters & leaves the cell
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Functions of Plasma Functions of Plasma MembraneMembrane
Protective barrierProtective barrier
Regulate transport in & out of Regulate transport in & out of cell cell (selectively permeable)(selectively permeable)
Allow cell recognitionAllow cell recognition
Provide anchoring sites for Provide anchoring sites for filaments filaments of cytoskeletonof cytoskeleton
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Functions of Plasma Functions of Plasma MembraneMembrane
Provide a binding site for Provide a binding site for enzymesenzymes
Interlocking surfaces bind cells Interlocking surfaces bind cells together (junctions)together (junctions)
Contains the cytoplasm (fluid in Contains the cytoplasm (fluid in cell) cell)
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Structure of the Structure of the Cell MembraneCell Membrane
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PhospholipidsPhospholipids
CholesterolCholesterol
Proteins(peripheral and integral)Carbohydrates (glucose)
Membrane ComponentsMembrane Components
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PhospholipidsPhospholipids
Make up the cell membrane
Contains 2 fatty acid chains that are nonpolarHead is polar & contains a –PO4 group & glycerol copyright cmassengale
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FLUIDFLUID- because individual phospholipids and - because individual phospholipids and proteins can move side-to-side within the proteins can move side-to-side within the layer, like it’s a liquid.layer, like it’s a liquid.
MOSAICMOSAIC- because of the pattern produced by - because of the pattern produced by the scattered protein molecules when the the scattered protein molecules when the membrane is viewed from abovemembrane is viewed from above..
FLUID MOSAIC MODELFLUID MOSAIC MODEL
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Polar heads are hydrophilichydrophilic “water loving”Nonpolar tails are hydrophobichydrophobic “water fearing”
Cell MembraneCell Membrane
Makes membrane “Selective” in what crosses
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Cell MembraneCell Membrane
Hydrophobic molecules pass easily; hydrophilic DO NOT
The cell membrane is made of 2 layers of phospholipidphospholipids called the lipid bilayerbilayer
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SolubilitySolubility•Materials
that are soluble in lipids can pass through the cell membrane easily
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Small molecules and larger hydrophobic molecules move through easily.e.g. O2, CO2, H2O
Semipermeable Semipermeable MembraneMembrane
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Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.
Semipermeable Semipermeable MembraneMembrane
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Types of Transport Types of Transport Across Cell Across Cell MembranesMembranes
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Simple DiffusionSimple Diffusion
• Requires NONO energy
• Molecules move from area of HIGH HIGH to LOWto LOW concentration
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DIFFUSIONDIFFUSION
Diffusion is a PASSIVEPASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY
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Diffusion of LiquidsDiffusion of Liquids
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Diffusion through a Diffusion through a MembraneMembrane
Cell membrane
Solute moves DOWN concentration gradient (HIGH to LOW)copyright cmassengale
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OsmosisOsmosis• Diffusion of Diffusion of
waterwater across a across a membranemembrane
• Moves fromMoves from HIGH water HIGH water potentialpotential (low (low solute) tosolute) to LOW LOW water potentialwater potential (high solute)(high solute)
Diffusion across a membrane
Semipermeable
membrane
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Diffusion of HDiffusion of H22O Across O Across A MembraneA Membrane
High H2O potentialLow solute concentration
Low H2O potentialHigh solute concentration
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AquaporinsAquaporins• Water Channels• Protein pores used during
OSMOSISWATERMOLECULES
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Cell in Isotonic SolutionCell in Isotonic Solution
CELLCELL
10% NaCL90% H2O
10% NaCL
90% H2O
What is the direction of water movement?The cell is at _______________.equilibrium
ENVIRONMENTENVIRONMENT
NO NET NO NET MOVEMENMOVEMENTT
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Cell in Hypotonic Cell in Hypotonic SolutionSolution
CELLCELL
10% NaCL90% H2O
20% NaCL
80% H2O
What is the direction of water movement? copyright cmassengale
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Cell in Hypertonic Cell in Hypertonic SolutionSolution
CELLCELL
15% NaCL85% H2O
5% NaCL95% H2O
What is the direction of water movement?
ENVIRONMENTENVIRONMENT
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Cells in SolutionsCells in Solutions
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Isotonic Solution
NO NET MOVEMENT OF
H2O (equal amounts entering
& leaving)
Hypotonic Solution
CYTOLYSIS
Hypertonic Solution
PLASMOLYSIS
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Cytolysis & PlasmolysisCytolysis & Plasmolysis
Cytolysis Plasmolysis
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Osmosis in Red Blood Osmosis in Red Blood CellsCells
IsotonicIsotonic Hypotonic
Hypertoniccopyright cmassengale
What Happens to Blood Cells?
