The Body in Motion

Biological Membranes1Biological membranesComplex, dynamic structures made of lipid and protein moleculesPerform many functionsDefine cell as a compartmentRegulate passage of materials (helps to maintain homeostasis)Participate in chemical reactionsTransmit signals between cell interior and the environmentCommunicates with other cellsAct as part of energy transfer and storage2Cell MembraneThe cell membrane is flexible and allows a unicellular organism to move

copyright cmassengale3The Plasma Membrane9/8/2011G. Podgorski, Biol. 10103The Cell MembraneAll cells are separated from the external environment by a Plasma Membrane Key Feature:Semipermiable (only allowing certain materials in/out of cells.) It is composed of many components. Phospholipids Very similar to triglycerides however, one of the fatty acid chains has been replaced by a very polar Phosphate group Cholesterol Provides stabilityProteinsHelps to transport materials across the membrane

4Phospholipids & WaterThe polar end is attracted to water, non polar tails are repelled by it. This forces the phospholipids to take an arrangement such that their tails face each other. This accomplishes 2 things. The polar heads can be adjacent to polar water molecules The non-polar tails can be adjacent to each other.

56Phospholipids

Contains 2 fatty acid chains that are nonpolarHead is polar & contains a PO4 group & glycerolcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10106Phospholipids form bilayers in water

Phospholipids in waterDetergent in water7Fluid mosaic modelMembranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteinsPhospholipid molecules are amphipathic and containHydrophobic regionsHydrophilic regions89FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like its a liquid.MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

FLUID MOSAIC MODELcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 1010910

Cell MembraneHydrophobic molecules pass easily; hydrophilic DO NOTcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10101011Small molecules and larger hydrophobic molecules move through easily.e.g. O2, CO2, H2O

Semipermeable Membranecopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10101112

Ions, hydrophilic molecules larger than water, and large molecules, such as proteins, do not move through the membrane on their own. Semipermeable Membranecopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101012Plasma membrane of mammalian red blood cell

13Membrane propertiesOrderly arrangement of phospholipid molecules make the cell membrane a liquid crystalAllow molecules to move rapidlyProteins move within membraneLipid bilayers areFlexibleSelf-sealingCan fuse with other membranes14Membrane ComponentsThe membrane requires a few more components to make it complete: Cholesterol Functions to hold the membrane together like glue. Adds strength to the membrane. Prevents tails from bunching togetherProteins (2 types) defined by how tightly they are associated with the membraneIntegral Proteins Extend into or through lipid bilayer Often are channel proteins allowing large molecules in/outPeripheral membrane Proteins Exist only on surfaces of the bilayer Often serve as receptor molecules Glycoproteins serve as cellular markers (nametags)

15Detailed structure of the plasma membrane

16Integral membrane proteinsEmbedded in the bilayerTransmembrane proteinsIntegral proteins that extend completely through the membranePeripheral member proteinsAssociated with the surface of the bilayer1718

Proteins Are Critical to Membrane Function

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101018Membrane proteins, lipids, and carbohydratesAsymmetrically positioned to bilayerSides have different composition and structureFunction of member proteinsTransport of materialsActing as enzymes or receptorsCell recognitionStructurally linking cells19Asymmetry of the plasma membrane

Freeze-fracture method: the membrane splits along the hydrophobic interior of the lipid bilayer. Enables scientist to observe numerous particles on the fracture faces.Influenced the development of the Fluid Mosaic Model 20Membranes are selectively permeablePhysical processesOsmosisDiffusionCarrier-mediated processesChannel proteinsCarrier proteins

2122Types of Transport Across Cell Membranes

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101022Concentration GradientThe difference in concentration of a substance from one point to another

*transport is often referred to as moving either against or down the concentration gradient24Simple DiffusionRequires NO energyMolecules move from area of HIGH to LOW concentration

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10102425DIFFUSIONDiffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101025DiffusionWhat influences the rate of diffusion?TemperaturePressureElectrical currents Molecular sizeDiffusion: net movement of a substance from a region of greater to lower concentration

2728Diffusion of Liquids

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10102829Diffusion through a Membrane

Cell membraneSolute moves DOWN concentration gradient (HIGH to LOW)The Plasma Membrane9/8/2011G. Podgorski, Biol. 101029Osmosis: water passes throughselectively permeable membranefrom region of higherconcentrationto lower

3031OsmosisDiffusion of water across a membraneMoves from HIGH water potential (low solute) to LOW water potential (high solute)

Diffusion across a membraneSemipermeable membranecopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10103132Diffusion of H2O Across A Membrane

