Plasma membrane, structure and function
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The plasma membrane forms a boundary around cells and controls what enters and exits. It is made of a phospholipid bilayer, proteins, and cholesterol. The bilayer forms a fluid mosaic with phospholipids providing structure and proteins facilitating functions like transport. Transport across the membrane includes passive diffusion of lipids and active transport of ions and molecules using protein carriers fueled by energy. Endocytosis and exocytosis move larger particles in and out using vesicles. Cell junctions allow communication between animal and plant cells.
![Transport ProcessesTransport Processes
• Movement of substances across theMovement of substances across the
cell membranecell membrane
• Passive transportPassive transport
– Substances move from [high]Substances move from [high][low][low]
– No energy input requiredNo energy input required
– Simple Diffusion, Facilitated Diffusion,Simple Diffusion, Facilitated Diffusion,
OsmosisOsmosis
• Active transportActive transport
– Substances move from [low]Substances move from [low][high][high]
– Requires energy inputRequires energy input
– Protein carriers, Endocytosis, ExocytosisProtein carriers, Endocytosis, Exocytosis](https://image.slidesharecdn.com/plasmamembranestructureandfunction-171024120105/85/Plasma-membrane-structure-and-function-11-320.jpg)
![OsmosisOsmosis
• Diffusion of water across aDiffusion of water across a
differentially permeable membranedifferentially permeable membrane
• Water moves from [high]Water moves from [high] [low][low]](https://image.slidesharecdn.com/plasmamembranestructureandfunction-171024120105/85/Plasma-membrane-structure-and-function-15-320.jpg)
![Applying Your KnowledgeApplying Your Knowledge
A.A. Which methods allow movement intoWhich methods allow movement into
the cell?the cell?
B.B. Which methods involve movement ofWhich methods involve movement of
liquid?liquid?
C.C. Which methods involve movementWhich methods involve movement
from [low]from [low] [high]?[high]?
1.1. Facilitated DiffusionFacilitated Diffusion
2.2. EndocytosisEndocytosis
3.3. OsmosisOsmosis
4.4. ExocytosisExocytosis
5.5. Active TransportActive Transport
6. Simple Diffusion6. Simple Diffusion
7. Pinocytosis7. Pinocytosis
8. Receptor-mediated8. Receptor-mediated
endocytosisendocytosis
9. Phagocytosis9. Phagocytosis
1, 2, 3, 5, 6, 7, 8, 91, 2, 3, 5, 6, 7, 8, 9
2, 3, 6, 72, 3, 6, 7
2, 4, 5, 7, 8, 92, 4, 5, 7, 8, 9](https://image.slidesharecdn.com/plasmamembranestructureandfunction-171024120105/85/Plasma-membrane-structure-and-function-25-320.jpg)
Plasma membrane, structure and function
- 1. Plasma MembranePlasma Membrane Structure and FunctionStructure and Function ByBy Rizwan Abbas BahoRizwan Abbas Baho
- 2. OligosaccharidesOligosaccharides CytoplasmCytoplasm Membrane ProteinsMembrane Proteins CholesterolCholesterol OuterOuter SurfaceSurface Fluid Mosaic ModelFluid Mosaic Model of Membrane Structureof Membrane Structure PhospholipidPhospholipid BilayerBilayer
- 3. Macromolecules found inMacromolecules found in MembranesMembranes • LipidsLipids – Phospholipid bilayerPhospholipid bilayer – CholesterolCholesterol • ProteinsProteins – Transport proteinsTransport proteins – Receptor proteinsReceptor proteins – Recognition proteinsRecognition proteins • CarbohydratesCarbohydrates – Oligosaccharides on glycoproteinsOligosaccharides on glycoproteins
- 4. Phospholipid StructurePhospholipid Structure FattyAcid FattyAcid Glycerol Polar groupPolar groupGlycerol FattyAcid FattyAcid FattyAcid Change fromChange from Triglyceride toTriglyceride to PhospholipidPhospholipid
- 5. The plasma membrane “fluid” isThe plasma membrane “fluid” is a double layer of phospholipids.a double layer of phospholipids.
- 6. The plasma membrane “mosaic” isThe plasma membrane “mosaic” is a collection of proteins.a collection of proteins.
