8/29/14 - Electrical Properties of Membranes Flashcards
How does permeability of the lipid membrane differ for different types of molecules?
Small hydrophobic molecules can pass through the bilayer unassisted. Small/large uncharged polar molecules typically need assistance in passing through. Ions cannot pass through the bilayer unassisted.
What are the major types of transport proteins?
Channel mediated proteins and transporter mediated proteins
What percentage of all membrane proteins are transport proteins?
15-30%
What is the difference between passive and active transport?
Passive transport relies on the diffusion of molecules along a gradient, and active transport requires energy input (ATP) to move a molecule against its gradient.
What is a combinatorial membrane gradient?
A combination of the concentration gradient and electrical gradient across a lipid membrane.
What are the 3 different types of ion channels?
- Voltage-gated
- Ligand-gated (intracellular or extracellular)
- Mechanically gated
True/False: if the membrane potential is above a certain threshold, all channels will be open
False. Channels are not simply all open or closed, the percentage of open channels increases with membrane voltage.
What mechanism do transporter proteins use to transport solutes into/out of the cell?
Conformational changes allows the exchange of material between 2 sides of the lipid membrane.
What is the difference between primary and secondary active transport?
Primary uses ATP directly, secondary uses energy stored in electrochemical gradients to power the movement of molecules.
What are the 3 different types of transport molecules? (important)
- Uniport
- Symport
- Antiport
How does a uniport molecule function?
A molecule is directly transported from one side of the lipid membrane to the other.
How does a symport molecule function?
A molecule and its co-transported ion are transported from one side of the lipid membrane to the other.
How does an antiport molecule function?
A molecule is transported from one side of the lipid membrane to the other and its co-transported ion is transported in reverse.
What is the most commonly used ion for coupled transport?
Sodium
How is glucose transported into the cell?
Active transport against its own gradient by a transporter protein powered by a sodium gradient.
What are the 3 types of ATP-driven pumps and how do they differ?
- P-type pumps are phosphorylated during ion transport.
- F/V-type pumps: F makes ATP using an electrochemical gradient, V then hydrolyzes ATP to pump H+ across membrane.
- ABC transporters pump molecules while hydrolyzing ATP.
How is a sodium gradient established and maintained?
The Na+/K+ pump uses ATP to move 3Na+ out of a cell in exchange for moving 2K+ into the cell.
How much of our energy is dedicated to maintaining a sodium gradient?
1/3
Describe the 4 steps by which the Na+/K+ pump works. (draw out? needs work) (important)
- Na+ binds, ATP hydrolyzed
- Conformational change occurs and Na+ is transferred
- K+ binds on extracellular surface following conformational change, dephosphorylation occurs.
- K+ transferred with dephosphorylation-induced conformational change.
How do ABC transporters function?
ATP hydrolysis powers a conformational change that allows small, non-ionic molecules to pass through the membrane.
ABC transporters are relevant to which two common diseases?
- Cystic fibrosis (ABC transporter can’t transport Cl- from the cell, it accumulates within)
- Malaria (ABC transporter pumps anti-malarials from the cell)
What is cystinuria?
A genetic defect in an amino acid transporter responsible for removing cystine from urine and the intenstine. Affected individuals develop cystine stones in their bladders and kidneys
How is glucose transported from the intestinal lumen into the extracellular fluid?
It passes through a sodium-glucose symport on the apical side of the epithelium against its concentration gradient. On the basal side, glucose passively diffuses out of the cell into the extracellular fluid.
Where are concentrations of Na+ and K+ highest?
Na+ is highest in extracellular environment. K+ is highest in intracellular environment.
