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Flashcards in Chapter Twelve Deck (52):


allows passage to solute mols that fit into transporter's binding site changes conformation, selective bc of specific binding



discriminates btwn solutes (ions) mostly on basis of size + charge; leaky/opening/closing controlled by external stimulus (e.g. ligand gated); ion selective faster . than . channels


simple diffusion

small uncharged solutes move down concentration gradients (e.g. small steroids, ethanol, CO2, O2)


facilitated diffusion

transport/channel protein needed; transporters are only ones to do active transport (E is required)


voltage and concentration in electrochem. gradient

in same direction: Na+ enters cell readily; in opposite directions: K+ wants to leave cell but V across exterior of cell opposes it; net charge moving solute (ions) across membrane is CG+V across membrane (electrochem. gradient = driving F determines direction of facilitated passive transport across membrane)


biological gradients

potential E used to do work; ADP and inorganic phosphate with ATP synthase; ATP synthesized in mitochondria by ATP synthase; Hydrogen ion gradient: 3 H ions = 1 ATP


ionic balance + avoiding osmotic swelling in protozoa

contractile vacuoles that periodically discharge contents


ionic balance + avoiding osmotic swelling in plant cells

water vacuoles + cell walls collect water until full tugor allowing stems to be rigid


ATP synthase

production of ATP in mitchondria


ADP/ATP translocase

lets ATP/ADP to cross inner mitochondria; ATP produced from oxidative phosphoriation from mito matrix to cytoplasm; ADP from cytoplasm to mito matrix


conformational change in transporter protein

passive transport of solute (e.g. glucose); glucose taken up by cells passively in direction of CG by transporters


pumps carry out active transport in 3 ways

(1) couple uphill (e.g. Na+) transport of 1 solute across membrane w downhill (e.g. Na+) transport of another (2) couple uphill transport to hydrolysis of ATP (3) uphill transport to input of E from light (e.g. bacteriorhodopsin protein used by Halobacteria captures light E + resulting proton grad is converted into chem E)


Na+/K+ pump

E from ATP hydrolysis to pump Na+ out of animal cells and K+ in (conformational change)


cardiac failure

ouabain and digitoxin used to increase contraction in cardiac muscle cell by binding to K+ binding sites + inhibiting so Na+ cont. leaks into cell; cell uses alt Na+/Ca2+ pump so Ca2+ pumped into heart smooth muscle cell causing involuntary contraction


xray crystallography

Ca2+ pump in SR was 1st ATP driven ion pump to have its 3D structure determined by xray crystallography


normal muscle contraction

skeletal muscle cell stimulated - Ca2+ flood into cytosol from stores in ER - cell contracts


muscle cell recovery

Ca2+ must be returned to SR - facilitated by Ca2+ channel pump, phosphorlayation of active sites via ATP triggers rearrangement of transmembrane helices releasing Ca2+ to SR lumen


transporter proteins can function as

uniports, symports, or antiports; active or passive transport; coupled transporters act as pumps that couple uphill transport of one solute to the downhill transport of another


glucose Na+ symport protein uses elctrochem Na+ gradient to drive active transport of glucose

pump moves from occuluded occupied to occluded empty state but cannot act unless transition involves binding of both solutes to their specific binding sites @ same time; bc concent. of Na+ is much higher outside than inside cell, must wait until rarer glucose mol binds its specific site


two types of glucose carriers enable gut epithelial cells to transfer glucose across the epithelial gut lining

glucose concentration in luminal cell is high so glucose is actively transported from gut lumen into epithelial cell (Na driven glucose transporter aka symport at apical surface against gradient); glucose is then released from epithelial cell in ECM and into blood down its concentration gradient by passive glucose transporter aka uniport at the basal surfaces


H+ATPase pump

used drive H+ across the membranes of plant and animal cells; lysosomes in animal cells and vacuoles in plant cells contain H+ATPase in their membranes pumping H+ in via ATPase pump keeps the H+ interiors of each continuously acidic


ion channel selectivity filter

controls which inorganic ions it will allow to cross the membrane


ion selectivity depends upon

diameter and shape of ion channel and distribution of charged AA in lining: channel is narrow enough in places to allow ions of appropriate size and charge to pass


what limits the number of ions?

ions shed associated water molecules and pass single file marking transient contact w atoms that line filter this limits through saturation


gated ion channel

fluctuates btwn closed and open conformation; controlled w huge adv over transporter protein more than a million ions can pass through channel each sec BUT cannot couple ion flow w E source therefore can't carry out active transport make membs pereable to ions so diffuse down concentration gradients when gates are open


venus flytrap uses electrical signaling to capture its prey

fly moves trigger hairs to produce mechanical stimulation: open ion channels (H+ and Ca2+), translated into electrical signal (inc in +ions causes depolarization), propagated down the leaf changing turgor pressure (water enters in response to inc acidity/hypertonicity) in the leaf lobes, snapping leaf shut and ending the fly's happy days


membrane potential

distribution of ions on either side of a cell membrane gives rise to its membrane potential; ions flow across a membrane detected as an electric current; accumulation of ions (if not exactly balanced w ions of opposite charge) will be detected as a change in membrane potential


