Ion Channels and Transporters

Question 1

two general types of transport proteins

Answer 1

carrier and channel proteins

Question 2

channel proteins

Answer 2

discrimination based on size and charge

open channels and allow ions and water to slip through

movement is fast and direction is dependent on the solute concentration gradient

Question 3

carrier proteins

Answer 3

enzyme-like binding site for solute molecule

transmembrane transport involves conformational change

movemen of ions is slow and reversible

Question 4

two types of channels

Answer 4

ion-specific channels for ion permeability, found in most if not all cell types, used for inter-and intracellular signaling

non-specific channels - allow many kinds of molecules to pass through

Question 5

gap junction

Answer 5

comprised of six subunits in a hexagonal array and allows passage of water soluble molecules between cells

degree of opening of the junction is controlled by the concentration of intracellular ions

Question 6

alpha toxin

Answer 6

water soluble protein from staphylococcus aureus

forms a pore in the membrane of many cell types and allows passage of water-soluble, uncharged molecuels less than 2 kDa, ATP, and Ca2+

Question 7

two general types of carriers

Answer 7

transporters (or exchangers) - proteins that selectively ransport large water-soluble molecules and ions across membranes down their concentration gradient, facilitated diffusion

ATPases - transporters that couple transport with hydrolysis of ATP, energy expenditure allows movement up concentration gradient

Question 8

glucose transporters

Answer 8

a family of transporters that bind glucose on the EC surface and leads to release on the cytoplasmic side

driven by high EC glucose concentrations

Question 9

glucose-Na transporter

Answer 9

in some cells such as kidney tubules and intestinal cells, glucose concentration is too high, and this transporter binds NA+ and glucose simultaneously

transport is facilitaed by coupling it to the movemen of Na+ down its concentration gradient

Question 10

basic amino acid transporter

Answer 10

a Na+ independent transport of basic and neutral amino acids into cells

Question 11

neutotrasnmitter transporter

Answer 11

reseponsible for the reuptake of neurotransmitters at nerve terminals

Question 12

Na-H exchanger

Answer 12

couples the movement of Na+ into cells twith H+ out

since metabolic activity generates H ions, this exchanger helps regulate intracellular pH

Question 13

Na/K-ATPase

Answer 13

moves Na+ out and K+ into cells, responsible for creating Na+ and K+ concentration differences across the membrane

maintains cellular membrane potential and cell volume

uses about 25% of total energy consuption in humans at rest

Question 14

Ca-ATPase

Answer 14

transports Ca2+ out of cells or into organelles

maintains low intracellular Ca2+ level which is important in cell signalling

Question 15

H-ATPase

Answer 15

moves H+ out of the cell or into organelles

inmitochondria, this protein works in revers and generates ATP

Question 16

ABC transproters

Answer 16

a family of proteins with both transporter and ATPase activity

are used to move a wide variety of molecules into cells and organelles faster than would occur by simple diffusion

Question 17

How many subunits are ion-specific channels made up of?

Answer 17

six transmembrane domains

Question 18

How many subunits form the central pore region of a ion-specific channel?

Answer 18

four - allows ions to mvoe in and out of the cell

Question 19

How fast is the transition form an open to closed state in an ion-specific channel?

Answer 19

instantaneous

Question 20

mechanisms that affect ion-specific channel opening and closing

Answer 20

changes in membrane potential

binding of a ligand to the channel

mechanical stretching of the membrane

Question 21

two substates of close ion-specific channels

Answer 21

closed but activateable

close and inactivated

Question 22

two ways of reactivating inactivated ion-specific channels

Answer 22

changing of membrane potential or unbinding of ligand

Question 23

factors that affect the magnitude of the current through an open ion-specific channel

Answer 23

driving force (Vm - Eion) for the conducting ion and the duration that the channel stays open

current through an open channel obeys Oh’s Law (Iion = dV/Rm)

Question 24

probability that an ion-specific channel will open at a specified voltage or ligand concentration

Answer 24

follows a Poisson distribution (bell-shaped curve)

Question 25

types of ion-specific channels

Answer 25

ligand-dependent (or ligand-activated) channels

voltage-dependent (orvoltage-activated) channels

stress-activated channels

Question 26

ligand-dependent (or ligand-activated) channels

Answer 26

opened when a ligand binds to the channel

ex. neurotransmitter-activated, Ca-activated K channels, ATP-activated, cGMP-dependent

Question 27

voltage dependent (or voltage-activated) channels

Answer 27

channels are opened when the membrane potential is changed (either depolarized or hyperpolarized

Question 28

ion-specific channels opened by depolarization

Answer 28

Na-specific channels, Ca-specific channels

ubiquitous

Question 29

ion-specific channels opened by hyperpolarization

Answer 29

K-specific channels

ubiquitous

Question 30

stress-activated channels

Answer 30

opened when membrane is mechanically stretched

found in auditory receptors and cutaneous pressure receptors

Question 31

voltage-gated Na+ channels

Answer 31

composed of three subunits, alpha subunits has the critical functional properties

alpha subunit has 300-400 amino acid repeats

each repeat contains six predicted transmembrane domains

each repeat also contains a pore-loop (P-loop) whose residues line the pore

S4 transmembrane domains of residues function as sensors that move out during membrane coupled to channel opening

the intracellular domain has an inactivating mechanism that occludes ion conduction shortly after the channel opens

Question 32

ATPases

Answer 32

protines which couple transport with hydrolysis of ATP

energy expenditure enables movement of solutes up their concentration gradient

Question 33

Ouabain and digoxin

Answer 33

commonly used Na/K ATPase inhibitors used as glycosides

digoxin is commonly used as a cardiac glycoside to treat congestive heart failure

Question 34

Describe the mechanism of the SERCA Ca2+ pump

Answer 34

distinct E1 and E2 states

Question 35

two key structures of the SERCA pump

Answer 35

E1 Ca bound state and E2-P Ca unbound state

in the E2 state, the N and P domains have closed around the phosphorylaspartate analog and caused the calcium-binding site to be disrupted

Question 36

common functional domains of ion channels

Answer 36

selectivity pore, ion filter channel, gate

Question 37

domains of the serca pump

Answer 37

nucleotide binding domain (N)

actuator domain (A)

phosphorylation domain (P)

Question 38

stimuli that activate gated ion channels

Answer 38

voltage, extracellular ligand, intracellular ligand, mechanical forces

Question 39

describe the membrane topology of the voltage-gated ion channel

Answer 39

Question 40

What creates the selectivity filter?

Answer 40

created by loops between the fifth and sixth helix

Question 41

two broad categories of mammalian K+ channels

Answer 41

Question 42

structure of the bacterial two TM K+ channel

Answer 42

ions flow are selected by charge, selectivity filter lined by carbonyl oxygens

binding sites are very close together so the potassium ions electrostatically force each other through, creating a high flow rate