Talbot - Crossing the membrane: Protein Mediated Transport Flashcards Preview

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Flashcards in Talbot - Crossing the membrane: Protein Mediated Transport Deck (54):

what are the 2 categories of protein-mediated transports

carriers and channels


what happens to the solute in a carrier

after the solute binds to the protein it causes it to change conformation in order to move the solute


what happens to the solute in a channel

it moves through aqueous pose in membrane and only interacts weakly with channel proteins


what route is faster/more efficient in moving solutes

channels - they do not have to open each time a solute comes along


what are the 3 types of carriers

uniport, symport and antiport


what kind of transport is a uniport

transports 1 solute - either facilitated or primary active transport


what kind of transport is a symport

2+ solutes in the same direction - coupled transport (primary or secondary active transport)


what kind of transport is a antiport

2+ solutes in opposite directions - coupled transport (primary or secondary transport)


what type of pump has "ATPase or pump" in the name

active transport


what are the 3 types of "solute carrier superfamily"

they do not hydrolyze ATP or couple to an electron transport chain - transporter, cotransporter, and exchanger


what does a transporter do

same as uniporter


what does a cotransporter do

same as symporter: solutes are going in same direction (primarily into cell) and usually has a / between solutes in name


what does an exchanger do

same as antiport: usually has a - between solutes in name


what is the 4th helix involved with in the ion channels

sensing actual membrane potential (voltage sensors)


what is the 6th helix involved in the ion channels

may line the transmembrane pore


what are the 4 types of ion channel gates

1. ligand gated
2. phosphorylation gated
3. voltage gated
4. mechanically gated


how does a ligand gated channel work

(ligand = signal molecule) either a neurotransmitter or hormone that binds non-covalently to receptor domain


how does a phosphorylation gated channel work

channel is phosphorylated and remains open as long as PO4- group is attached


how does a voltage gated channel work

change in membrane potential opens gate (excitable cells like neurons and muscle fibers)


how does a mechanically gated channel work

by stretching or pressure


what is passive transport

solute moves down its (electro) chemical gradient (ex. channels and carriers)


what is primary active transport

uses cellular energy (ATP) to drive solutes against (electro) chemical gradient (ex. uniports or coupled transport, "pumps/ARPases)


how does the primary active transport get ATP for energy

transport protein directly hydrolyzes ATP for energy


what are 3 classes of transport ATPases

P-Type, F-Type (related V-type), and ABC transporters


Will a drug that inhibits ATP production affect secondary active trasnport

yes - it will first inhibit primary active transport and then inhibit secondary by stopping the potential gradient across membrane from changing


how many Na+ and K+ are transported in a Na+/K+ ATPase pump antiport

3 Na+ out of cell and 2 K+ into cell


what type of drug blocks a Na+/K+ ATPase pump

ouabain and other cardiac glycosaides


what is secondary active transport

uses potential energy stored in ion gradient to drive active transport of a different solute


what type of transporter is secondary active transport

always coupled transporters (non-ATP driven) -> cotransporters or exchangers (symport or antiport)


what is the P-type of ATPase pumps

pumps proteins that are phosphorylated by autophosphorylation of transport protein (induces a conformational change)


what are some examples of a P-type pump

cation pumps, phospholipid flippases, Na+/K+ ATPase, SERCA (sarco-endoplasmic reticulum Ca++ pump)


what is the F-type pump

transports protons- ATP synthase is used to generate ATP energy from moving proton across inner mitochondrial membrane


which direction do the F-type proton pumps work

backwards and function as ATP synthases


where are the V-type pumps found

(vacular) in organelle membranes: some epithelia and lysosomes


how do V-type pumps work

use ATP to pump H+ against its gradient


what are ABC transporter pumps

ATP-binding cassette transporters - to pump solutes other than ions out of cytoplasm


how do ABC transporters work

have 2 ATP binding domains - ATP binding and hydrolysis induces conformational changes


what are membrane domains

specific proteins that allow region of cell to have a unique function


how many domains do epithelial cells have

2 distinct membrane domains that contain proteins specific to given roles "polarized cells"


what are the 2 membrane domains of the epithelial cell

apical/luminal/mucosal membrane and basolateral membrane


how does an epithelial cell absorb sodium

epithelial Na channels (ENaC) in apical membrane allow Na+ to enter and Na/K ATPase completes in basolateral membrane complete transepithelial sodium flux, also has a K+ channel to recycle K+


how does an epithelial cell absorb NaCl

there is a Na/H exchanger (NHE) and anion exchanger (AE) on apical membrane that exchange Cl- for HCO3- and a basolateral KCC to transport Cl- out of cell


how does an epithelial cell absorb glucose

it moves across cell coupled with sodium (secondary active transport) and basolateral membrane has a glucose uniport for facilitated diffusion out of cell


how does an epithelial cell secrete chloride

NKCC secondarily actively transports chlorine into cell on basolateral membrane and CFTR (Cl- channel in apical membrane) for movement out of cell


where are tight junctions located in epithelial cells

separating the apical and basolateral membranes


what is the function of the tight junctions

prevent/minimize paracellular movement of solutes and maintain polarity of the cell


where are gap junctions in epithelial cells

connect cytoplasm between adjacent cells and allows direct communication


what makes up the structure of a gap junction

6 connexins = 1 connexon (the actual pore structure) then the connexons line up into channels


what are 2 ways water can move through a cell

both passive: simple diffusion or AQP (aquaporin) channels


what is acute hypertonicity

cells shrink in a hypertonic environment (water loss)


what does shrinkage of the cell induce

a regulatory volume increase (RVI)


what 2 things are stimulated in a hypertonic environment

NKCC and Na/H (NHE) exchange are stimulated = bringing Na, K, and Cl into cell and alkalize the pH


what does swelling of the cell induce

a regulatory volume decrease (RVD)


what channels are stimulated in a hypotonic environment

K+ and Cl- are opened and in some cases KCC cotransporter will transport Cl- out of cell with K+ have H2O follow