1. Describe the functional requirements of an antiporter transport protein (i.e.
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Question
1. Describe the functional requirements of an antiporter transport protein (i.e., what properties must the protein have to operate effectively?). Do antiporters represent an example of passive or active transport? Why?
2. With reference to aquaporins or the bacterial K+ channel, describe how ion channels can ensure ion specificity while maintaining relatively high flow rates?
3.K+ leak channels play an important role in re-establishing membrane potential across cell membranes. Since these channels are always open, how can the [K+] inside the cell be nearly 30X higher than the extracellular concentration at the K+ equilibrium point?
I know it there looks like a lot of questions, but out of the 30 reviews questions I have to do, these 3 have me stumped. Exam tomm morning, so would really appreciate it if someone can help me out! Thanks in advance!!
Explanation / Answer
Antiporters are proteins which transport one molecule against its electrochemical gradient by allowing another molecule to move along its electrochemical gradient. The energy gained when one molecule moves from high concentration to low concentration is used to push another molecule from low to high concentration.
Antiporters represent active transport as they transport molecules against their concentration gradients.
The K+ channel has a high specificity for K+ ions and will not allow any other ions to enter. This is achieved by a specific sequence found in the lining of the channel. When a K+ ion enters the channel it loses its water of hydration and binds to the 8 carbonyl oxygen atoms present in the channel. This binding can be done only by K+ and not by any other ions. These channels ensure high flow rates as they dont have conformational changes like carrier proteins.
The reason for the high concentration of K+ inside the cell when compared to extracellular conditions is because of a pump called Na+/K+ ATPase which transports 3 Na+ outside the cell for every 2 K+ pumped in.
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