1.4 MEMBRANE TRANSPORT Flashcards
Potassium channel overview
Potassium channels in axons are voltage gated.
They enable the facilitate diffusion of potassium out of the axon
Potassium channels
Facilitated diffusion
Step 1
At one stage during a nerve impulse there are relatively more positive charges inside
Potassium channels
Facilitated diffusion
Step 2
This voltage change causes potassium channels to open.
Allowing potassium to diffuse out of the axon.
Potassium
Channels
Facilitated diffusion
Step 3
Once the voltage conditions change the then the channel rapidly closes again
Sodium-potassium pump overview
Na-K pump follows a repeating cycle of steps that result in 3 Na ions being pumped out of the axon (of the neutron) and 2 K ions being pumped in
Each time the pump goes round this cycle it uses one ATP–> active transport
Na-K pump
Active transport
Step 1
The interior of the pimp is open to the inside of the axon
3 Na enter the pump and attach to their binding site
Na-K pump
Active transport
Step 2
ATP transfers a phosphate group from itself to the pump
This causes the pump to change shape and the interior is then closed
Na-K pump
Active transport
Step 3
The interior of the pump opens to the outside of the axon
3 Na ions are released
Na-K pump
Active transport
Step 4
2 K ions from outside enter and attach to their binding site
Na-K pump
Active transport
Step 5
Binding of K causes the release of the phosphate group
This causes the pump to change shape again
So that it is again only open to the inside of the axon
Na-K pump
Active transport
Step 6
The interior of the pump opens to the inside of the axon and the two K ions are release
Na-K pump
Active transport
Final step
Sodium ions can now enter and bind to the pump again
Step 1
Factors affecting rate of diffusion through a partially permeable membrane
High conc gradient = high rate
Short diffusion path = high
High/large SA =faster rate
Adaptations in biology in maintaining concentration gradient
REDUCING LENGTH OF DIFFUSION PATH
membranes are of thin (7-10 nm)
Folded membranes increase SA:VOL
More membranes in a smaller volume = shorter distance
MAXIMISING S.A for absorption Alveoli in lungs Membrane folds in mitochondria Root hair for water: mineral ions uptake Villi for absorption
Vesicle movement in cells
Vesicles are small spheroidal packages that bud off the RER and Golgi apparatus
Carry proteins produced by ribosomes on RER to Golgi apparatus
–> prepared for export from cell via another vesicle
EXOCYTOSIS
The fluidity of membranes allow materials to be released
“Release of substances from a cell (secretion) where a vesicle fuses with the cell plasma membrane”
Used to remove waste products
ENDOCYTOSIS
The fluidity of membranes allows materials to be taken into cells
“Taking in of external substances by an inward pouching of the plasma membrane, forming a vesicle”
To form a vesicle a small region of plasma membrane is pulled from the rest and pinched off
Placenta: protein/ antibodies from mother’s blood absorbed into foetus by endocytosis
VESICLE
Small sac of membrane with droplet of fluid inside
Preventing osmosis in excised tissue and organs
Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis
Isotonic saline solution useful for preventing damage to cells and tissues + donor organ transportation
Different osmosis states
Hypertonic sol - plasmolysed cell: more water leaving
Isotonic sol - flaccid cell equilibrium
Hypotonic sol- turgid cell more in
