Plasma Membrane Structure and Function Chapter 8 Image

Plasma Membrane Structure and Function Chapter 8 Image from: http: //www. biologie. uni-hamburg. de/b-online/ge 22/03. gif Slide show modified from: http: //www. explorebiology. com/ppt. AP/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/GB 1 -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/import. Prot. 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 molecules (O 2 & CO 2) and hydrophobic molecules (fats & other lipids) can slip directly through the phospholipid cell membrane, but… inside cell NH 3 lipid O 2 outside cell sugar aa salt H 2 O What about other stuff?

Diffusion • 2 nd 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/case 2/2_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 AGAINST the molecule _____ 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 LARGE or ______ POLAR move _____ molecules that can’t get through the membrane? http: //www. d. umn. edu/~sdowning/Membranes/membrane. Images/jpegimages/diffusionmedium. jpg

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

WAY to Cells need a ____ 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: //www 2. uic. edu/~myilma 1/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/bio 4 fv/page/cell-movement. html http: //www. cat. cc. md. us/courses/bio 141/lecguide/unit 1/eustruct/images/sppump. gif

PROTON PUMP Moves Protons (H+) across membrane 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/bio 141/lecguide/unit 1/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 http: //fig. cox. miami. edu/~cmallery/150/memb/electrogenic. jpg Na+- K+ PUMP Main electrogenic pump in animal cells 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/GB 1 -os 29. jpg

Na+ - K+ pump sets up MEMBRANE POTENTIAL http: //hyperphysics. phy-astr. gsu. edu/hbase/biology/nervecell. html#c 2

BULK TRANSPORT • ACTIVE transport • Requires energy (ATP) • Uses vesicles Watch two video clips about endo/exocytosis Animation from: http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Bio. Booktransp. html

Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis “Cell eating” large molecules; whole cells “Cell drinking” Fluids; Small molecules triggered by ligand signal

PHAGOCYTOSIS Animation from: http: //academic. brooklyn. cuny. edu/biology/bio 4 fv/page/cell-movement. html “Cell eating” takes in large molecules; whole cells See phagocytosis in action: http: //www. accs. net/users/kriel/chapter%20 nine/

Example in cells: WHITE BLOOD CELL ENGULFING BACTERIA using Phagocytosis SEE PHAGOCYTOSIS MOVIE http: //fig. cox. miami. edu/~cmallery/255 ion/fig 14 x 28. 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/bio 4 fv/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_Shockwave. Animations/07 SWF-Tour. Of. The. Cell/07 -16 -Endomembrane. System. swf GOLGI BODIES USE EXOCYTOSIS Animation from: http: //www. franklincollege. edu/bioweb/A&Pfiles/week 04. html See a Golgi movie

http: //fig. cox. miami. edu/~cmallery/255 ion/fig 14 x 26. 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 water channels Peter Agre Roderick Mac. Kinnon John Hopkins 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/osmosis 1. swf See an animation Osmosis 1 http: //faculty. etsu. edu/currie/images/osmosis 1. 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 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/osmosis 3. swf OSMOSIS See an animation Osmosis 3 Video Choose Blood Hypotonic link HYPOTONIC: Concentration outside cell is LESS THAN ________ inside the cell More water enters than leaves cell so cell will __________ swell and possibly burst

Animation from: http: //www. ouhscphysio. org/humanphys/animations/osmosis 4. 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/biol 121/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. biology 4 kids. 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/imgjun 99/vidjun 1. 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