Plasma Membrane Structure and Function Chapter 7 Image from: http://www.biologie.uni-hamburg.de/b-online/ge22/03.gif Slide show modified from: http://www.explorebiology.com/pptap/2005/ http://facstaff.bloomu.edu/gdavis/links%20100.htm
MEMBRANE MODELS 1915: Scientists analyzed isolated red blood cell membranes, found them made up of proteins and lipids 10 years later: E. Gorter and F. Grendel reasoned membranes are made of a phospholipid bilayer 1935: Hugh Davson and James Danielli proposed membrane was a sandwich of proteins and phospholipid bilayer with proteins on outside of phopholipids DAVSON-DANIELLI MODEL
FLUID MOSAIC MODEL Animation from: http://www.sp.uconn.edu/~terry/images/anim/fluidmem.gif Click here to See Fluidity Click here to See FLUIDITY 1972- S.J. Singer and G. Nicolson propose membrane is a mosaic of proteins and phospholipids that are constantly moving and changing
More than just a barrier Expanding our view of cell membrane beyond just a phospholipid bilayer barrier phospholipids plus
A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
Membrane Proteins Proteins determine most of membrane s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: peripheral proteins = loosely bound to surface of membrane integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein
Membrane Carbohydrates Attached to proteins (glycoproteins) or lipids (glycolipids) Play a key role in cell-cell recognition ability of a cell to distinguish neighboring cells from another important in organ & tissue development basis for rejection of foreign cells by immune system http://faculty.southwest.tn.edu/rburkett/gb1-osmosis.htm
Membranes provide a variety of cell functions
Molecules need to move across membranes in cells OUT waste ammonia salts CO 2 H 2 O products IN food carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O Image modiified from: http://www.accessexcellence.org/ab/gg/importprot.html
Cell Membranes are made of PHOSPHOLIPIDS & PROTEINS Amphipathic Molecules with both hydrophilic and hydrophobic regions phosphate hydrophilic lipid hydrophobic
HYDROPHILIC/HYDROPHOBIC areas determine positions of molecules in cell membranes hydrophobic amino acids stick in the lipid membrane anchors the protein in membrane hydrophilic amino acids stick out in the watery fluid in or out of cell
Semi-permeable membrane Need to allow passage through the membrane But need to control what gets in or out membrane needs to be semi-permeable sugar aa lipid H 2 O salt NH 3 So what makes a membrane semi permeable? See a movie
PHOBIC TAILS in center determine what can pass through
What molecules can get through directly? Small non-polar molar molecules (O 2 & CO 2 ) and hydrophobic molecules (fats & other lipids) can slip directly through the phospholipid cell membrane, but inside cell lipid O 2 NH 3 salt What about other stuff? outside cell sugar aa H 2 O
Diffusion 2nd Law of Thermodynamics governs biological systems Universe tends towards disorder Animatioin from: http://www.biologycorner.com/resources/diffusion-animated.gif Diffusion movement from [higher] [lower] concentration
Diffusion will also happen across a cell membrane as long as there is a difference in concentration and the membrane will let the molecule pass through.
