Block 2 Lecture 21 Flashcards
(44 cards)
what is active transport
net movement of substrate against its electrochemical gradient. to do this energy has to come from a source other than the substrates own electrochemical gradient
what are the two sources of energy for active transport
- metabolic (chemical) energy
2. gradient energy
what is metabolic (chemical) energy
energy derived from direct hydrolysis of ATP by the transport used to support primary active transport
what is gradient energy
energy obtained through dissipation of energy in the electrochemical gradient of a different substrate. used to support secondary active transport
what do ABC transporters do
primary active transporters, hydrolyze ATP to provide the energy for making substrates against their gradients
what do ABC transporters do in mammals
pump potentially toxic compounds out of cells
what do MDR transporters do
effective at clearing cells of toxic compounds they are very big proteins
what do ion pumps do
- use ATP to move Na, K, Ca and/or H ions against their electrochemical gradients
- they are saturable and selective
- their activity involved hydrolysis of ATP they are all ATPases
- they are all P-type ATPases reflecting the fact that during the overall reaction cycle the transport protein itself is transiently phosphorylated, then dephosphorylated
what are the p-type ATPases
- the Na, K ATPase
- the plasma membrane Ca-ATPase (PMCA)
- the sarco/endoplasmic reticulum Ca- ATPase (SERCA)
- the H,K ATPase
what does the plasma membrane Ca-ATPase do
- pumps Ca2+ out of the cell
- works to keep the cytoplasmic Ca2+ concentration in the vicinity of 50-100 nM
what happens when you inhibit Ca-ATPase
cytoplasmic Ca2+ will rise
what does the sarco/endoplasmic reticulum Ca-ATPase (SERCA) do
- pumps Ca2+ into the smooth ER
- Ca2+ stored in the ER can be pumped into cytoplasm then brought back into the ER by SERCA using ATP
what happens with SERCA when Ca2+ is increased
it activates a 2nd messenger cascade that influences phosphorylation which inhibits SERCA. when activated the second messenger system phosphorylates phospholamban and it relieves its inhibition of SERCA. net result is an increase in the rate of removal of Ca2+ from the cytoplasm back into the ER
what happens if SERCA is inhibited
cytoplasmic Ca2+ increases
what does the H, K-ATPase do
-pumps H+ out of some cells and K+ into the cell
where is the H, K-ATPase located
PMCA and SERCA are virtually invert cell but the H,K-ATPase is mainly in parietal cells in the stomach but is now found in kidney where it plays a role in H+ and K+ balance. in the stomach they pump H+ into lumen of the stomach
what does the Na,K-ATPase do
- pumps Na+ out and K+ in
- for both Na+ and K+ they are non equilibrium conditions so active transport must be involved
how are charges fixed with the Na,K-ATPase
cells contain concentrations of proteins and nucleic acids that display a net negative charge. the negative charges of these fixed anions are countered by mobile cationic charges from Na+ and K+
what is an inhibitor of Na pump activity
ouabain
what does the outwardly directed K+ gradient do
results in an inside negative membrane potential which influences the transmembrane transport of all inorganic and organic ions
what does the inwardly directed Na+ gradient do
plays a role in the generation of electrical action potentia in nerve cells, cardiac, and skeletal muscle
how does the Na, K pump affect cell volume
if cell is left unchecked the osmotic imbalance will cause the cell to swell and lyse, to counteract this cells extrude cations
what happens if the Na,K- ATPase is inhibited
cells swell
what is the only V-type ATPase
V-type H-ATPase