K+ concentration gradient and K+ leak cahnnels

major roles in generating the resting membrane potential across the PM in animal cells; more K+ inside than outside K+ channels always open K+ leaks out; but more pos outside the cell so K+ is retarded and leaks out of the cell very slowly


gated ion channels open/close in response to different types of stimuli

(1) ion selectivity (types of ions that can pass) (2) gating (the conditions that influence their opening and closing) (3) specificity (response to different stimuli)


mechanically gated ion channels allows us to hear

(1) vibrations via "ossicles" sets fluid in tympanic canal in motion (2) vibrations transmitted to basilar membrane in Organ of Corti (3) membrane vibrates (4) sterocilia of hair cells rub up against overlying tectorial membrane (5) K+ and Ca2+ move across cell membranes changing membrane potential hair cells sending action potential via cochlear nerve to CNS


leaf closing response in touch sensitive plant Mimosa pudica

(a) resting leaf (b) mechanical stimulus causes opening of K+ ion channels down the leaf generating an electrical impulse which reaches specialized hinge cells at base of each leaflet (c) voltage activated channels in hinge cells now open leading to rapid loss of water and electrolytes causing collapse of leaves which now fold


components of typical neuron

cell body, single axon, multiple dendrites


cell body and dendrites

receiving signals from other neurons



connects cells bodies


terminal branches

passes signal to other target cell e.g. neurons, muscles and glands


resting potential in unstimulated neurons

electrical potential of a neuron or other excitable cell relative to its surroundings when not stimulated or involved in passage of an impulse (~-70mV)


resting potential is primarily maintained by

(1) Na+/K+ pumps that balance Na+/K+ cation flux (2) open K+ concentration gradient/leak channels (fig 12.22) balanced w few open Na+ leak channels (3) large proteins carrying anionic charge and other anionic charge and other anions that remain inside cell


electrical, chemical or mechanical stimulus can alter a cell's resting potential by

(1) increasing the membrane's permeability to various cations (mostly Na+, K+, Ca2+) (2) providing a transient graded potential that usually fades out w/i a few mm of point of origin


cells like neurons, muscle cells (e.g. cardiac contractile cells) a stimulus can generate an action potential

AP have fixed amplitude and time course and are basically all or nothing


AP triggered by

depolarization of neuron's PM


(1) excitation: membrane depolarizes

V activated K+ channels remains closed; V activated Na+ channels open Na+ moves into cell; threshold -55mV is passed; reaches pos "spike"


(2) membrane slowly repolarizes

V activated Na+ channels close; V activated K+ channels open K+ moves out of cell; membrane potential becomes more neg


(3) membrane is now in refractory state

bc Na+ gates are inactivated and no more depolarization can occur; membrane moves back to resting potential; once Na+ gates reset another AP can occur


voltage gated Na+ channel can flip from one conformation to another depending on

membrane potential


V gated Na+ channels change their conformaiton during an action potential

initial stimulation triggers an AP; even if restimulated the PM can't produce a second AP; not until the Na+ channels have returned from the inactivated to the closed (reactivated) position


continuous conduction

un-myelinated neurons: no nodes of ranvier, involves entire axon PM (smooth and progressive), speed of transmission is proportional to diameter of axon, larger axon faster transmission (reduced internal resistance), squids have giant axons to escape predators


saltatory conduction

in myelinated neurons: bc of myelin sheath, PM makes direct contact w surrounding ECF ONLY at Nodes of Ranvier where signal transmitted and APs occur, AP "jumps" from node to node, depolarization (Na+) moves rapidly down axon


action potential propagates along length of axon

changes in Na+ channels and flow of Na+ down the memb alter MP and cause a travelling AP; AP can only travel forward from site of depolarization bc Na+ channel inactivation prevents depolarization from spreading backward


neurons connect to target cells at synapses

AP continues down length of neuron until reaches synaptic terminal at end of presynaptic neuron


electrical signal converted into

secreted chem signal at a nerve terminal which is then converted into an electrical signal by post synaptic ligand gated ion channels at the synapse


acetylcholine receptor

is present in PM of skeletal muscle cells, opens when binds acetylcholine and Na+ ions can pass; ACh R is a ligand gated ion channel composed of 5 transmembrane protein (alpha helices) subunits; acetylcholine binds protein changes shape and opens; Na+ flow across membrane down electrochemical gradient; (-) charged AA side chains at either end of pore ensure that mainly Na+ pass


thousands of synapses form on cell body and dendrites of a motor neuron in the spinal cord

deliver signals from other parts of the animal to control the firing of APs along the neurons axon