2Biological membranesComplex, dynamic structures made of lipid and protein moleculesPerform many functionsDefine cell as a compartmentRegulate passage of materialsParticipate in chemical reactionsTransmit signals between cell interior and the environmentAct as part of energy transfer and storage
3Biological membranesPhysically separate cell interior from extracellular environmentForm compartments within eukaryotic cellsPlasma membraneRegulates passage of materialsParticipates in biochemical reactionsReceives information about environmentCommunicates with other cells
4Fluid mosaic modelMembranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteinsPhospholipid molecules are amphipathic and containHydrophobic regions which are repelled by waterHydrophilic regions which are attracted to water
9Membrane 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 membranes
11Proteins are embedded in the bilayer Integral membrane proteinsEmbedded in the bilayerTransmembrane proteinsIntegral proteins that extend completely through the membranePeripheral member proteinsAssociated with the surface of the bilayer
12Asymmetrically positioned to bilayer Membrane proteins, lipids, and carbohydratesAsymmetrically positioned to bilayerSides have different composition and structureFunction of member proteinsTransport of materialsActing as enzymes or receptorsCell recognitionStructurally linking cells
15Membranes are selectively permeable (only some materials are allowed in and out) Physical processesOsmosisDiffusionCarrier-mediated processesChannel proteinsCarrier proteins
16Diffusion: the movement of molecules from a region of higher concentration to one of lower concentration.
17Rate of diffusion depends on: Temperature (higher temperature, more movement of molecules)Size of molecules (smaller molecules tend to diffuse faster)Electrical charge (like charges repel and opposites attract)Difference in concentration (concentration gradient)
18Some molecules easily diffuse through the membrane WaterGasesSmall polar moleculesLarge, lipid soluble molecules
19OsmosisThe diffusion of water across a selectively permeable membrane from a region where there is a greater concentration of water to a region where there is less water.Osmotic pressure: the tendency of water to move into a solution.
21Osmotic pressure Concentration of dissolved substances in a solution Isotonic: equal solute concentrationHypertonic: solution has a greater concentration of solutes than the cell, loses water in plasmolysisPlasmolysis (collapse of a cell due to loss of water.Hypotonic: solution has a lesser concentration of solutes than the cell, gains water and swells
25Movement of particles through proteins If substances cannot pass through the lipid bilayer, they may still move through the membrane via protein channels.This may or may not require energy from the cell.Passive transport: no energy expenditureActive transport: energy expended by the cell.
26Facilitated diffusion does not require energy Occurs down a concentration gradientActive transport requires energyMoves ions or molecules against a concentration gradientCotransport requires energyATP-powered pump maintains a concentration gradient
29Cells expend metabolic energy to carry on physiological processes Exocytosis: large molecules leave the cell through fusion with the membraneEndocytosis: large molecules enter the cell through fusion with the membranePhagocytosisPinocytosisReceptor-mediated endocytosis
36Cells communicate by cell signaling Signaling molecules include NeurotransmittersHormonesRegulatory molecules
37Cell signaling involves Synthesis and release of signaling moleculeTransport to target cellsReception by target cells involving special surface receptors where the signaling protein docks.Signal transduction cells convert an extracellular into an intracellular one.Response by the cell: interior of the membrane protein undergoes a change in conformation, which activates proteins in the cytoplasm—often in a chain reaction.Termination of signal
39Cells in close contact often develop intercellular junctions Anchoring junctions connect epithelial cellsDesmosomes composed of filaments which hold cells subject to mechanical stresses together (in animal cells)Adhering junctions cement cells together with proteinsTight junctions seal off intercellular spaces in some animal cells. Seals are protein links.
40Gap junctions: permit transfer of small molecules and ions Gap junctions: permit transfer of small molecules and ions. These contain pores that connect cells. Allow rapid chemical and electrical communication between cells.Plasmodesmata: allow movement of certain molecules and ions between plant cells. Plasma membranes are continuous though the gaps.