- 7. Functions of MembraneFunctions of Membrane MacromoleculesMacromolecules • LipidsLipids – Phospholipid bilayerPhospholipid bilayer • Forms boundary to isolate cell contents fromForms boundary to isolate cell contents from environmentenvironment • Restricts passage of hydrophilic substancesRestricts passage of hydrophilic substances across the membraneacross the membrane – CholesterolCholesterol • Increases bilayer strength, flexibilityIncreases bilayer strength, flexibility • Reduces membrane fluidityReduces membrane fluidity • Reduces permeability to water-solubleReduces permeability to water-soluble substancessubstances
- 8. Functions of MembraneFunctions of Membrane MacromoleculesMacromolecules • ProteinsProteins – Transport proteinsTransport proteins • Regulate movement of water soluble substancesRegulate movement of water soluble substances – Channel proteins have pores that allowChannel proteins have pores that allow passage of ions and small water-solublepassage of ions and small water-soluble moleculesmolecules – Carrier proteins bind to molecules andCarrier proteins bind to molecules and change shape for delivery across membranechange shape for delivery across membrane
- 9. Functions of MembraneFunctions of Membrane MacromoleculesMacromolecules • ProteinsProteins – Receptor proteinsReceptor proteins • Docking site for molecules outside the cellDocking site for molecules outside the cell • Trigger internal cellular responseTrigger internal cellular response – Recognition proteinsRecognition proteins • Identification tagsIdentification tags – Oligosaccharides aid inOligosaccharides aid in cell-cell recognitioncell-cell recognition • Cell-surface attachmentCell-surface attachment sitessites
- 10. Applying Your KnowledgeApplying Your Knowledge A.A. Which component would have anWhich component would have an oligosaccharide attached?oligosaccharide attached? B.B. Which component regulates membraneWhich component regulates membrane fluidity?fluidity? C.C. Which component assists in movement ofWhich component assists in movement of water-soluble substances across thewater-soluble substances across the membrane?membrane? 1.1. CholesterolCholesterol 2.2. Receptor ProteinReceptor Protein 3.3. Phospholipid BilayerPhospholipid Bilayer 4.4. Transport ProteinTransport Protein 5.5. Recognition ProteinRecognition Protein
- 11. Transport ProcessesTransport Processes • Movement of substances across theMovement of substances across the cell membranecell membrane • Passive transportPassive transport – Substances move from [high]Substances move from [high][low][low] – No energy input requiredNo energy input required – Simple Diffusion, Facilitated Diffusion,Simple Diffusion, Facilitated Diffusion, OsmosisOsmosis • Active transportActive transport – Substances move from [low]Substances move from [low][high][high] – Requires energy inputRequires energy input – Protein carriers, Endocytosis, ExocytosisProtein carriers, Endocytosis, Exocytosis
- 12. Diffusion of Dye in WaterDiffusion of Dye in Water Time 0Time 0 SteepSteep ConcentrationConcentration GradientGradient Time 1Time 1 ReducedReduced ConcentrationConcentration GradientGradient DispersingDispersing Time 2Time 2 NoNo ConcentrationConcentration GradientGradient RandomRandom DispersalDispersal
- 13. Simple DiffusionSimple Diffusion (extracellular fluid) (cytoplasm) Some moleculesSome molecules diffuse freelydiffuse freely acrossacross (lipid soluble molecules, CO(lipid soluble molecules, CO22, O, O22, H, H22O )O ) Now known to require transport proteins called aquaporins
- 14. Facilitated Diffusion:Facilitated Diffusion: Use of Carriers to Assist with DiffusionUse of Carriers to Assist with Diffusion Carrier protein has binding site for molecule Molecule enters binding site Carrier protein changes shape, transporting molecule across membrane Carrier protein resumes original shape (Inside Cell)(Inside Cell)(Inside Cell)(Inside Cell) (Outside(Outside Cell)Cell) (Outside(Outside Cell)Cell) DiffusionDiffusion ChannelChannel ProteinProtein DiffusionDiffusion GradientGradient Molecule inMolecule in TransitTransit
- 15. OsmosisOsmosis • Diffusion of water across aDiffusion of water across a differentially permeable membranedifferentially permeable membrane • Water moves from [high]Water moves from [high] [low][low]
- 16. “Bound” water molecules clustered around sugar: cannot fit through pore “Free” water molecule: can fit through pore
