ZIMA Lecture 2 (Membrane Transport) Flashcards
The barrier function of the membrane allows the cell to what?
Allows the cell to maintain concentration of solutes in the cytysol that are different from the external fluid and each of the intracellular membrane-enclosed compartments.
What are the two main classes of membrane proteins that mediate the traffic of molecules?
By generating ionic concentration differences across the lipid bilayer, cell membranes can do which three things?
- transporters (passive/active)
- channels (only passive)
By generating ionic concentration differences across the lipid bilayer, cell membranes can store energy in the form of electrochemical gradients, which drive various transport mechanisms, convey electrical signal for comunication, and produce ATP.
What two things does the rate of diffusion depend on?
Explain the general diffusion rates of small nonpolar molecules, polar uncharged molecules, and small ion.
Rate of diffusion depends on: size of the molecule and its relative solubility in oil
Small nonpolar molecules (oxygen and carbon dioxide) diffuse rapidly across a membrane.
Polar uncharged molecules can also diffuse across a lipid bilayer.
However, lipid bilayers are highly impermeable to small ions.
All membrane transport proteins are _________.
Explain the difference between ion transporters and channels.
All membrane transport proteins are multipass transmembrane proteins.
Ion channels: always passive, but highly selective ion transport. It depends on the concentration gradient of transported ion and membrane potentials-electrochemical gradient. Ions move “downhill” their concentration gradient
Transporters: can work in both ways, passive or active transport (“uphill”). Active transport (pumps) is mediated by use of energy such as ATP. This mechanism establishes ionic gradients in a living cell.
What two things combine to form a net driving force/the “electrochemical gradient”?
The concentration gradient and the electrical gradient combine to form electrochemical gradient.
Explain the kinectics of transporters.
Transporters have one or more specific binding sites for its substrate.
The membrane transport resembles an enzyme substrate reaction and can be characterized by a similar kinetic reaction with Vmax (max velocity of transport) and Km (selectivity of transport).
Explain the following types of active membrane transport: coupled transporters, ATP-driven pumps and Light-driven pumps
- Coupled transport: couple uphill transport of one solute across the memebrane to downhill transport of another
- ATP driven pump: couple uphill transport to ATP hydrolyisis
- Light-driven pumps- couple uphill transport to light energy (this really only happens in bacteria)
Explain the following types of active membrane transport: Uniporters, Symporters, and Antiporters
Uniporters: transport of single molecule from one side to the other
Symporter: transport of one molecule depends on transport of another molecule in the same direction
Antiporter: Transport of one molecule depends on transport of a second molecule in the opposite direction
Categorize the Sodium Calcium Exchanger.
The Na/Ca exchanger is an antiporter, that uses active transport, and it is also ELECTROGENIC
(electrogenic because there is a mismatch in charge distribution because you’re exchanging three sodiums for one calcium, aka 3+ for 2+)
The usual co-transporter in eukaryotes is____.
Na+ os the usual co-transporter ion in eukaryotes.
ATP-dependent Na+ pump creates the Na+ gradient. Thus, Na+ dependent transporters mediate secondary active transport, whereas ATP-dependent mediates primary active transport.
In bacteria and yeast___ is the usual co-transporter ion.
H+
What two different transport systems do eukaryotic cells use to control cytosolic pH?
- Na+/H+ exchanger (one sodium in for one proton out)
- Na+ driven Cl- HCO3-
(sodiu, and bicarb inside, HCl outside, bicarb acts like a buffer)
What will happen if the Na/K pump is inhibited?
Glucose transport will decrease
Calcium will accumulate in the cell
pH will go down (increased protons in cytosol)
RMP will become depolarized
The ____ gradient is used for active transport of glucose on apical domain of epithelial cells.
The ___ that enters the cell during transport is pumped out by the Na/K ATPase on the basal membrane (pump or antipump)
Glucose leaves the cell via _____ (______) on the basal membrane.
The Na+ gradient is used for active transport of glucose on the apical domain of epithelial cells.
The Na+ that enters the cell during transport is pumped out by the Na/K ATPase on the basal membrane (pump or antiport)
Glucose leaves the cell via uniporter (passive transport) on the basal membrane.
What creates the transcellular glucose transport in epithelial cells?
Asymmetric distribution of transporters in epithelial cells creates the transcellular glucose transprot.
