Chapter 8: membrane transport and electrochemical signaling Flashcards
The meaning of selectively permeable
- they only allow some molecules to enter or exit cell
• Know which types of molecules can pass through the membrane & the rates at which they do so
- small np: (co2, o2)moves through membrane quickly w/o help
- small uncharged p: (h2o, ethanol) difficult to pass through membrane because uncharged, can if given time but at much slower rate than 1.
- larger uncharged p: same as above but slower (speed dependent on size and polarity)
- ions: cant move through w/o help
The nature of diffusion and example
- tendency of molecules to spread out evenly into an available space
- high to low
- cells need o2 for CR, rbcs deliver o2 (h) and release it, cells use o2 for CR, as long as cells continue to use o2 the conc. grad remains high and o2 diffuses.
Nature of osmosis and example
- Osmosis: diffusion of water across selectively permeable membrane.
- Aquaorins: always open-> small pores that allow quick passage for water. Allow h2o to move freely across membrane based on conc. grad. water always moves to side that has higher coc. of solute to dilute it.
Nature of tonicity and example
- hypotonic: + solutes inside cell -> water enters to dilute
- isotonic: = conc. no movement h2o
- hypertonic: + solutes outside -> h2o leaves to dilute.
Types of passive transport and components involved
- Diffusion of sub. across mem. high to low, no energy required.
- simple: directly through mem.
- Facilitated: through protein channel or transporter
- Transporters undergo conformational change that expose the solute-binding site
first on one side then other. - channels form continuous pores that interact w/ solutes weakly, differentiate by size and charge
Types of active transport and components involved
- AT: movement of solutes against conc. gradient. requiring energy carried out by pumps.
- primary active transport: requires energy provided by atp (atp driven pump)
- secondary: energy provided by moving ion down conc. grad. at same time as another sub. is transported (gradient driven pump)
- uniporters: move of single solute
- coupled transport: two sub moved at once, one against and one with conc. gradient.
- symporter: simultaneous coupled transport of both solutes in same direction
- antiporter: opposite
The nature of membrane potential and how it’s achieved by using electrochemical gradients (including
resting membrane potential)
MP: electrical (-) across the membrane, inside to out.
- ions travel down ecg, involves icg/mp. They will always travel to the side that as opposite charge or lower concentration.
- cells regulate mp by moving ions back and forth
- high na outside cell, high k and (-) inside cell, inside cell -
- k leak channels are integral in maintianing mp in animal cells, when open, the k leaks out and travels outside cell with their conc. gradient (lower conc). Once 1 k leaves this produces -> uneven - -> mp. K will stop leaving cell when mp is large enough to overcome concentration gradient.
RMP: electrical potential difference across membrane when the cell is in a non-excited state.
• How ion channels work. Includes their structure & how their function is connected to the membrane
potential
- selective based on charge and size
- must shed h2o to fit
- 1000 x faster than Transporter, no cc
- cell stimulated? ion channels open and cause change in MIP
- whether ion leaves/enters cell dependent on ECG
- MP dependent on ic and ion conc. either side
- quick changes in mp utilized to propagate electrochem signals
- ion channels differ based on gating mechanisms and channel specificity.
• The mechanism of how glucose is taken up by gut epithelia and transported to the bloodstream. Also,
how sodium is involved
1.
- to use glucose transport into ec and then into bloodstream
- 2 diffferent glucose transporters : uni adn sym (3cc)
- the rapid uptake of glucose provides high conc. inside cell
- glucose leaves and enters bs through a uni found on basal membrane, h2l
2.
- to create cg (high glucose in cell and low in bs) energy is needed to pump g from apical membrane using a na driven symporter.
- to move glucose against gradient, it uses the naturally high concentration of na outside cell as enreegy to transport it.
- remember that high ecg = pe, and that because we are trying to move glucose agaisnt its gradient we need energy. When na moves with its gradient simultaneously as this, it provides that energy needed.
3. to maintain the na conc. grad. and the uptake of glucose, an antiporter (na k atpase) is needed
- it uses pat = requires atp to maintain ion balance
- exchanges 2 k for 3 na
- na goes out and k goes in
- this uneven distribution of ions maintians voltage across membrane
how glucose is taken up by skeletal muscle cells
- high levels of glucose in the bloodstream triggers the pancreas to secrete insulin
- when the insulin reaches the membranes of the liver or fat, it triggers the cells to display a uniporter called GLUT 4
- GLUT 4 uses pt to import glucose
- Once glucose enters cell it is immediately phosphorylated into glucose 6 phosphate
- Enter glycolysis or be stored as glycogen
- This ensures that the conc. grad. of g remains high outside and low inside.
The nature of mechanically-gated channels and the structure/components of auditory hair cells. How do
they produce an action potential?
- auditory hair cells in ear use mechanically gated channels
- hair cells are wedged between the basilar and tectorial membranes, that have stereocilia where mc receptors are rich.
- when there are sound vibrations, this pushes against basilar which pushes against sc which pushes against tectorial membrane which causes them to tilt.
- filaments link sc together
- when the sound causes them to tilt, the filaments pull open a channel that allows a nerve impulse to be sent to the brain.
The structure of neurons
cell body: nucleus within
- cytoplasmic extensions: dendrites and axons
- axons have long single axon responsible for transmitting signals to next neuron in line, and the terminal end of the axon branches off to transmit signals to multiple targets simultaneously
- there are many branched dendrites off the cell body and they are responsible for giving large SA for receiving signals and transmitting them to cell body.
The phases of action potentials and the mechanism of ion channels/transporters involved in each phase
- nerve cell at rest
- outside + with high na and low k
- inside - with high k and low na - Nerve impulse starts: Na channels open
- outside + with high na and low k
- inside - with high k and low na - Depolarization: na enters cell
- outside - with low na and low k
- inside + with high na and high k - Start of repolarization: na channels close and k channels open
- outside - with low na and low k
- inside + with high na and high k - repolarization: k exits cell and charges flip back
- outside + with high k and low na
- inside - with high na and low k - Reset: k channel closes, na and k pumps reset gradient, 3 for 2 ratio w/ atp
- outside + with high k and low na
- inside - with high na and low k - Nerve cell at rest:
- outside + with high na and low k
- inside - with high k and low na
• How action potentials are generated and how the membrane potential is restored after
- to produce ap the original mp has to be reset
- following depolarization, na channels close and k channels open (repolarization)
- repolarization is flooding k out of cell down grad. the loss of the k ions causes inside of cell to be less + and more -
- voltage gated k channels are slower to open and close causing hyperpolarization
- hyperpolarization is cell becomes more - than usual due to more k ions flooding out of cell than intended
- the na/k pump resets the grad. on either side of membrane, restoring membrane potential.
