membrane transport Flashcards
what are 2 properties that influence whether a molecule can cross the plasma membrane without help?
- solubility of particle in lipid
- size
what is required for movement across a membrane? (2 general requirements)
- pathway
- driving force
what are the 2 driving forces a molecule can have to cross membrane?
- passive
- active (requires the cell to expend energy(ATP) to produce movement)
what drives molecules that passively cross membrane?
- diffusion down concentration gradient
- movement along an electrical gradient
can diffusion occur if membrane impermeable to substance?
NO
what is Fick’s law of diffusion?
several factors that influence the rate of net diffusion:
- The magnitude of the concentration gradient
- The surface area of the membrane across which diffusion is taking place
- The lipid solubility of the substance
- The molecular weight of the substance
- The distance through which diffusion must take place
what effect does increasing factors in Fick’s law have on rate of net diffusion?
a) increase conc gradient of substance?
b) increase surface area of membrane?
c) increase lipid solubility?
d) increase molecular weight of substance?
e) increase distance thickness?
a) increase rate of net diffusion
b) increase rate of net diffusion
c) increase rate of net diffusion
d) decrease rate of net diffusion
e) decrease rate of net diffusion
describe how ions move passively with electrical gradient?
= difference in charge between two adjacent areas generates an electrical gradient that promotes the movement of ions toward the area of opposite charge
->only ions that permeate the membrane can move along this gradient
how can ions cross with electrical gradient if can’t permeate membrane?
ion-specific channel proteins
- Leak (open all the time) or gated (open/close in response to stimuli)
what is electrochemical gradient?
The net effect of simultaneous electrical and concentration gradients on this ion
what is osmosis?
the net diffusion of water down its own concentration gradient through a selectively permeable membrane (from area of high solute concentration to low solute concentration)
what are aquaporins?
water channels
what is osmolarity?
concentration of osmotically active particles present in a solution
- Can be calculated or measured
- Units: osmoles (Osm) of solute per litre (Osm/l or osmol/l)
- Body fluids: ~300 mOsm/l
what is tonicity?
effect a solution has on cell volume (no units)
what is isotonic?
when place cells in solution →no change in cell volume
what is hypotonic?
when place cells in solution →increase in cell volume as movement of water from outside to inside the cell
what is hypertonic?
higher conc of solutes outside cell rather than inside
- decrease in cell volume due to losing water to extracellular environment
what is carrier mediated transport?
Substance binds onto a specific carrier which undergoes a conformational change which transports the substance
what are the 3 important characteristics that determine the kind & amount of material transferred across the membrane?
- specificity (each carrier is specialised to transport specific substance)
- saturation (transport gets saturated at certain point)
- competition
what are 2 forms of carrier mediated transport?
- facilitated diffusion
- active transport
what is facilitated diffusion?
uses a carrier to facilitate (assist) the transfer of a substance across the membrane ‘downhill’ from high to low concentration ( doesn’t require energy)
what is active transport?
requires the carrier to expend energy to transfer a substance ‘uphill’ against a concentration gradient
what is primary transport type of active transport?
Energy is directly required to move a substance against its concentration gradient
what is secondary transport of active transport?
- Energy is required, but it is not used directly to produce ‘uphill’ movement.
- The carrier does not split ATP – instead it moves a molecule ‘uphill’ by using secondhand energy stored in the form of an ion concentration gradient (usually a Na+ gradient)
what are 3 important roles of Na/K pump?
- Helps establish Na+ and K+ concentration gradients across the plasma membrane of all cells (next GRC lecture).
- Helps regulate cell volume by controlling concentration of solutes inside the cell.
- The energy used to drive the pump indirectly serves as the energy source for secondary active transport.
what does Na/K pump transport?
3 sodium out and 2 potassium in (SOPI)
what is secondary active transport?
transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (Na+)
what are the 2 mechanisms that secondary active transport can occur by?
- symport (solute & Na+ move at same time)
- antiport (solute & Na+ move in opposite directions)
what is vesicular transport?
Requires energy for vesicle formation and movement within the cell (active)
e.g. endocytosis & exocytosis
