Transport Across Biological Membranes Flashcards
Selectively permeable membrane
Passage of only some molecule
Active or passive transport
Active: requires energy
Concentration gradient: diff in substance concentration in diff locations
Passive: high C to low C
Active: low C to high C (energy needed)
Passive Transport (low to high C until equilibrium)
Simple Diffusion: small, non polar molecules (interact w/ hydrophobic region of bilayer) - no proteins, just pass through
Ex: gases oxygen , CO2
Facilitated Diffusion: large, polar (not interact with hydrophobic regions) - proteins channels or carriers bind to molecule (revolving door)
Ex: ions (Cl-), glucose
Isotonic: C same on both sides
Hypertonic: high C
Hypotonic: low C
Channel Proteins (photo)
1) Carry ions across membrane
2) gated channels : open & close (response to chemical or electrical stimulus)
- specific to each ion (but special cases)
- C gradient, membrane potential, channel open?
Interior: hydrophilic/polar (ions pass)
Membrane potential
Difference in electrical potential (voltage) on both sides (among of ions/charge)
Inside cell: negative (DNA & proteins)
Transmission of nervous signals & muscle contraction, cellular processes, gated channels
Carrier proteins
Carrier changes shape to transport molecule (ions, amino acids, sugars, etc.)
Functioning: C gradients
Rate: number of carriers (physically bind to molecules)
Osmosis
1) Diffusion of water (facilitated diffusion)
2) Channel protein: aquaporin
3) high water C to low water C = hypotonic to hypertonic
Effects of osmosis (hydrostatic vs osmotic pressures)
Cell tries to balance hydrostatic (pressure or cytoplasm against membrane - cell on environ.) & Osmotic pressures (force to stop water from entering cell - pressure of environ. on cell)
Until equilibrium (water moves at similar rate)
Osmosis & cells
Animal cells:
Isotonic solution: normal cell
Hypotonic solution: cells swell & burst
Hypertonic solution: cells shrivel
Plants cells:
Isotonic solution: normal cell
Hypotonic solution: turgid cell (swell, but not burst, cuz cell wall maintains structure)
Hypertonic solution: cytoplasm shrinks from cell wall (cell wall remains, maintains external shape of cell)
Methods of maintains hydrostatic & osmotic pressures (3)
1) Extrusion (single celled): physically pump water out of cell
2) Isosmotic regulation: regulate levels of solutes outside of cell to match inside cell
3) Turgor pressure: cell wall in plants (hypertonic central vacuole: press membrane against cell wall)
Photo
Turgor pressure high: plants full
Turgor pressure low: plants wilt
Active transport (Phosphorylation)
Requires energy from hydrolysis of ATP
Phosphorylation (addition of phosphate group to molecules from ATP): change in protein shape (add 2-)
By kinases
Phosphate group removed by phosphatases
Active Transport (Carriers)
Carriers + Hydrolysis of ATP
Uniporters: 1 molecule, 1 direction
Coupled/co-transport: energy to move against C gradient
Symporters: 2 molecules, 1 direction
Antiporters: 2 molecules, 2 directions
Antiporter (coupled/co-transport)
Ex: Sodium-Potassium pump (photo)
1) Na+ in cytoplasm binds to pump (carrier)
2) simulates phosphorylation by ATP (active transport requires energy)
3) phosphorylation (add phosphate group to carrier) causes change in protein (add -2 charge from phosphate group), change in protein carrier shape, Na+ is expelled to outside cell
4) K+ outside cell binds to pump (carrier) - triggers release of phosphate group from carrier
5) protein original shape returns
6) K+ is released, Na+ can bind again
Active Transport (Bulk transport)
Endocytosis: cell takes in large quantities of material (membrane vesicles)
1) Phagocytosis: cells take in solid matter (ex: immune cells engulf pathogens)
2) Pinocytosis: take in liquid
Receptor mediated endocytosis: specific molecules bind to cell surface receptors + ingested by cell
Exocytosis (pathway): cell releases material (vesicles)
Ex: release of hormones or neurotransmitters
