Module 1 Lecture 8: Assisted Membrane Transport Flashcards
Carrier-mediated transport has two forms of transport. What are they?
Passive and Active
How is active transport of carrier-mediated different from passive transport?
Requires to use of ATP (either directly or indirectly)
What is unique about Primary Active Transport?
1) Uses ATP directly to help substances against their concentration gradients
2) Carrier proteins binding sites have a greater affinity for the ion on the lower concentration side
What’s true about binding affinity and lower concentration?
The lower the concentration gradient the higher the binding affinity
What are the primary active transport carriers also known as and why?
Known as pumps because they act as enzymes with ATPase activity
What are the two types of pumps that always transport ions?
Single passenger pump (H+ or Ca2+) or a pump that transfers two substances in the same or different directions (Na+ – K+ pump)
What does the ATPase do?
Cleaves P from ATP and uses it to change the conformational shape of the protein to make it force the molecule in the carrier out the high-concentration side
Explain how this pump works to transfer ions?
1) The pump has three affinity sites for Na+ and two low affinity for K+ because the carrier protein is facing the ICF
2) When three Na+ ions bind to high affinity site it causes ATP to split into ADP and the phosphate binds to the pump
3) This phosphorylation causes the pump to flip-flop (conformational change) and face to ECF where the high concentration of sodium ions are and become released
4) Now that the pump faces the ECF it has a high affinity for K+ and it binds 2 ions to it’s binding sites
5) Once the K+ ions bind, the phosphate group is released and this causes another conformational change (original position)
6) K+ ions face the ICF where the concentration is higher and is then released into which also means the Na+ affinity is higher now going back to step 1.
How does Primary Active Transport set up Secondary Active Transport?
Helps establish Na+ and K+ concentration gradient across the membrane and indirectly serves as an energy source for S.A.T
What are unique features of Secondary Active Transport?
1) Requires energy but not directly from ATP
2) Uses second hand energy in the form of the ion concentration gradients from Primary A.T.
How does Secondary Transport work?
Due to the electrochemical gradient Primary Active Transport made with the Na+ and K+ ions the molecules use the gradient of Na+ and K+ ions that are going to go back (high to low concentration); piggy back on the gradients of the ions
What is Symport and Antiport?
Symport (cotransport) uses a ion moving down it’s concentration gradient (Na+) to also move in the same direction from low concentration to high concentration for that solute
Antiport (counter-transport): a solute that uses the concentration gradient of an ion moving from high concentration to low concentration to move through the membrane in opposite directions
How exactly is Symport and Antiport using ATP indirectly?
The sodium and potassium concentration gradients used ATP to help transfer the ions from low to high concentration. Now that the ions decide they want to go back, these other molecules can go along because they are hitching a ride with these molecules that used energy; hence indirect use of energy
