Carrier Proteins- Lecture 15 Flashcards
What is the difference between pumps and transporters?
pumps use ATP hydrolysis as energy sources whereas transporters use gradients as energy sources
What are the classes of pumps?
P-class, V/F class, and ABC class (ATP binding cassett)
What are examples of P-class pumps?
Na/K ATPase and SERCA
What is primary active transport?
solute that is moved against its gradient has a binding site on a pump which directly carries it through the membrane
What is secondary active transport?
the pump does not participate directly in moving the solute, but rather establishes a large gradient for another solute (often NA+) across the membrane, which makes it available to be harnessed by transporters that do move the solute
Where can Na+/K+ ATPase be found?
everywhere- it is ubiquitous to all cell membranes
What is a Na/K+ ATPase?
pump that uses about 40% of the cell’s ATP to remove 3 Na+ ions from the cell and bring in 2K+ ions per ATP; establishes steep gradients for Na+ and K+ across membrane that can be exploited to do work for the cell
How does Na/K+ ATPase work?
three Na+ ions bind the high affinity sites accessible from the cytoplasm (while two low-affinity sites for K+ remain unoccupied) –> ATP binds to the pump and is hydrolized by the ATPase activity –> aspartate residue on the cytoplasmic side is phosphorylated –> pump undergoes conformational change –> Na+ ions move to low affinity sites exposed to the extracellular space and release –> 3 Na+ diffuse away and two K+ ions bind to the now high affinity sites on the intracellular side –> hydrolysis of the aspartyl-phosphate bond –> conformational change back to original state, releasing K+ ions into the extracellular space
What is a SERCA pump?
pump that removes Ca2+ from the cytoplasm and sequesters it into the intracellular storage organelles (sarcoplasmic and endoplasmic reticulum)
How does a SERCA pump function?
the same as a Na/K+ ATPase but with Ca2+ going in and protons going out
What are V/F class pumps?
contribute to the acidification of organelles such as lysosomes by pumping protons from the cytoplasm to the lumen of the organelle
What are ABC class pumps?
bind ATP through ATP binding cassettes which changes the conformation of the active site so that ATP is hydrolyzed to ADP to pump uncharged or hydrophobic particles
What are examples of ABC class pumps?
Multi-drug resistance (MDR) proteins and cystic fibrosis transmembrane regulator (CFTR)
What is a uniporter?
transporters that conduct a single species of molecule down its gradient (facilitated diffusion)
What is a co-transporters?
transporters that couple the thermodynamically favorable movement of one type of molecule to the unfavorable movement of another (secondary active transport); can be symporters (move in the same direction) or exchangers/antiporters (move in opposite directions)
