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Bio- Membrane function, <- refer to green, <- refer to green -…
Bio- Membrane function
Plasma membrane
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Components
Lipids
Proteins
- Integral (span the bilayer- fill the whole membrane) or peripheral (only on one side - usually cytoplasm side)
Cholesterol
- helps maintain the fluidity of the membrane
is selectively permeable
Allows the passage of certain molecules, while blocking others
- small, non-polar molecules naturally follow their concentration gradient
- no energy cost
High concentration -> Low concentration
Phospholipid Structure
Amphipathic
- water loving head group (hydrophilic)
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- phospholipids can move laterally in the membrane
Fluid Mosaic Model
- membranes are NOT rigid
- flexible, and lipids and proteins are always in flux
IMPORTANT?
- enables proteins to diffuse rapidly in plane of bilayer
- permits lipids and proteins to diffuse from site of synthesis to other areas
- allows membranes to fuse together and mix molecules
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Gas exchange in Lungs
- gas like O2 and CO2 can freely diffuse bc they are small & nonpolar
- O2 conc. is high in the alveoli in the capillaries, so it moves into the capillaries
Osmosis
- the diffusion of water across a semipermeable membrane
Tonicity
- the solute conc. of a solution compared to that of a cell
Isotonic
- solute and water concs. are equal on both sides of cellular mem.
- there is no net gain or loss of water by the cell
Hypotonic- conc. of solute is HIGHER inside the cell
- water will diffuse into cell (high -> low)
Hypertonic
- conc. of solute is higher in the solution then inside the cell
- water conc, is higher inside the cell
- diffuse out of cell (high -> low)
Facilitated Transport
- diffusion that requires a membrane protein
- high -> low
- No ATP required
Active Transport
- movement from low -> high
- carrier proteins and ATP are needed!
- ATP allows carrier pro. to bind the substance being transported
- carrier proteins = highly specific for their molecule
- usually called "pumps"
sodium - potassium pump
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- important in nerve/muscle cells
- "cotransport" of sodium ion (NA+) and potassium ions (K+)
- moves the ions from low -> high
- requires carrier protein & ATP
Bulk transport
- moves large molecules in and out of cell
- proteins, polysaccharides, nucleic acids, and foreign invaders
- Exocytosis = Exit out
- Endocytosis = Exit out
3 Methods of Endocy.
- phagocytosis (trans of large substances)
- pinocytosis (small substances)
- receptor- mediated (selective/ more efficient)
- uses vesicles to transport these large molecules
- costs ATP
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