High H2O potentialLow solute concentrationLow H2O potentialHigh solute concentrationcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101032Osmotic pressureThe pressure that must be exerted on the side of a selectively permeable membrane containing the higher solute concentration to prevent the diffusion of water from the side containing the lower solute concentrationInfluenced by the concentration of dissolved substances in a solutionTurgor pressureInternal hydrostatic pressure in walled cells (plants, fungi, algae and bacteria)

3334Cell in Isotonic SolutionCELL10% NaCL90% H2O10% NaCL90% H2OWhat is the direction of water movement?**The cell is at dynamic equilibriumENVIRONMENTNO NET MOVEMENTThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10103435Cell in Hypotonic SolutionCELL10% NaCL90% H2O20% NaCL80% H2OWhat is the direction of water movement?The Plasma Membrane9/8/2011G. Podgorski, Biol. 10103536Cell in Hypertonic SolutionCELL15% NaCL85% H2O5% NaCL95% H2OWhat is the direction of water movement?ENVIRONMENTThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101036Responseof animalcells to osmotic pressure

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Isotonic SolutionNO NET MOVEMENT OF H2O (equal amounts entering & leaving)Hypotonic SolutionCYTOLYSISHypertonic SolutionPLASMOLYSIScopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101038What Happens to Blood Cells?copyright cmassengale39

Turgorpressureand plasmolysis

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Three Forms of Transport Across the Membrane

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104142

Passive TransportSimple Diffusion Doesnt require energy Moves high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104243Passive Transport

Facilitated diffusionDoesnt require energyUses transport proteins to move high to low concentrationOccurs down a concentration gradient

Examples: Glucose or amino acids moving from blood into a cell.copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104344Types of Transport ProteinsChannel proteins are embedded in the cell membrane & have a pore for materials to crossCarrier proteins can change shape to move material from one side of the membrane to the othercopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104445Facilitated Diffusion

Molecules will randomly move through the pores in Channel Proteins.copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104546Facilitated DiffusionSome Carrier proteins do not extend through the membrane.They bond and drag molecules through the lipid bilayer and release them on the opposite side.

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 10104647Carrier ProteinsOther carrier proteins change shape to move materials across the cell membrane

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101047Active transportMoves ions or molecules against a concentration gradientCotransportATP-powered pump maintains a concentration gradient4849

Sodium-Potassium Pump3 Na+ pumped out for every 2 K+ pumped in; creates a membrane potentialThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101049Sodium-potassiumpump

Requires energy or ATPMoves materials from LOW to HIGH concentrationAGAINST concentration gradient50Functions of membrane proteins

51Cells expend metabolic energy to carry on physiological processesExocytosisEndocytosisPhagocytosisPinocytosisReceptor-mediated endocytosis5253Moving the Big StuffMolecules are moved out of the cell by vesicles that fuse with the plasma membrane.Exocytosis- moving things out.This is how many hormones are secreted and how nerve cells communicate with one another.

The Plasma Membrane9/8/2011G. Podgorski, Biol. 10105354Exocytosis animation

Inside CellCell environmentcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101054Exocytosis

5556Endocytosis Phagocytosis

Used to engulf large particles such as food, bacteria, etc. into vesiclesCalled Cell Eatingcopyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101056copyright cmassengale57

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Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101058Phagocytosis

59Pinocytosis

6061PinocytosisCell forms an invaginationMaterials dissolve in water to be brought into cellCalled Cell Drinking

copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101061Receptor-mediated endocytosis

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Receptor-Mediated EndocytosisSome integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.copyright cmassengaleThe Plasma Membrane9/8/2011G. Podgorski, Biol. 101063Cells communicate by cell signalingSignaling molecules includeNeurotransmittersHormonesRegulatory molecules

64Cell signaling involvesSynthesis and release of signaling moleculeTransport to target cellsReception by target cellsSignal transductionResponse by the cellTermination of signal65Cells in close contact often develop intercellular junctionsAnchoring junctionsDesmosomesAdhering junctionsTight junctionsGap junctionsPlasmodesmata66Anchoring JunctionsDesmosomesPoints of attachmentAnchored to system of intermediate filaments inside the cells Adhering junctionsCement cells together

Ex: Epithelial cells

67Tight junctionsLiterally tight connections between membranes of adjacent cellsHelp to seal off body cavitiesEx: Form the blood-brain barrier to prevent substances in the blood from entering the brain

68Gap junctions

Bridge the space between cellsAct as communicating junctionsContain channels connecting the cytoplasm of adjacent cellsProvide for rapid chemical and electrical communicationex: Pancreatic cells, cardiac cells, nerve cells

69PlasmodesmataAllow materials and ions to pass between plant cellsConnect the cytoplasm of neighboring cellsMost contain desmotubles that run through the channel and connects the smooth ER of two adjacent cells

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