Bmsc Membranes

  1. Membrane Function
    • -seperate cells from environment to create defined intracellular space
    • -allow selective transport in/out of cell
    • -provide location for specialized pathways and processes (energy creation in mitochondria)
    • -nervous system communication through changes in electrical potential across membranes
    • -surface for receptors that read physiological signs and facilitate change from them
    • -mediate cell-cell recognition and interaction
  2. Membrane Structure
    • -impermeable to charged and polar molecules
    • -5 to 8 nm thick (different thicknesses at different parts of membrane)
    • -asymetrical(different on each face)
    • -fluid and dynamic
  3. Membrane Composition
    • -primarily lipid(phospholipids, glycoshingolipids and sterols) and protein
    • -more protein in membrane the more active it is
    • -outer and inner faces can have different composition, this serves different purposes (nothing happens by accident kinda thing)
  4. Peripheral Membrane Proteins
    • -associate with membrane through charge-charge interactions or H bonding
    • -weakest link to membrane, can easily be removed by change in temp or pH
  5. Integral Membrane Proteins
    • -span through the entire bilayer
    • -can be extracted from membrane with detergents (dish soap)
    • -protein direction matters
    • -transmembrane portion hydrophobic, extra and inter cellular portions hydrophyllic
  6. Types of Trans-Membrane (integral) Proteins
    • -Beta barrel and alpha helical bundles
    • -alpha helical bundles almost always have 7 alpha helices
    • -alpha helices H bond with each other amide-carbonyl to satisfy bonding arrangements
    • -inter membrane portion structure can be predicted by AA sequence
    • -stretches of 20 hydrophobic residues (AA) are likely membrane spanning
  7. Greasy Fingers
    • -proteins that are anchored to the membrane through lipid attachment that serve as anchors, this allows for them to be easily removed by a lipase
    • -GPI anchored proteins always at outer face
    • -fatty acyl or prenylated proteins always to innner face
  8. Membrane Fluid Mosaic
    • -lateral movement of protein and lipids is very rapid and constant
    • -temperature can affect membrane fluidity
    • -too cold=ordered paracrystalline gel state
    • -too hot=liquid disordered state
    • -ideal temp=liquid ordered state
    • -cells can adjust membrane composition to maintain liquid ordered state
  9. Transbilayer Movement
    • -flipping from facing out, to facing in or vice versa
    • -requires catalyst, flippase
    • -slow process because polar head group must pass through hydrophobic trans membrane environment
    • -membrane lipids are initially produced on inner face and some must be flipped to outer face
  10. Lateral Membrane Movement 
    • -higher order structures can be "fenced" withing membrane, restricting movement
    • -membrane proteins can also be linked to internal structures, which again limits lateral movement
  11. Membrane Rafts
    • -glycosphingolipids form clusters (rafts) that exclude glycerophospholipids
    • -longer, saturated acyl groups of sphingolipids form better associations with cholesterol in outer layer which allows thicker and more ordered rafts
  12. Membrane Fusion
    • -easily and frequently occurs because they are non covalent bonds
    • Generally Involves
    • 1)appropriate recognition
    • 2)close association of membrane surfaces, with exclusion of water molecules
    • 3)localized disruption of the membranes to allow fusion of outer leaflets (hemifusion)
    • 4)fusion of bilayers to form single bilayer
    • 5)regulation 
  13. Botox and Botulism
    • -botulism found in canned foods and improperly handled meats
    • -botulinic toxin cleaves SNARE and SNAP25 proteins which are neurotransmitter proteins, this causes paralysis and eventually death
    • -botox is a localized injection to cleave the proteins for both muscle spasms and cosmetic applications
  14. Simple Diffusion
    • -non polar gases (Oand CO2) and hydrophobic molecules can directly cross the membrane when moving down the concentration gradient
    • -no energy needed, does not require carrier protein and not saturable
  15. Facilitated Diffusion
    • -uses membrane transporters to lower the activation energy barrier for crossing the membrane
    • -no energy needed
    • -two kinds, channels and carriers
  16. Facilitated Diffusion Channels
    • -can only transport molecules down the concentration gradient
    • -molecules move through very quickly (door analogy) because channels bind substrate very weakly
    • -cannot be saturated 
    • -allow movement of polar molecules by lining the interior of the channel with other polar molecules
    • -molecules must have appropriate size, charge and geometry to use
  17. Facilitated Diffusion Carriers
    • -protein binds specific solute (molecule) and transports it down concentration gradient
    • -does not require energy
    • -can become saturated becaue it moves slowly (turnstile vs door)
    • -occurs with glucose permease of erythrocytes, facilitated diffusion occurs 50,000 times faster than regular diffusion, specific for movement of D-glucose
  18. Coupled Transport
    • -electroneutral exchange of ions prevents the electrical potential across the membrane from changing
    • -chloride bicarbonate exchange protein
  19. Active Transport
    • -uses the input of energy(ATP) to move molecules against their concentration gradient
    • -ATP is used to force a conformational change in the transport/carrier protein that favors the movement of the molecule against the gradient
    • -can become saturated
  20. F-Type ATPase
    -uses a proton gradient in reverse to generate ATP in mitochondria and chloroplasts
  21. V-Type ATPase
    -pumps protons across a membrane to acidify the contents of cell
  22. ABC Transporters
    • -active transport
    • -pump things out of the cell
    • -multi drug transporter pumps can cause medicine to be ineffective because the body is so good at expelling unknown substances
    • -contain two ATP binding domains
    • -ATP-Binding Cassette transporters
  23. Secondary Active Transport
    • -uses the energy created by moving molecules down their concentration gradient as power to move other molcules up their own concentration gradient
    • -ex. glucose uptake-glucose can move against its gradient by paying the price of moving 2 Na ions down their concentration and electrical gradient (implication being that no Na ions to move means no glucose can be moved either)
    • -requires carriers, can be saturated
  24. Voltage Gated Ion Selective Channels
    • different from ion transporters 3 ways
    • -much faster
    • -no saturation limits
    • -gated (can be opened and closed in response to cellular events)
    • -carbonyls of alpha helices line up facing the inside of channel which allows them to take the place of water for H bonding
    • -channels are narrow and very specific K+ channels allow K+ to move through 10,000 times faster than a Na+ ion
Card Set
Bmsc Membranes
Chapter 11 Membranes