- 17. Normal RBCs Isotonic SolutionIsotonic Solution The Effects of OsmosisThe Effects of Osmosis Equal movement of water into and out of cells Net movement of water out of cells Net movement of water into cells Shriveled RBCs Swollen RBCs Hypertonic SolutionHypertonic Solution Hypotonic SolutionHypotonic Solution
- 18. Active Transport with Protein CarrierActive Transport with Protein Carrier Inside CellInside CellInside CellInside Cell Outside CellOutside CellOutside CellOutside Cell EnergyEnergy ProviderProvider Spent EnergySpent Energy ProviderProvider TransportedTransported MoleculeMolecule 1 2 3 4
- 19. EndocytosisEndocytosis (extracellular fluid) Pinocytosis vesicle containing extracellular fluid)(cytoplasm) 1 2 33 cell (extracellular fluid) (cytoplasm) 1 2 33 44 coated pit forming Receptor-mediated Endocytosis Phagocytosis coated vesicle nutrients receptors food particle pseudopod particle enclosed in food vacuole
- 20. EndocytosisEndocytosis • Active process for movement ofActive process for movement of large molecules and organismslarge molecules and organisms – Substance is taken in by vesicleSubstance is taken in by vesicle formed from cell membraneformed from cell membrane – Phagocytosis: solid substance inPhagocytosis: solid substance in vesiclevesicle – Pinocytosis: liquid droplets in vesiclePinocytosis: liquid droplets in vesicle – Receptor-Mediated Endocytosis:Receptor-Mediated Endocytosis: incoming substance binds to receptorincoming substance binds to receptor
- 21. Receptor-mediated Endocytosis IReceptor-mediated Endocytosis I Begins with a shallowBegins with a shallow pit in plasma membranepit in plasma membrane Pit is coated withPit is coated with proteinprotein (cytoplasm) (extracellular fluid) coated pit protein coating extracellular particles bound to receptors plasma membrane Pit deepensPit deepens aa bb 0.1 Micrometer
- 22. Receptor-mediated Endocytosis IIReceptor-mediated Endocytosis II Pit deepens further andPit deepens further and begins to pinch offbegins to pinch off Eventually becomes aEventually becomes a coated vesiclecoated vesicle ddcc 0.1 Micrometer coated vesicle
- 23. ExocytosisExocytosis • Substance is expelled after beingSubstance is expelled after being enclosed in a vesicle within the cellenclosed in a vesicle within the cell • Used to move large molecules outUsed to move large molecules out of the cellof the cell
- 25. Applying Your KnowledgeApplying Your Knowledge A.A. Which methods allow movement intoWhich methods allow movement into the cell?the cell? B.B. Which methods involve movement ofWhich methods involve movement of liquid?liquid? C.C. Which methods involve movementWhich methods involve movement from [low]from [low] [high]?[high]? 1.1. Facilitated DiffusionFacilitated Diffusion 2.2. EndocytosisEndocytosis 3.3. OsmosisOsmosis 4.4. ExocytosisExocytosis 5.5. Active TransportActive Transport 6. Simple Diffusion6. Simple Diffusion 7. Pinocytosis7. Pinocytosis 8. Receptor-mediated8. Receptor-mediated endocytosisendocytosis 9. Phagocytosis9. Phagocytosis 1, 2, 3, 5, 6, 7, 8, 91, 2, 3, 5, 6, 7, 8, 9 2, 3, 6, 72, 3, 6, 7 2, 4, 5, 7, 8, 92, 4, 5, 7, 8, 9
- 26. Cell Attachment StructuresCell Attachment Structures DesmosomeDesmosome desmosome Protein strands holding cells together Protein filaments in cytoplasm Small intestine Plasma membrane (edge view) Cells lining small intestine Tight JunctionTight Junction Tight junctions formed by strands of protein Plasma membrane (edge view) Cells lining bladder Tight junctions seal membranes of adjacent cells together
- 27. Cell Communication StructuresCell Communication Structures Gap JunctionsGap Junctions desmosome Gap Junctions: pairs of channels connect insides of adjacent cells Liver Plasma membrane (edge view) Liver cells PlasmodesmataPlasmodesmata Plasmodesmata connect insides of adjacent cells Plasma membrane (edge view) Root cells Cell wall (edge view) Middle lamella (edge view) Root AnimalsAnimals PlantsPlants
Editor's Notes
- #3: Many of these protein molecules (blue in this illustration) float around in the membrane like icebergs on the polar sea. The proteins serve several functions: Transport proteins: Regulate the movement of water-soluble molecules through the plasma membrane. Channel Proteins: Form pores that allow small molecules to pass. Carrier Proteins: Have binding sites that bind specifically to specific proteins and move the molecules through the membrane. Receptor Proteins: Trigger specific cellular responses when certain molecules bind to them. Recognition Proteins: Serve as ID tags and cell-surface attachment sites.