Example: DIFFUSION IN CELLS http://facstaff.bloomu.edu/gdavis/links%20100.htm O 2 automatically moves from HIGHER concentration (in lungs) to LOWER concentration (in blood) CO 2 automatically moves from HIGHER concentration (in blood) to LOWER concentration (in lungs) http://www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.html
Diffusion of 2 solutes Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances
What if cell needs to move a molecule AGAINST the CONCENTRATION GRADIENT? (LOWER HIGHER) Cell example: Want to put MORE glucose into mitochondria when there is already glucose in there Image from: http://www.biologyclass.net/mitochondria.jpg
What if a cell needs to move LARGE or POLAR molecules that can t get through the membrane? http://www.d.umn.edu/~sdowning/membranes/membraneimages/jpegimages/diffusionmedium.jpg
What if cell needs to move molecules really? FAST (can t wait for it to diffuse) Cell example: Movement of Na + & K + ions required to send nerve signals http://www.steve.gb.com/images/science/neuron.png
Cells need a WAY to HELP molecules across cell membranes that can t go across by themselves
Kidspiration by: Riedell
Facilitated diffusion Move from HIGH to LOW concentration with aid of membrane transport proteins passive transport no energy needed facilitated = with help
Facilitated Diffusion Animation from: http://bio.winona.edu/berg/animtns/facdifan.gif Carrier Proteins Grab molecule, undergo conformational change, flip to other side Channel Proteins Create passageway for substances to pass through May be gated or not: open in response to chemical or electrical signals Animation from: http://www2.uic.edu/~myilma1/ionchannel.gif
Gated channels open only in presence of stimulus (signal) stimulus usually different from transported molecule ex: ion-gated channels when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na + ions to enter nerve cell ex: voltage-gated channels change in electrical charge across nerve cell membrane opens Na + & K + channels
Carriers and Channels are specific inside cell H 2 O aa sugar NH 3 salt outside cell... BUT STILL MOVES FROM [HIGHER] to [LOWER]
Active transport Uses energy from ATP to move molecules against concentration gradient Moves from [lower] [higher] Uses protein pumps OR vesicles Animations from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif
Moves Protons (H + ) across membrane PROTON PUMP EXAMPLES: - Creates acidic condition inside lysosomes - Photosynthesis/respiration use H + gradients to generate ATP See a movie proton pump
Active transport SODIUM-POTASSIUM PUMP Sets up difference in charge across membranes Pumps 3 Na + out and 2 K + in Makes cells more + outside more - inside See a movie about Na+ - K+ pump Animation from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif
All cells have voltages across their membranes = membrane potential Cytoplasm inside cell is more negative than extracellular fluid outside TWO FORCES drive diffusion Concentration gradient Electrical force Ions move DOWN the electrochemical gradient Favors the passage of cations (+) into cells
MEMBRANE POTENTIAL created by electrogenic pumps (proteins that generate voltage by pumping ions) PROTON PUMP Main electrogenic pump in plants, fungi, and bacteria Na + - K + PUMP Main electrogenic pump in animal cells http://fig.cox.miami.edu/~cmallery/150/memb/electrogenic.jpg Animation from: http://www.lionden.com/cell_animations.htm
Electrogenic pumps can be coupled to actively transport other substances = COTRANSPORT Ex: Cells pump H + out of cell then use the diffusion of H + back into cell down its gradient to drive the uptake of sucrose into cells http://faculty.southwest.tn.edu/rburkett/gb1-os29.jpg
Na + - K + pump sets up MEMBRANE POTENTIAL http://hyperphysics.phy-astr.gsu.edu/hbase/biology/nervecell.html#c2
ACTIVE transport Requires energy (ATP) Uses vesicles BULK TRANSPORT Watch two video clips about endo/exocytosis endo/exocytosis Animation from: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobooktransp.html
Endocytosis phagocytosis Cell eating large molecules; whole cells pinocytosis Cell drinking Fluids; Small molecules receptor-mediated endocytosis triggered by ligand signal
PHAGOCYTOSIS Animation from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html Cell eating takes in large molecules; whole cells See phagocytosis in action: http://www.accs.net/users/kriel/chapter%20nine/
Example in cells: WHITE BLOOD CELL ENGULFING BACTERIA using Phagocytosis SEE PHAGOCYTOSIS MOVIE http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg
