Ch. 12 Membrane Transport & Potential, Ion Channels, Nerve Cell Signalling Flashcards
define ion channels
membrane proteins in plasma membrane transporting inorganic ions thru cell
how can sugars and amino acids be transported
thru transport proteins
define transporters
proteins with moving parts that can shift small molecules from one side of membrane to other thru conformation shape change (carrier proteins)
define channel proteins
proteins that form small hydrophillic pores allowing solutes to pass by thru simple diffusion
describe the plasma membrane
semi-permeable, blocks passage of almost all water-soluble molecules due to double layer of phospholipid
what does the ability of a molecule to diffuse depend on; if they can’t simple diffuse across the plasma membrane, what is required
polarity and hydrophobicity; transport proteins
what are examples of small, non-polar molecules
gases, steroids, hormones
what are examples of small uncharged polar molecules
water, ethanol, glycerol
what are examples of large uncharged polar molecules
amino acids, glucose, nucleosides
what are the main characteristics of transporter proteins
- specificity
- competition
- saturation
what are the categories of transport; briefly describe each
- passive (high to low therefore no energy needed)
- active (low to high needing energy)
there can be specific transport proteins for cell types. one example is transporters for skeletal muscle cells using Ca+2, describe the flow of Ca+2 regarding if a pump/energy is needed
- Ca ion flows from sarcoplasmic reticulum to cytosol thru ion channels
- cell contracts
- Ca returns to SR thru Ca pump (transporter) activated by phosphorylation
- active process
glucose is able to travel thru liver cells using transporters, describe its pathway
- direction depends on gluc. conc.
- if ↑ outside liver cell and ↓ inside (after meal for EX) then gluc uses transporters to travel into liver cell
- if ↓ outside and ↑ inside liver cell (when hungry for EX) then liver cell will breakdown glycogen and release glucose to outside of cell using transporters
- only maintains passive pathway (along the gradient)
what are the types of transporters
- uniport
- symport
- antiport
define uniport transporters
carrying only one substance
define symport transporters
- cotransport
- two substances in same direction
define antiport
- countertransport
- two substances moving in opposite directions
what are the types of coupled transport
symport and antiport bc movement of one molecule is tied to movement of the other
describe p-glycoprotein; where is it found
- transport protein
- found in renal tubules, microvessels (brain), GI tract
- eliminates toxins
- absorbs, distributes, eliminates drugs
thruout history, people ate poisonous foods but didn’t die. how so?
- p-glycoprotein gets rid of toxins
- overabundance of p-glyc. pumps the drug out of the body instead of absorption
what drug transport is responsible for multidrug resistance in cancer cells
p-glycoprotein
what does the movement of ions depend on
electrochemical gradient (solute concentration and membrane voltage)
draw pathways of strong and weak flows of ions into and out of cell
strong: voltage and concentration gradients work in same direction (opposite charge movement)
weak: voltage and conc gradients work in opposite directions (same charge movement)
how many Na and K enter or exit cell
3 Na out, 2 K in (net 1 Na out)
draw out the pathway of the Na/K pump with each step
- na binds
- pump phosphorylates itself thru ATP hydrolysis
- p causes conformational shape change which ejects Na into extracellular space
- K binds
- pump dephosphorylates
- pump returns to original conformation and K is ejected into cytosol
cells are able to use high concentrations of _____ on the outside of cell as potential energy
sodium ion
how are cellular processes triggered; why?
