Chapter 10: Membrane Transport Flashcards
Define Flux
The rate of flow through a pathway
At equilibrium, J=?
J=0 because there is no net movement across a gradient, everything is in equilibrium
that is the chemical potential difference ?
the difference in concentrations of the substance on 2 sides of a membrane.
if the inside of the cell is negative and solute particles are moving out of the cell, the transmembrane potential will be
positive, the solute particles are moving to the positive portion of the cell
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)?
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
What kind of movements generate electrical potential difference in s membrane?
transmembrane movement of ions that generate charge difference between the inside and outside of the cell membrane.
What is non mediated transport? What kind of molecules can move via non mediated transport?
non mediated transport occurs via simple diffusion and are usually small non polar molecules like O2.
What is the driving force of non-mediated transport?
the chemical potential gradient. the substances diffuse in the direction that eliminates its concentration gradient.
What’re the two categories of mediated transport?
1) passive/facilitated diffusion
2) active transport
an ionophore is used in ____transport
facilitated diffusion transport
What’re the three main various transport proteins that are used to move ions down its electrochemical gradient (in facilitated diffusion_?
permeases
ionophores
channels
In facilitated diffusion, no atp is needed because the ions move down its electrochemical gradient in such a way that the reaction is _____
thermodynamically favorable
What’re the two main types of ionophores?
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
ionophores can be used to ____ the concentrations of ions because they permit movement down the electrochemical gradient
equilibrate.
How does the structure of valinomycin allow it to do it’s job?
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.
What’re the four main methods of gating an ion channel?
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.
T/F Permeases undergo conformational change while undergoing transport
true. permeases are essentially an enzyme, which undergo conformational changes when they bind to ions they need to transport
are permeases transmembrane proteins?
yes, they span the entire membrane
What is a permease
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.
T/F permeases can move molecules against their concentration gradient
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.
What is glut1?
a permease in the erythrocye that helps transport glucose
how many conformational states does a permease have?
2
Is Glut 1 a uniport system?
Yes, because it only moves a single molecule of glucose in or out of the cell at a time
Describe the structure of GLUT1 and why it is beneficial.
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.
What is a symport system?
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
What is an antiport system
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
If you were to plot a flux vs molecule conc. graph, a nonmediated pathway would be _____ because_____
linear because the flux of a substance is proportional to the magnitude of the concentration gradient and membrane solubility
If you were to plot a flux vs [glucose] graph, a mediated pathway would be _____ because ____
hyperbolic because flux is no longer linear, the proteins used in passive transport could be saturated, where the graph reaches the plateau.
Describe the four characteristics that distinguish mediated from non mediated transport
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.
Give an example of an antiport system
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.
What kind of system is electroneutral?
a system that creates a charge neutraliziation, example, a symport system of oppositely charged ions, or the antiport system of same-charged ions.
what is an electrogenic system?
a transport system that results in charge separation across the membrane.
Difference between primary and secondary active transport
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.
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
primary active transport
there are two subunits in Na+K+ ATPase: What’re their names and functions
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.
# of Na+ gets pumped against concentration and electrical gradients, and ____ of K+ gets pumped in against the concentration gradient
3 na+ out, and 2K+ in.
Why is Na+K+ ATPase so physiologically important?
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.
What’re the three domains that belong to the alpha subnit in Na+K+ ATPase
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
What is the specific condition to which asp can get a phosphate group attached? What does this condition suggest?
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.
Na+-Glucose transport system utilizes the concentration gradient made by Na+K+ ATPase because it undergoes _______ transport
secondary active transport
that does Na+glucose transporter do?
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.