PINOCYTOSIS Cell drinking Takes in fluids; Small molecules http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html
Receptor-mediated Endocytosis Ligand-any molecule that binds to a receptor site Binding of ligands allows uptake of specific molecules
Receptor-mediated Endocytosis Example in cells: Cholesterol Uptake Low density lipid proteins (LDL s) bind cholesterol and carry it in blood LDL s act as ligands binding receptors on cell surface and cholesterol is taken into cell http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rectpr.htm
EXOCYTOSIS Active transport (requires ATP) Uses vesicles Releases substances to outside INSULIN being released by pancreas cells using exocytosis
Video: http://www.southtexascollege.edu/tdehne/bc_shockwaveanimations/07swf-tourofthecell/07-16-endomembranesystem.swf GOLGI BODIES USE EXOCYTOSIS Animation from: http://www.franklincollege.edu/bioweb/a&pfiles/week04.html See a Golgi movie
http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x26.jpg
Transport summary
The Special Case of Water Movement of water across the cell membrane = OSMOSIS
Osmosis is diffusion of water Water is very important, so we talk about water separately Diffusion of water from high concentration of water to low concentration of water across a semi-permeable membrane Passive Uses no energy
Aquaporins 1991 2003 Transport proteins that move water rapidly into & out of cells evidence that there were water channels Peter Agre John Hopkins Roderick MacKinnon Rockefeller
TONICITY- ability of a solution to cause a cell to lose or gain water Refers to the concentration of SOLUTES Is a RELATIVE term, comparing two different solutions Solute-substance that is dissolved Solvent- substance solute in dissolved in Solution = solute + solvent
What if there is a difference in concentration but solute molecules can t move across a membrane? WATER will move until concentrations reach equilibrium
Animation: http://www.ouhscphysio.org/humanphys/animations/osmosis1.swf See an animation Osmosis1 http://faculty.etsu.edu/currie/images/osmosis1.jpg Animation
Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water hypotonic hypertonic net movement of water
Solute concentration Lower outside than inside Equal outside and inside Greater outside than inside HYPOTONIC ISOTONIC HYPERTONIC What will happen to an animal cell placed in different solutions?
Animation from: http://www.ouhscphysio.org/humanphys/animations/osmosis3.swf OSMOSIS HYPOTONIC: Concentration outside cell is inside the cell LESS THAN See an animation Osmosis3 Video More water enters than leaves cell so cell will swell and possibly burst Choose Blood Hypotonic link
Animation from: http://www.ouhscphysio.org/humanphys/animations/osmosis4.swf OSMOSIS See an animation OSMOSIS 4 HYPERTONIC: Concentration outside cell is inside cell GREATER THAN More water leaves cell than enters so cell shrinks Video Choose Blood Hypertonic link
Remember: Cells try to maintain stable internal conditions = HOMEOSTASIS http://bioweb.wku.edu/courses/biol121/osmosis/osmosis.asp So an animal cell in ISOTONIC conditions stays same size Water entering = water leaving Video Choose Blood Isotonic link
Animal cells = CYTOLYSIS = CRENATION http://www.stchs.org/science/courses/sbioa/metenergy/bloodcells.gif
http://www.stchs.org/science/courses/sbioa/metenergy/aplantturgor.gif Plant cells Cell wall keeps plant cell from bursting = PLASMOLYSIS
Managing water balance Isotonic animal cell immersed in isotonic solution blood cells in blood no net movement of water across plasma membrane water flows across membrane, at same rate in both directions volume of cell is stable
Osmosis.05 M.03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell
http://www.biology4kids.com/files/cell_vacuole.html Loss of water from central vacuole= plants wilt Vacuole full of water gives plant support (turgor pressure) Turgid = very firm Flaccid = limp
HYPOTONIC Sitting in the bathtub makes your fingers plump up and get pruny Grocery stores spray water on their veggies to plump them up
If cells can t maintain stable internal conditions... damage can result and cells can die. http://www.the-aps.org/education/lot/cell/quiz.htm
Cell survival depends on balancing water uptake & loss = OSMOREGULATION http://www.microscopy-uk.org.uk/mag/imgjun99/vidjun1.gif Paramecium vs. pond water Paramecium is hypertonic H 2 O continually enters cell to solve problem, specialized organelle, contractile vacuole
Drink salt water ACTIVELY pump ions OUT; Urinate less frequently Gills ACTIVELY pump ions in; Urinate frequently