- #5: A triglyceride is a glycerol molecule with three fatty acids attached (p42). Triglycerides are familiar fats and oils. The fatty acids may be of the same type or different types. Different fatty acids may have differing number of carbon atoms in their hydrocarbon chain. Some fatty acids have double bonds and are called unsaturated. Those with no double bonds are called saturated. Phosphoplipids are like triglycerides with one fatty acid swapped out and a polar group containing phosphorous swapped in its place. Phospholipids are abundant in biological membranes. They self assemble into lipid bilayers characteristic of the plasma membrane and organnelle membranes (fig 5-2).
- #6: Eukaryotic Cell
- #7: Eukaryotic Cell
- #12: This refers to the types of processes used by cells to get materials in and out across the cell membrane. The membrane is said to be “semi-permeable.” This means that it will allow spontaneous passage of some materials but others must use special processes to get across. A concentration gradient is a difference in the number of molecules or ions of a given substance in two adjoining regions. Molecules constantly collide and tend to move according to existing concentration gradients. The net movement of like molecules down a concentration gradient (high to low) is simple diffusion. Gradients in temperature, electric charge, and pressure, can influence movements. Passive transport: Follows a concentration gradient Passive in the sense that the process does not require energy. It just happens naturally. Diffusion is passive transport. Due to the random movement of molecules in liquids & gases (Brownian motion). A concentrated material will tend to become more uniformly dispersed in the space made available to it. Water can diffuse across the cell membrane unassisted. Facilitated transport: Also follows a concentration gradient, but requires gateway to get through. In this case, the particular materials would not spontaneously cross the pure phospholipid membrane, even if encouraged by a concentration gradient. A facilitator molecule is produced in the membrane that serves as a gateway for the material. The material can now cross through the gateway spontaneously whenever a concentration gradient exists. Active transport: Flow up-hill against a concentration gradient; requires energy expenditure to keep going. The required energy is almost always provided directly by ATP. The ATP donates a phosphate to a specific gateway molecule which then “pumps” the desired molecule across the membrane, even if it goes against a concentration gradient. The ATP energy is used to drive the pump.
- #13: Shows successive stages in the dispersal of red dye molecules after being dropped into water.
- #15: Note that the molecules to be transported (little balls) are in higher concentration outside the cell than inside the cell. The molecules are of a type that cannot get to the inside of the cell by going directly through the membrane. The protein channel provides a passage way for the molecules to follow the concentration gradient.
- #16: Osmosis is the passive movement of water across a differentially permeable membrane in response to solute concentration gradients, pressure gradients, or both. Special case of diffusion. Involves the diffusion of water across a membrane that has solutions of differing concentration on opposite sides of the membrane. The water moves more abundantly toward the side with the highest concentration of dissolved materials. The concentration of water is obviously lower on the side with the highest concentration of dissolved materials. So the water is simply diffusing from a higher concentration of water to a lower concentration of water. Example: Pure water on one side; sugar solution on other (ƒ5-5). Sugar molecules can’t cross, but crowd membrane pores on syrupy side. Water crosses faster toward sugar. Net movement of water ====> sugar solution There is a net increase in volume on the side that has the higher concentration of sugar. The side of the membrane with the lower concentration of sugar experiences a loss of volume. This persistent movement can result in a build up of pressure known as osmotic pressure.
- #18: Note that molecules of water are constantly moving in BOTH directions across the cell membrane. Water will move faster FROM a low concentration of WATER than it moves AWAY from it. Though water is moving in both directions, there is a net gain of water on the side that starts out with less water (more stuff dissolved in the water).
- #19: Note that the concentration of the molecules is higher outside the cell than inside, but that the molecules are moving out, against the gradient. This always requires energy, thus the term “active” transport.
- #20: Here are some special adaptations of endocytosis. Pinocytosis is when a vesicle forms around and then surrounds and engulfs the liquid from outside the cell. Phagocytosis is when the vesicle forms around a solid particle like in slide 29. Receptor-mediated Endocytosis uses special receptor molecules that; Bind to specific molecules outside the cell Aggregate together as more and more of the receptors bind target molecules Cause the membrane to warp inwards where they aggregate Eventually pinch off to form a “coated” vesicle.
- #25: This shows the steps in exocytosis. A vesicle on the inside of the cell contains a cell product destined for export. The membrane of the vesicle merges with the plasma membrane, and the contents of the vesicle are now outside the cell.