Chapter 10: Membrane Transport

Question 1

Define Flux

Answer 1

The rate of flow through a pathway

Question 2

At equilibrium, J=?

Answer 2

J=0 because there is no net movement across a gradient, everything is in equilibrium

Question 3

that is the chemical potential difference ?

Answer 3

the difference in concentrations of the substance on 2 sides of a membrane.

Question 4

if the inside of the cell is negative and solute particles are moving out of the cell, the transmembrane potential will be

Answer 4

positive, the solute particles are moving to the positive portion of the cell

Question 5

If the concentration of A outside the membrane is greater than the concentration inside the membrane, the transfer of molar free energy of A from out to inside will be ______ and the net flow will be in the ____ direction because the reaction is (spontaneous or nonspontaneous)?

Answer 5

molar free energy will be negative and the net flow will be in the inward direction (greatest to least concentration) and the reaction is spontaneous

Question 6

What kind of movements generate electrical potential difference in s membrane?

Answer 6

transmembrane movement of ions that generate charge difference between the inside and outside of the cell membrane.

Question 7

What is non mediated transport? What kind of molecules can move via non mediated transport?

Answer 7

non mediated transport occurs via simple diffusion and are usually small non polar molecules like O2.

Question 8

What is the driving force of non-mediated transport?

Answer 8

the chemical potential gradient. the substances diffuse in the direction that eliminates its concentration gradient.

Question 9

What’re the two categories of mediated transport?

Answer 9

1) passive/facilitated diffusion

2) active transport

Question 10

an ionophore is used in ____transport

Answer 10

facilitated diffusion transport

Question 11

What’re the three main various transport proteins that are used to move ions down its electrochemical gradient (in facilitated diffusion_?

Answer 11

permeases
ionophores
channels

Question 12

In facilitated diffusion, no atp is needed because the ions move down its electrochemical gradient in such a way that the reaction is _____

Answer 12

thermodynamically favorable

Question 13

What’re the two main types of ionophores?

Answer 13

carrier ionophores- increase the permeabilities of membranes to their selected ion by binding it, diffusing through the membrane, and releasing it on the other side

channel forming ionophores- form transmembrane channels through which their selected ions can diffuse

Question 14

ionophores can be used to ____ the concentrations of ions because they permit movement down the electrochemical gradient

Answer 14

equilibrate.

Question 15

How does the structure of valinomycin allow it to do it’s job?

Answer 15

valinomycin is a carrier ionophore. the backbone of valinomycin contains carbonyl groups that allow stabilization of the K+ ions, while the non polar side chains of the amino acids project outwards to provide the complex with nonpolar interactions with the membrane bilayer so it can diffuse in the hydrophobic core.

Question 16

What’re the four main methods of gating an ion channel?

Answer 16

1) Mechanosensitive channels: open in response to the local deformation sin bilayer of physical stimulations
2) Ligand-Gating: open in response to an extracellular chemical stimulus, like a neurotransmitter that binds to the cell.
3) Signal-Gated channels: open via intracellular binding a Ca2+ ion or some other signalling molecule.
4) Voltage-gated channel: open in response to a change in membrane potential, like nerve pulses.

Question 17

T/F Permeases undergo conformational change while undergoing transport

Answer 17

true. permeases are essentially an enzyme, which undergo conformational changes when they bind to ions they need to transport

Question 18

are permeases transmembrane proteins?

Answer 18

yes, they span the entire membrane

Question 19

What is a permease

Answer 19

a protein involved in facilitated diffusion that spans a membrane and allows a favorable path by which specific nutrients, ions, metabolites etc may move DOWN their electrochemical gradient across a membrane.

Question 20

T/F permeases can move molecules against their concentration gradient

Answer 20

false, permeases are involved in passive mediated transport and can only be used to equilibrate molecule concentrations across a membrane since they can only move things from high to low concentrations.

Question 21

What is glut1?

Answer 21

a permease in the erythrocye that helps transport glucose

Question 22

how many conformational states does a permease have?

Answer 22

2

Question 23

Is Glut 1 a uniport system?

Answer 23

Yes, because it only moves a single molecule of glucose in or out of the cell at a time

Question 24

Describe the structure of GLUT1 and why it is beneficial.

Answer 24

Glut 1 is made of 12 alpha helices that span the entire membrane and forms a tetramer. The helices are amphipathic and group in such a way that hydrophobic AA are on the outside to allow favorable interactions with the nonpolar membrane, and the hydrophilic AA are in the inside, to allow favorabel interactions with the polar glucose molecules that it transports.

Question 25

What is a symport system?

