Lecture 1.5: Transporters Flashcards
What are the three types of transporters?
Uniporter: transports single solutes down concentration gradient, No need for energy. Symporter transport a solute and a coupled ion down concentration gradients. The ion gradients are a source of energy. Antiporters transport molecules in opposite directions (i.e Na,K transporter). The gradients are energy sources. Symporters and antiporters are secondary active transoporters.
Explain how the SLC2 (solute carrier) superfamily transporters function in the transport of glucose.
The transporter begins in the open-out configuration. As glucose enters the pore, the transporter changes to the occluded-out configuration (glucose is now in pore - no gates are open). Transporter switches to the open-in, glucose enters cell, and the transporter goes back to the open-out configuration. The rocker-switch method allows the solute to move through the transporter. Transmembrane domains (TM) 7 and 10 are the primary contributors to gating.
How does the Na-Glucose symporter transport the ion and solute?
This symporter is part of secondary active transport. The Na+ pump generates Na+ ions for use. Low concentration of Na+ in the cell drives glucose down its concentration gradient into the cell (active transport). Then, the concentration of glucose inside the cell will be higher than its concentration outside the cell. Glucose goes down its concentration gradient (passive transoprt).
Explain how Na,+ K+ pumps work.
4 steps: 3NA+ ions bind to the binding site and it’s the third Na+ that is coupled to phosphorylation. A conformational change to the E2 state whereby the inner gate closes and the outer gate opens doe to phosphorylation. Na+ ions flow out of the cell. Lastly there is a conformational change back to the E1 state which is accompanied by phosphate release and the binding of ATP.
