Chapter 13. Membrane Channels and Pumps

Question 1

a phenomenon observed in cancer cells in which the development of resistance to one drug renders the cells resistance to a range of other drugs. The resistance is due to the action of an ATP-dependent pump called the multidrug resistance protein (MDR), which contains an ABC domain.

Answer 1

Multidrug resistance

Question 2

ATP-dependent pump, containing an ABC domain, that pumps drugs out of a cell.

Answer 2

Multidrug-resistance (MDR) protein (P–glycoprotein)

Question 3

Compounds derived from cholesterol that inhibit the Na+-K+ pump by blocking the dephosphorylation of the E2 conformation of the pump protein. Inhibition of the pump in cardiactissue cells leads to a higher level of sodium ion in the cells, which slows the extrusion of calcium ion and enhances cardiac muscle contractility.

Answer 3

Cardiotonic steroid

Question 4

family of enzymes that uses the energy of hydrolysis to move ions across membranes. They are called P-type ATPases because the reaction mechanism includes a phosphoaspartate intermediate.

Answer 4

P-type ATPase

Question 5

The interconverting of a site on a membrane protein from one of exposure to the extracellular environment to one of exposure to the intracellular environment.

Answer 5

Eversion

Question 6

the ATP-binding domain characteristic of specific membrane transport proteins, called ABC transporters. These transporters also contain a membrane spanning region.

Answer 6

ATP-binding cassette (ABC) domain

Question 7

Membrane proteins that use the energy of ATP hydrolysis to drive the thermodynamically uphill transport of ions or molecules.

Answer 7

ATP-driven pump

Question 8

Protein channels that transport water across membranes.

Answer 8

aquaporin

Question 9

A membrane protein that is responsible for pumping sufficient protons into the stomach, at the expense of ATP hydrolysis, to lower the pH to 1.0.

Answer 9

Gastric H+–K+ ATPase

Question 10

The increase in membrane potential and the changes in sodium and potassium conductances that result from alterations in the permeability of the axon membrane to those ions. Also called nerve impulse.

Answer 10

Action potential

Question 11

A ligand-gated channel that promotes a large inward current of sodium ions and triggers an action potential; composed of a pentamer of four kinds of polypeptide subunits, the channel opens to allow passage of sodium and potassium ions when two acetylcholine molecules promote transient opening of the channel.

Answer 11

Acetylcholine receptor

Question 12

Membrane proteins that mediate the transport of ions and small molecules across the membrane without consumption of ATP.

Answer 12

Carrier

Question 13

transport of an ion or a molecule against a concentration gradient, where delta G for the transported species is positive, and where the process must be coupled to input of free energy from a source such as ATP, an electrochemical gradient of Na+ or K+, or light.

Answer 13

Active transport

Question 14

a transport system in which a molecule is carried across the membrane in the same direction as an ion, which in turn is pumped back across the membrane through active transport linked to ATP consumption.

Answer 14

Antitransporter (symporter)

Question 15

a mixture of cardiotonic steroids derived from the dried leaf of the foxglove plant. Such steroids inhibit the sodium-potassium pump.

Answer 15

Digitalis

Question 16

Membrane proteins that catalyze active transport and contain ATP binding (ABC) cassettes.

Answer 16

ABC transporter

Question 17

A common neurotransmitter that exerts its effects by first binding to the acetylcholine receptor.

Answer 17

Acetylcholine

Question 18

These proteins couple the downhill (exergonic) flow of one species to the uphill (endergonic) flow of another in the opposite direction across the membrane.

Answer 18

antiporter

Question 19

A symporter that uses the H+ gradient across the E. coli membrane (outside has higher H+ concentration) generated by the oxidation of fuel molecules to drive the uptake of lactose and other sugars against a concentration gradient.

Answer 19

Lactose permease

Question 20

A model for the regulation of the K+ channel that postulates that the first 20 residues of the K+ channel form a cytoplasmic unit (the ball) that is attached to a flexible segment of the polypeptide (the chain). When the channel is closed, the ball rotates freely in the aqueous solution. When the channel opens, the ball quickly finds a complementary site in the open pore and occludes it.

Answer 20

Ball-and-chain model

Question 21

passive transport systems for ions capable of very high transport rates. Ion channels often display a high degree of specificity for the transported ion.

Answer 21

Ion channel

Question 22

A membrane protein that transports Ca2+ out of the cytoplasm and into the sarcoplasmic reticulum of muscle cells at the expense of ATP hydrolysis.

