Membrane Structures and Functions
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The document provides an overview of membrane structure and function: 1. It describes the fluid mosaic model of the plasma membrane, which explains that membranes are composed of a bilayer of phospholipids embedded with integral and peripheral proteins that give the membrane a fluid structure. 2. The key components of cell membranes are phospholipids, cholesterol, and integral and peripheral proteins. Transport proteins like channel and carrier proteins allow selective permeability across the membrane. 3. Membrane proteins have a variety of important roles including cell-cell recognition, transport, enzymatic activity, and attachment to intracellular structures. The fluid mosaic structure and selective permeability of membranes allows them to regulate cellular traffic.
Membrane Structures and Functions
- 2. Objective: Build a 3-D model of the plasma membrane and use it to describe: 1.The fluid mosaic model of the plasma membrane 2.The components of cell membranes
- 3. Membrane StructureMembrane Structure & Function& Function The selectively permeable plasma membrane acts as traffic control for the cell, allowing only certain things in at any given time
- 4. Today’s Objective Describe the structure and function of the plasma membrane Explain why we say it is a fluid mosaic Identify the primary roles of membrane proteins Explain why we say the membrane is selectively permeable
- 5. What is the membrane made of?
- 6. Cell Membranes are FluidCell Membranes are Fluid Mosaics of Lipids & ProteinsMosaics of Lipids & Proteins *Phospholipids are amphipathic- both hydrophobic & hydrophilic Bilayer of phospholipids
- 7. Cholesterol (a type of steroid – a lipid) helps with membrane fluidity
- 8. Membrane Proteins Integral proteins – span the entire width of the phospholipid bilayer Peripheral proteins – loosely bound to the surface of the membrane
- 9. Membrane Structure ResultsMembrane Structure Results in Selective Permeabilityin Selective Permeability The fluid mosaic model explains how membranes regulate cellular traffic --it explains how form fits function Fibers of extracellular matrix Cytoskeleton Cytoplasm Attachment to cytoskeleton and extracellular matrix Cell signaling Enzymatic activity Transport Intercellular joining Cell-cell recognition Cytoplasm
- 10. So…
- 11. How is the plasma membrane selectively permeable?
- 12. The Permeability of the Lipid Bilayer Small nonpolar (hydrophobic) molecules can pass freely across the membrane http://www.sumanasinc.com/webcontent/an imations/content/diffusion.html
- 13. need the help of transport proteins
- 14. Transport Proteins Transport proteins are just as selective as the lipid bilayer. Two types of transport proteins: 1. Channel Proteins- a hydrophilic tunnel through which hydrophilic molecules & ions can pass through 2. Carrier Proteins- Hold onto molecules and change shape in a way that shuttles them across the membrane What kind of molecules will the transport proteins help moved across the membrane? Why?
- 15. So… • Explain why we say the membrane is selectively permeable
- 16. The varied roles of membrane proteins
- 17. Various Membrane Protein Functions Cell-to-cell recognition Intercellular junctions (gap junctions, tight junctions) Receptor for a chemical signal Transport Enzymes Attachment to the cytoskeleton
- 18. Carbohydrates are important in cell-to-cell recognition Glycolipids – polysaccharide bonded to lipid Glycoproteins – polysaccharide bonded to protein
- 19. So… • Identify the primary roles of membrane proteins
- 20. Putting it all together Read the case study on cystic fibrosis and answer the accompanying questions.
- 22. Passive Transport is Diffusion of a Substance Across a Membrane With No Energy Requirement Molecules (above 0 K) are always in motion Diffusion is the tendency for molecules to move down their concentration gradient until a dynamic equilibrium is reached.
- 23. Osmosis Osmosis is the diffusion of water molecules from areas of high (free) water concentration to areas of lower concentration
- 24. Quick Think Oxygen & carbon dioxide can cross the lipid bilayer without help from membrane proteins. What properties allow this to occur? Water sometimes needs the help of a transport protein (aquaporins) to cross the membrane. Why?
- 25. = solute Water Balance of CellsWater Balance of Cells WithoutWithout Walls e.g.Walls e.g. There are 3 states of tonicity when comparing two solutions: 1. Isotonic: No net movement of water across the cell membrane Iso= equal Animal CellsAnimal Cells
- 26. =solute Water Balance of CellsWater Balance of Cells WithoutWithout Walls e.g. Animal CellsWalls e.g. Animal Cells There are 3 states of tonicity when comparing two solutions: 2. Hypertonic: A solution that is relatively hypertonic contains more non-penetrating solutes than the solution that it is being compared to Hyper = More
- 27. Water Balance of CellsWater Balance of Cells WithoutWithout Walls e.g. Animal CellsWalls e.g. Animal Cells There are 3 states of tonicity when comparing two solutions: 3. Hypotonic: A solution that is relatively hypotonic contains fewer non-penetrating solutes than the solution that it is being compared to Hypo = less =solute
- 28. Quick Think Where will water move and why? 1. A cell placed in a 10% salt solution (that’s very salty). 2. A cell placed in distilled water. 3. A cell placed in an isotonic solution. The inside of the cell is ________ compared to the outside of the cell because it has more/fewer/same solutes dissolved in solution so water will move _____________________
- 29. Water Balance of CellsWater Balance of Cells WithoutWithout Walls e.g. Animal CellsWalls e.g. Animal Cells Osmoregulation- The control of water balance within a cell. Various methods of osmoregulation are present in organisms that are specially adapted to living in hypertonic or hypotonic environments: Contractile Vacuole
- 30. Quick Think If a Paramecium were to swim from a hypotonic environment to an isotonic one, would the activity of its contractile vacuole increase or decrease? Why?