- thru energy from Na+
- if outside of cell has higher Na conc then inside it generates powerful energy force
- at anytime the cell can make an opening in its plasma membrane allowing Na to flow inside
- since inside of cell has net negative charge and low na conc, na rushes to go inside cell (caused by ion channels)
describe key characteristics of ion channels
- selective (selectivity filter is lined by carbonyl channel)
- brief opening and closing
- respond to dif stimuli
what does ion selectivity depend on
- size of channel pore (large 4 large)
- charge of pore lining (net - conducts + ions, vice versa)
what causes overall charge of pore lining
amino acids making up lining of pore
describe the plasma membrane of a cell
hydrophobic, selectively permeable
what is made when an ion channel opens
aqueous pore
what are the types of ion channels; briefly describe each
- voltage-gated (changes in membrane potential)
- ligand-gated (binding of other molecules called ligands)
- mechanically-gated (physical stimulation)
define ligands; what are the types of ligands
- stimulating molecules that cause ion channels to open/close
- intra/extra- cellular
give an example of a mechanically-gated channel
auditory hair cells have mechanical gates that open due to vibrations
define membrane potential
- electrical diff between inside and outside of cell
- cation + and anion -
how does electrical current occur and how is it regulated
- ion flow across membrane
- ion channels
in what situations do cells not have a membrane potential
equal concentrations of +/- ions on either side of cell
define resting membrane potential; what it is the direct result of
- -20 to -200mV (neg due to inside)
- membrane potential under steady state
- direct result of dif in K+ ion conc. in and outside of cell
what is the main contributor to membrane potential
K+ leak channels
if K+ leak channels are present and they play a major role in membrane potential, how is it possible for the membrane potential to be zero
pos and neg charges balance out on both sides of cell even if K+ conc. is higher on one side
describe K+ ion movement
- down conc. gradient
- when they travel to outside of cell, they leave - counterions unable to pass thru K+ leak channel
what is nernst equation used for
- membrane potential when ion conc on inside and outside of cell are known
how are electrical signals thru ions transmitted
neurons
draw out a neuron including nucleus, axon, terminal and axon terminal branches, body, dendrites
…
describe the movement of electrical signals in neurons
- stimulus causes small change in membrane potential for cell body
- travel thru axon due to electrical excitation (action potential) b/c depolarization leads to more depolarization
describe what happens in an action potential
- stimulus: neurotransmitters bind to receptors of dendrites, bringing mem. pot. closer to zero (depolarization)
- repeated depolarization brings cell to threshold value which triggers opening of many Na+ channels
- Na+ flows inside cell until it reaches peak which make K+ ion channels open and Na+ channels inactivated
- K+ ions flow outside of cell (repolar.) causing cell to become more - than rest. mem. pot. (hyperpolar.)
- return to resting pot. and Na+ channels close
in order for action potential to go to a cell, it must be converted to; transmitted at
- chemical signal (neurotransmitter)
- junctions called synapses
draw out pre and post synaptic cells connected by a dendrite; include nerve terminal, membranes, synaptic cleft
…
where are neurotransmitters stored
synaptic vesicles
describe pathway of action potential to target cell
AP received by pre-synaptic nerve terminal and passes through presynaptic and postsynaptic membranes to postsynaptic cell though connection by dendrite
neurotransmitters are released when what channels are opne
Ca+2 voltage gated channels
draw out movement of NT thru resting nerve terminal to NT receptor
no movement bc Ca+2 channel is closed
draw out movement of NT thru activated nerve terminal to NT receptor
ca+2 enters thru channel due to nerve impulse in pre-synaptic nerve terminal which makes synaptic vesicles fuse with membrane of terminal and release nt contents into cleft
another name for neurotransmitter receptors is
transmitted-gated ion channels
what happens when NTs bind to NT receptors
conformational shape change of NT receptor occurs which lets ions flow into post synaptic cell and change membrane potential
draw out an active synapse
….
decsribe the structure of the neurotransmitter receptor/gated ion channel
- 5 similar subunit proteins arranged in a circle making a pore at the top
- each has a binding site
- attached to lipid bilayer on cytosol
draw out overall, closed and open NT receptors
…
describe excitatory neurons
release excitatory NTs which bind to receptors that make action potentials
describe how opening of Na+ channels are excitatory
excitatory synapse and exc. NT bind to e/o which opens Na+ channels leading to depolarization and increases likelihood of firing action potential
describe inhibitory neurons
neurons that release inhibitory NTs that bind to receptors and decrease chances of action potential made
describe how opening of Cl- ion channels are inhibitory
inhibitory synapse and inhib. NT bind which keeps membrane polarized and decreases the likelihood of action potential happening
describe GABA
- gamma-aminobutyric acid
- inhibitory NT
- conducts Cl- ions reducing firing of AP
how are valium and GABA gated-Cl- channels related
- bind with e/o
- makes cell more sensitive to GABA’s inhibitory action
- enhances GABAs ability to reduce neuron firing
why are drugs, like valium, xanax, and romazicon considered sedative
- make cell more sensitive to GABAs NT in brain (release more)
- calms and sedates person taking it (i.e. can treat anxiety)
how can NTs on postsynaptic cell be gotten rid of
- destruction by enzymes
- reuptake
- diffusion
