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Topic - Membranes

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Cell Membranes are made of PHOSPHOLIPIDS & PROTEINS Amphipathic Molecules with both hydrophilic and hydrophobic regions phosphate lipid hydrophilic hydrophobic

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FLUID MOSAIC MODEL 1972- S.J. Singer and G. Nicolson propose membrane is a mosaic of proteins and phospholipids that are constantly moving and changing Click here to See Fluidity Animation from: http://www.sp.uconn.edu/~terry/images/anim/fluidmem.gif Click here to See FLUIDITY

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More than just a barrier Expanding our view of cell membrane beyond just a phospholipid bilayer barrier phospholipids plus

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2.4.2 Cell Membrane Micrograph

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A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

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2.4.1 Structures in Cell Membrane (animation)

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Membrane Proteins Proteins determine most of membranes specific functions enzymes, receptors and transport Membrane proteins: peripheral proteins = loosely bound to surface of membrane integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein

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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

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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

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Glycocalyx Fuzzy, sticky carbohydrate rich substance at the cell surface. aid in cell communication gives support to cell

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Cell Junctions Most cells live in tight knit communities (but some are Footloose) 3 factors act to bind cells together Glycoproteins in glycocalyx Contours fit together in tongue-and-groove fashion Special cell junctions

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Tight Junctions Series of proteins in cellular membrane which fuse together Impermeable junctions nothing can pass between the cells

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Desmosomes Anchoring junction connections between cells that prevent cells from separating.

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Gap Junctions Communicating junction between cells. Adjacent plasma membranes are very close and the cells are connected by hollow cylinders

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Membranes provide a variety of cell functions

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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 aa H2OH2O sugarlipidsalt NH 3 So what makes a membrane semi permeable? See a movie

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PHOBIC TAILS in center determine what can pass through

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Molecules need to move across membranes in cells Image modiified from: http://www.accessexcellence.org/AB/GG/importProt.html IN food carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O OUT waste ammonia salts CO 2 H 2 O products

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What molecules can get through directly? inside cell outside cell Small non-polar molar molecules (O 2 & CO 2 ) and hydrophobic molecules (fats & other lipids) can slip directly through the phospholipid cell membrane, but lipid salt aa H2OH2O sugar NH 3 O2O2 What about other stuff?

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2.4.4 Diffusion Diffusion is the passive movement of particles form a region of high concentration to a region of low concentration Molecules of dye Membrane (cross section) Net diffusion Equilibrium Net diffusion Equilibrium

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http://www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.html Example: DIFFUSION IN CELLS 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://facstaff.bloomu.edu/gdavis/links%20100.htm

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2.4.4 Osmosis is the passive movement of water molecules across a permeable membrane from lower solute to higher solute concentration Hypotonic = lower [solute] Hypertonic = higher [solute] Isotonic = equal [solute] Hypo -> Hypertonic Osmosis

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Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar Selectively permeable mem- brane: sugar mole- cules cannot pass through pores, but water molecules can More free water molecules (higher concentration) Water molecules cluster around sugar molecules Fewer free water molecules (lower concentration) Water moves from an area of higher free water concentration to an area of lower free water concentration Osmosis 2.4.4

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Animal cells http://www.stchs.org/science/courses/sbioa/metenergy/bloodcells.gif = CYTOLYSIS= CRENATION

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2.4.5 Simple diffusion is the tendency of molecules of a substance to spread out evenly in an available space. Substances diffuse down their gradient (high to low concentration). Small, non-ionic, non-polar particles are able to pass through the phospholipids is the membrane is permeable to them.

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Facilitated diffusion Move from HIGH to LOW concentration with aid of membrane transport proteins passive transport no energy needed facilitated = with help

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2.4.5 Facilitated diffusion is the movement of molecules across a membrane with the aid of channel proteins. Channel proteins create a bridge for particles to cross between the membrane. Their size and chemical properties makes them specific to one molecule.

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Carriers and Channels are specific inside cell outside cell sugaraa H2OH2O salt NH 3... BUT STILL MOVES FROM [HIGHER] to [LOWER]

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What if cell needs to move a molecule _________ the CONCENTRATION GRADIENT? _______________ Cell example: Want to put MORE glucose into mitochondria when there is already glucose in there (LOWER HIGHER) Image from: http://www.biologyclass.net/mitochondria.jpg AGAINST

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What if a cell needs to move _____ or ______ molecules that cant get through the membrane? http://www.d.umn.edu/~sdowning/Membranes/membraneImages/jpegimages/diffusionmedium.jpg LARGEPOLAR

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What if cell needs to move molecules really _______? (cant 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 FAST

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Cells need a ____ to ____ molecules across cell membranes that _______ across by ___________ WAY HELP cant go themselves

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2.4.6 Active transport involves moving substances AGAINST their concentration gradients (from low to high concentration). This is done by protein pumps embedded in the membrane. In contrast to passive transport, active transport requires energy in the form of ATP.

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2.4.6 Active Transport with ATP

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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 Animation from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif See a movie See a movie about Na+ - K+ pump

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2.4.6

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2.4.7 Vesicles can be to used to transport materials within the cytoplasm of the cell without mixing their components. They are small sacs of membrane that can change shape and move in and out of the cell Made in the rough Endoplasmic Reticulum by pinching off small regions of membrane ATP supplies energy

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2.4.7 Transmembrane glycoproteins Secretory protein Glycolipid Golgi apparatus Vesicle Transmembrane glycoprotein Membrane glycolipid Plasma membrane: Cytoplasmic face Extracellular face Secreted protein 4 1 2 3 Their membranes are made by the rough Endoplasmic Reticulum, which later merge with the plasma membrane via fusion. Membrane carbohydrates / lipids that are synthesized in the rER are modified in the Golgi apparatus

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2.4.7 Important Steps for Vesicles 1.Move material around in cell 2. Protein is synthesized by ribosomes on the rER 3. Protein is stored in the cisternae of the rER 4. Vesicles bud off cisternae and carry protein to the golgi apparatus

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2.4.7 Important Steps for Vesicles 5. Protein is processed in golgi apparatus 6. Protein is released in more vesicles and moved to the plasma membrane 7. Vesicle fuses with membrane 8. Protein is released

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2.4.8 Phospholipids in the plasma membrane are able to move within the bilayer, which results in its fluidity. This fluidity allows proteins embedded in the cell surface to float around and between plasma membranes Lateral movement (~10 7 times per second) Flip-flop (~ once per month)

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2.4.8 Membrane Fluidity

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2.4.8 Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. In exocytosis, transport vesicles migrate to the plasma membrane, fuse with it, and release their contents In endocytosis, the cell takes in macromolecules by forming new vesicles from the plasma membrane

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2.4.8 Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. In exocytosis, transport vesicles migrate to the plasma membrane, fuse with it, and release their contents In endocytosis, the cell takes in macromolecules by forming new vesicles from the plasma membrane

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2.4.8

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Example in cells: WHITE BLOOD CELL ENGULFING BACTERIA using Phagocytosis SEE PHAGOCYTOSIS MOVIE http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg

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EXOCYTOSIS Active transport (requires ATP) Uses vesicles Releases substances to outside INSULIN being released by pancreas cells using exocytosis

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http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x26.jpg

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Transport summary

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2.4.8 http://programs.northlandcollege.edu/biology/Bi ology1111/animations/active1.swf http://programs.northlandcollege.edu/biology/bio logy1111/animations/passive1.swf Passive Transport Active Transport