- 32. Water Balance of CellsWater Balance of Cells WithWith Walls e.g.Walls e.g. Plant CellsPlant Cells …Prokaryotes & Fungi Too! Hypotonic solutions, like rain, cause turgor (firmness) in plants because the cell wall pushes back against the intake of additional water after a certain point: Turgor= nice, healthy plant When plant cells are isotonic with their environment, they become flaccid
- 33. Water Balance of CellsWater Balance of Cells WithWith Walls e.g. PlantsWalls e.g. Plants In hypertonic solutions, cells with walls experience plasmolysis- they lose water to their environment until the cell membrane shrivels & pulls away from the cell wall. The result is a wilted & possibly dead plant (or other organism) = solute
- 34. Facilitated Diffusion: PassiveFacilitated Diffusion: Passive Transport Aided by ProteinsTransport Aided by Proteins Facilitated diffusion is the use of transport proteins, like channel & carrier proteins, to speed up the diffusion of molecules across a membrane. A specific type of channel proteins are ion channels which are often gated channels-the presence of a stimulus causes them to open/close Example- the presence of a certain neuro- transmitter, like acetylcholine, would cause the gated channels of a nerve cell to open and let Na+ into the cell
- 35. Quick Think List all the types of passive transport you can think of.
- 36. Conclusion Read the case studies and answer the corresponding questions
- 38. Active Transport Uses Energy to MoveActive Transport Uses Energy to Move SolutesSolutes AgainstAgainst Their GradientsTheir Gradients PassivePassive TransportTransport Includes osmosis, diffusion, & facilitated diffusion ActiveActive TransportTransport Molecules move down concentration gradient Molecules are moved against concentration gradient Doesn’t require energy Requires energy No help, channel proteins &/or carrier proteins Carrier proteins
- 39. Active TransportActive Transport ATP energy can power active transport by binding one of its phosphates to the transport protein
- 40. Maintenance of MembraneMaintenance of Membrane Potential by Ion PumpsPotential by Ion Pumps All cell membranes have a charge across them due to a difference in ion concentration on either side of the membrane This createThis create membrane potentialmembrane potential - higher- higher negativenegative ionion concentration inside the cell relative to the outside of the cellconcentration inside the cell relative to the outside of the cell ThisThis electrochemical gradientelectrochemical gradient can help move ions into the cellcan help move ions into the cell
- 41. Creating Membrane Potential-Creating Membrane Potential- Two ExamplesTwo Examples Ion pump=Sodium-Potassium Pump Proton Pump
- 42. Cotransport: Coupled TransportCotransport: Coupled Transport by a Membrane Proteinby a Membrane Protein Cotransport is when the action of one proton pump creates the electrochemical gradient to power another transport protein The natural flow of H ions back The natural flow of H ions back in sorta in sorta “sucks” in the other “sucks” in the other desired molecule desired molecule
- 43. Bulk TransportBulk Transport Across the PlasmaAcross the Plasma Membrane Occurs by Exocytosis &Membrane Occurs by Exocytosis & EndocytosisEndocytosis Exocytosis: Transport vesicles from golgi apparatus move to cell membrane. The vesicle membrane fuses with the cell Membrane, and the contents is expelled out of the cell
- 44. Endocytosis: A section of the plasma membrane sinks inward & pinches off to form a vesicle that transports materials into the cell; Three kinds: Phagocytosis: “Cell eating” Pseudopodia of the cell membrane “reach out” & engulf particles. These particles are then digested when a vacuole fuses with a lysosome Pinocytosis: “Cell drinking” Part of the cell membrane caves in and gulps extracellular fluid & the molecules dissolved in it Receptor-Mediated Endocytosis: Allows for the bulk transport of specific extracellular particles. The vesicle forms only when certain ligands bind to receptor proteins on the cell membrane.
- 45. Quick Think The carbohydrates attached to some of the proteins and lipids of the cell membrane are added as the membrane is made and refined in the ER and Golgi. The new membrane then forms transport vesicles that travel to the cell surface. On which side of the vesicle membrane are the carbohydrates?
- 46. http://www.wiley.com/college/pratt/0471393878/stude nt/animations/membrane_transport/index.html http://programs.northlandcollege.edu/biolog y/Biology1111/animations/transport1.html Websites to check outWebsites to check out
- 47. Quick Write What is the function of the plasma membrane and how does the structure of the plasma membrane help it with this job?