Answer 22

Sarcoplasmic reticulum Ca2+ ATPase (SERCA)

Question 23

The movement of lipophilic molecules through a membrane down their concentration gradient.

Answer 23

Simple diffusion

Question 24

A process in which the free energy of ATP hydrolysis is used to drive the movement of ions against their concentration gradients.

Answer 24

Primary active transport

Question 25

a transporter that uses the energy of the downhill (exergonic) flow of one ion or molecule to power the uphill (endergonic) flow of another.

Answer 25

Secondary transporter (cotransporter)

Question 26

Membrane proteins that provide a pore through which ions can flow very rapidly in a thermodynamically downhill direction.

Answer 26

Channel

Question 27

Transport of an ion or a molecule down a concentration gradient, where .G for the transported species is negative. Also called passive transport.

Answer 27

Facilitated diffusion (passive transport)

Question 28

a method for studying ion channels in which a high-resistance seal is formed between a pipette and a small patch of plasma membrane, allowing the monitoring of the flow of ions through a single channel with high time resolution.

Answer 28

Patch-clamp technique

Question 29

Six connexin molecules hexagonally arrayed to form a half-channel. Two connexons form a functional gap junction.

Answer 29

Connexon (hemichannel)

Question 30

A thermodynamic measure of the energy resulting from an unequal distribution of a population of molecules across a membrane that takes in account concentration differences and charge differences between the two sides of the membrane.

Answer 30

Electrochemical potential (membrane potential)

Question 31

The equilibrium achieved when the driving force due to a concentration gradient is balanced by an electrostatic force resisting the motion of additional charges; applies to a membrane separating two different concentrations of ion with a channel connecting the two sides of the membrane.

Answer 31

Equilibrium potential

Question 32

The increase in membrane potential and the changes in sodium and potassium conductances that result from alterations in the permeability of the axon membrane to those ions. Also called action potential.

Answer 32

Nerve impulse

Question 33

A member of a family of membrane-spanning proteins with molecular masses ranging from 30 to 42 kd. Each connexin molecule appears to have four membrane-spanning helices. Connexin is a component of gap junctions.

Answer 33

Connexin

Question 34

a high-resistance seal formed between a pipette and a small patch of plasma membrane required for use in the patch-clamp technique.

Answer 34

Gigaseal

Question 35

A protein passage in a membrane that can transport a molecule from one compartment to another against a concentration gradient; pumps undergo a cycle of conformational changes that alter the affinity of the binding site for the transported molecule, and the eversion of the molecule during the cycle is driven by expenditure of free energy. Also called active transporters.

Answer 35

Pump

Question 36

small, diffusible molecules like acetylcholine that mediate the passage of nerve impulses across the synapse.

Answer 36

Neurotransmitter

Question 37

The process in which carriers utilize the gradient of an ion to drive the transport of another molecule against its gradient.

Answer 37

secondary active transport

Question 38

An enzyme that hydrolyzes ATP to generate ionic gradients by pumping Na+ out of the cell and K+ into the cell.

Answer 38

Na+ -K+ pump (Na+ -K+ ATPase)

Question 39

The space between the presynaptic membrane of one nerve cell and the postsynaptic membrane of an adjacent nerve cell.

Answer 39

Synaptic cleft

Question 40

Veq = -(RT/zF) ln ([X]in/[X]out) where R is the gas constant and F is the Faraday constant (96.5 kJ V&sup-1; mol&sup-1;, or 23.1 kcal V&sup-1; mol&sup-1;) and z is the charge on the ion X (e.g., +1 for X+).

Answer 40

Nernst equation

Question 41

a transmembrane channel that is opened by the binding of a one or more molecules to a ligand-binding domain of the channel protein.

Answer 41

Ligand-gated channel

Question 42

Passageways between the interiors of two contiguous cells. Also known as cell-to-cell channels.

Answer 42

Gap junction (cell-to-cell channel)

Question 43

A class of carriers able to transport a specific species in either direction governed only by concentrations of that species on either side of the membrane.

Answer 43

Uniporter

Question 44

a region of ion channel proteins that determines the specificity of a particular channel.

Answer 44

Selectivity filter

Question 45

A transmembrane channel that is opened by membrane depolarization; the sodium and potassium channels of axon membranes are good examples.

Answer 45

Voltage-gated channel

Question 46

A genetic disorder in which the recovery of the action potential from its peak potential to the resting equilibrium potential is delayed.

Answer 46

Long QT syndrome (LQTS)