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hypotonic hypertonic isotonic
hypertonic isotonic hypotonic
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Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane
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Passive Passive TransportTransport
Simple DiffusionSimple Diffusion
Doesn’tDoesn’t require require energyenergy
Moves Moves high to lowhigh to low concentrationconcentration Example: Example: OxygenOxygen or or waterwater diffusing into a diffusing into a cell and cell and carbon carbon dioxidedioxide diffusing out diffusing out.
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Passive Passive TransportTransport
Facilitated diffusion
Doesn’t require energy
Uses transport proteins to move high to low concentrationExamples: Examples: GlucoseGlucose or or amino acidsamino acids moving moving from blood into a from blood into a cell.cell.
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Proteins Are Critical to Proteins Are Critical to Membrane FunctionMembrane Function
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Types of Transport Types of Transport ProteinsProteins
• Channel proteins are embedded in the cell membrane & have a pore for materials to cross
• Carrier proteins can change shape to move material from one side of the membrane to the other
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Facilitated DiffusionFacilitated Diffusion
Molecules will randomly move Molecules will randomly move through the through the porespores in in Channel Channel ProteinsProteins..
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Facilitated DiffusionFacilitated Diffusion
• SomeSome Carrier Carrier proteinsproteins do not do not extend through the extend through the membrane.membrane.
• They They bond and bond and drag moleculesdrag molecules through the lipid through the lipid bilayer and release bilayer and release them on the them on the opposite side.opposite side.
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Carrier ProteinsCarrier Proteins• Other carrier Other carrier
proteins proteins change shapechange shape to move to move materials materials across the cell across the cell membranemembrane
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Active TransportActive Transport
Requires energy or ATP
Moves materials from LOW to HIGH concentration
AGAINST concentration gradient
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Active transportActive transport
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
Called Na+-K+ Pump
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Sodium-Potassium Sodium-Potassium PumpPump
3 Na+ pumped in for every 2 K+ pumped out; creates a membrane
potential
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Moving the “Big Stuff”Moving the “Big Stuff”
Molecules are Molecules are moved outmoved out of the cell by of the cell by vesiclesvesicles that that fusefuse with the plasma membrane. with the plasma membrane.
ExocytosExocytosisis-
moving things out.
This is how many This is how many hormoneshormones are secreted and how are secreted and how nerve cellsnerve cells communicate with one another communicate with one another.
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ExocytosisExocytosisExocytic Exocytic vesicle vesicle immediately immediately after fusion after fusion with plasma with plasma membrane.membrane.
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Moving the “Big Moving the “Big Stuff”Stuff”Large molecules move materials into the Large molecules move materials into the
cell by one of cell by one of three forms of endocytosisthree forms of endocytosis.
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PinocytosisPinocytosis
Most Most commoncommon form of endocytosis form of endocytosis. Takes in Takes in dissolveddissolved molecules as a molecules as a vesiclevesicle.
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PinocytosisPinocytosis
• Cell forms an Cell forms an invaginationinvagination
• Materials Materials dissolve in dissolve in waterwater to be to be brought into brought into cellcell
• Called Called “Cell “Cell Drinking”Drinking”
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Example of Example of PinocytosisPinocytosispinocytic vesicles forming mature transport vesicle
Transport across a capillary cell (blue).copyright cmassengale
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Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis
Some Some integral proteinsintegral proteins have have receptorsreceptors on their surface to on their surface to recognize & take in recognize & take in hormones, hormones, cholesterolcholesterol, etc., etc.
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Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis
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Endocytosis – Phagocytosis Endocytosis – Phagocytosis
Used to Used to engulf large particlesengulf large particles such such as food, as food, bacteriabacteria, etc. into vesicles, etc. into vesicles
Called Called “Cell Eating”“Cell Eating”copyright cmassengale
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Phagocytosis About to OccurPhagocytosis About to Occur
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PhagocytoPhagocytosissis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)
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ExocytosisExocytosis The opposite of endocytosis is exocytosis. The opposite of endocytosis is exocytosis. Large moleculesLarge molecules that are manufactured in that are manufactured in
the cell are the cell are releasedreleased through the cell through the cell membranemembrane..
Inside Cell Cell environment
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