Answer 25

involves the transport of two different molecules in the same direction. Usually, one goes against the concentration gradient and the other goes down the concentration gradient

Question 26

What is an antiport system

Answer 26

involves the transport of two different molecules in the opposite directions.Usually, one goes against the concentration gradient and the other goes down the concentration gradient

Question 27

If you were to plot a flux vs molecule conc. graph, a nonmediated pathway would be _____ because_____

Answer 27

linear because the flux of a substance is proportional to the magnitude of the concentration gradient and membrane solubility

Question 28

If you were to plot a flux vs [glucose] graph, a mediated pathway would be _____ because ____

Answer 28

hyperbolic because flux is no longer linear, the proteins used in passive transport could be saturated, where the graph reaches the plateau.

Question 29

Describe the four characteristics that distinguish mediated from non mediated transport

Answer 29

1) specificity: unlike non mediated transport where any nonpolar molecule can diffuse down a concentration gradient, facilitated diffusion proteins are more specific to what substrates they can bind and transport.
2) Saturation: nonmediated transport does not require carrier molecules. Passive diffusion/mediated transport uses proteins that have a specific work load. If the amount of molecules greatly outnumbers the amount of protein transporters, the rate of diffusion will reach a plateau. Furthermore, there are only a handful of spots where certain types of diffusion, such as glucose, can take place.
2) Competition: the transport proteins can be inhibitied and the curve will shift right in the presense of another substance.
4) inactivation: reagents that chemically modify proteins may change the transporters in such a way that decreases its effectiveness in creating a flux.

Question 30

Give an example of an antiport system

Answer 30

the bicarbonate-chloride exhanger permease.
In the tissues, HCO3-leaves the RBC via an antiport permease in to the plasma, and Cl- ions move into the RBC. In the lungs, HCO3- enters RBC via antiport system that allows HCO3- in and Cl- out. HCO3- gets concerted to CO2 to be exhaled.

Question 31

What kind of system is electroneutral?

Answer 31

a system that creates a charge neutraliziation, example, a symport system of oppositely charged ions, or the antiport system of same-charged ions.

Question 32

what is an electrogenic system?

Answer 32

a transport system that results in charge separation across the membrane.

Question 33

Difference between primary and secondary active transport

Answer 33

primary transport uses atp hydrolysis to drive a molecule up its concentration gradient, whereas secondary active transport use the concentration gradient made by the atp hydrolysis and primary active transport for another function.

Question 34

P type ATPase/Na+K+ ATPase uses _____ transport and ATP to undergo phosphorylation as they transport cations such as Na+ and K+ across a membrane

Answer 34

primary active transport

Question 35

there are two subunits in Na+K+ ATPase: What’re their names and functions

Answer 35

alpha subunit- subunit that contains the enzyme’s ATP and ion binding sites.

beta subunit: facilitates the correct insertion of the alpha subunit into the plasma membrane.

Question 36

# of Na+ gets pumped against concentration and electrical gradients, and ____ of K+ gets pumped in against the concentration gradient

Answer 36

3 na+ out, and 2K+ in.

Question 37

Why is Na+K+ ATPase so physiologically important?

Answer 37

1) helps generate membrane potential, this is critical for electrical signalling such as action potentials
2) the concentrations gradients established via the primary active transport is used by mechanisms that undergo secondary active transport
3) without functioning Na+K+ ATPase, H2O would osmotically rush in, which would cause the cells to swell and burst because there is no mechanism pushing Na+ out of the cells.

Question 38

What’re the three domains that belong to the alpha subnit in Na+K+ ATPase

Answer 38

NAP
N= the binding domain, binds ATP
A= acutor domain, participates in trasmission of conformational changes
P= phosphorylation domain, contains phosphorylatable asp residue that helps dephosphorylate ATP by taking its phosphate group

Question 39

What is the specific condition to which asp can get a phosphate group attached? What does this condition suggest?

Answer 39

phosphorylation of the asp residue will only happen in the presence of na+, and the resuting aspartyl phosphate residue is only subject to hydrolysis in the presence of K+ (returning to its normal state). this suggests that Na+K+ ATPase has 2 confomational changes with different structures, catalytic actiivies and characteristics.

Question 40

Na+-Glucose transport system utilizes the concentration gradient made by Na+K+ ATPase because it undergoes _______ transport

Answer 40

secondary active transport

Question 41

that does Na+glucose transporter do?

Answer 41

it uses the concentration gradient made by Na+K+ ATPase to drive glucose into the cell via symport with na+. Because Na+K+ ATPase drives out, Na wants to go in, and it takes glucose with it.