Secondary Active Membrane Transport: Study with Video Lessons, Practice Problems & Examples

Secondary active transport relies on an electrochemical ion gradient rather than direct ATP hydrolysis, which is characteristic of primary active transport. This process co-transports two molecules: ions move down their gradient passively, while other substances, like glucose, are transported against their gradient. The energy released from the ion's movement powers the uphill transport of the other molecule. Understanding this mechanism is crucial for grasping how cells maintain homeostasis and nutrient uptake through processes like symport and antiport.

Secondary Active Membrane Transport

Hey, guys. In this video we're going to quickly revisit our map of the lesson on membrane transport. We know that we're exploring the leftmost branches first, and we've already talked about molecular transport of small molecules, including passive transport, and we're currently exploring active transport and we've already covered all of these branches here for primary active transport. And so now in our next video, we're going to explore this little branch over here for secondary active transport, and then after that, we'll talk about a very specific example of secondary active transport in the sodium glucose symporter. So I'll see you guys in our next video to talk about secondary active transport.

Secondary Active Membrane Transport

In this video, we're going to talk more details about secondary active membrane transport. And so you might recall in our previous lesson videos we briefly introduced Secondary Active Membrane Transport. And so we already have somewhat of an idea that secondary active transport is not directly driven by ATP hydrolysis like primary active transport is. Instead, secondary active transport is actually directly driven by an electrochemical ion gradient. And we'll be able to see that down below in our image when we get there.

Now, however, what's really important to note is that although secondary active transport is not directly driven by ATP hydrolysis, it is indirectly driven by ATP hydrolysis, and that's because secondary active transport is indirectly driven by primary active transport, or PAT for short here. And so the reason that secondary active transport is indirectly driven by primary active transport and by ATP hydrolysis is that electrochemical ion gradients, which secondary active transport relies heavily on, are built by primary active transport, or again, PAT here for short, for space purposes here.

During secondary active transport, what we'll see is that it's really going to co-transport 2 molecules at a time. And so ions will be transported down or with their electrochemical gradients from areas of high concentration to areas of low concentration. Whereas other molecules such as glucose, amino acids, or things of that nature, will be transported against or up their concentration gradients from areas of low concentration to areas of high concentration.

If we take a look at our example image down below of secondary active transport, what I want you guys to notice is that over here on the left-hand side, we're showing you guys primary active transport as is labeled right here. We can tell because ATP hydrolysis is directly involved with the process of transporting this molecule here against its concentration gradient, from areas of low concentration to areas of high concentration. Then notice over here on the right-hand side of our image, we're showing you guys secondary active transport. And we can tell because notice that ATP hydrolysis is not directly involved with secondary active transport. However, it is again, indirectly involved because it relies on primary active transport to build up this electrochemical ion gradient. And so this ion right here is able to diffuse across the membrane down its concentration gradient from high to low, which does not require energy. It is a passive exergonic process.

However, notice that as the red molecule is going from high to low, this other green molecule over here is being transported against its gradient from an area of low concentration to an area of high concentration. And really, this is the transport part that requires energy. And so it's the energy released from this downflow movement of the ion from high to low that is powering the uphill movement or the uphill endergonic process of powering this molecule to be transported against its concentration gradient from low to high.

We'll be able to see an example of secondary active transport in our next lesson. But for now, this here concludes our lesson on secondary active membrane transport, and we'll be able to get some practice applying these concepts in our next video. So I'll see you guys there.

Secondary Active Membrane Transport Example 1

Alright. So here we have an example problem that says the sodium potassium pump is an example of a system that uses primary active transport to set up conditions that can ultimately allow for secondary active transport. And then it says, all of the following 5 answer options down below are true except for which one. And so essentially what this problem is asking us to do is to identify the false answer option, and so I'll write that here just as a reminder.

When we take a look at option A, it says that the sodium potassium pump is an antiporter fueled by the hydrolysis of ATP. And so you might recall from our previous lesson videos that the sodium potassium pump is an example of a P-type ATPase. And because it is an ATPase, it does involve the hydrolysis of ATP. It also pumps sodium and potassium in opposite directions across the membrane, which makes it an antiporter. And so what we're saying here is that option A is a true statement. And because it's true, it's not the false answer option that we're looking for, so we can eliminate option A.

Now moving on to option B here, it says that secondary active transport of glucose into cells moves glucose against its concentration gradient. And, of course, secondary or primary active transport, because it is active and involves the use of energy in one way or another, is going to move molecules against their concentration gradients. And so this here is also going to be a true statement. And so we can mark it as true. And, again, it's not the false answer option that we're looking for, so let's eliminate option B.

Moving on to option C here, it says that the sodium potassium pump exports sodium ions to the outside of the cell, establishing a concentration gradient for sodium. And, of course, recall from our previous lesson videos on the sodium potassium pump that it does indeed export sodium ions. And the way that we remember that is that it's trying to get into club intracellular, but the bouncers are saying no. And so the Na (sodium), nah, you can't get into the cell, reminds us that it's going to be pumped to the outside of the cell. And instead, the pump K (potassium) is going to remind us that it's K⁺ that gets pumped into the cell. And so what we're saying here is that option C here is also a true statement as is written. And so because it is true, we'll mark it as true. And again, it's not the false answer option that we're looking for so we can eliminate option C.

So now we're between either option D or option E as the false answer option. And so when we take a look at option E, notice that it says secondary active transport of glucose into cells is indirectly driven by ATP hydrolysis. And of course, we know from our last lesson video that secondary active transport is not directly linked to ATP hydrolysis. However, it is indirectly linked. And so what we're saying here is that option E here is another true statement. And because it's true, again, it's not the false answer option that we're looking for, so we can eliminate option E.

And so, of course, this must mean that option D is the false answer option that we were looking for. And so, it says that K⁺ and Na⁺ (potassium and sodium) both diffuse into the cell along their concentration gradients to drive the transport of glucose. But, of course, we know that when it comes to the sodium potassium pump, that potassium and sodium are going to be pumped in opposite directions across the membrane. So they both will not be pumped into the cell. That would suggest that they're pumped in the same direction. And so option D here again is going to be the false answer option that we were looking for. And so, what we can say is that this is the answer and that concludes this practice. I'll see you guys in our next video.

Which of the following is a way in which primary and secondary active transport may work together?

• A. Primary active transport can be used to create a concentration gradient of sodium such that sodium and glucose can move into the cell together via antiport mechanism.
• B. Primary active transport is used to create ATP necessary to drive secondary active transport.
• C. Primary active transport can be used to create a concentration gradient of sodium such that sodium and glucose can move into the cell together via secondary active symport.
• D. Primary and secondary active transport always oppose each other so they never work together.

Here’s what students ask on this topic:

What is secondary active membrane transport?

Secondary active membrane transport is a type of active transport that does not directly use ATP hydrolysis. Instead, it relies on the electrochemical gradient of ions created by primary active transport. This process co-transports two molecules: one ion moves down its concentration gradient passively, releasing energy, while another molecule, such as glucose or amino acids, is transported against its concentration gradient using the energy released from the ion's movement. This mechanism is crucial for cellular functions like nutrient uptake and maintaining homeostasis.

How does secondary active transport differ from primary active transport?

Secondary active transport differs from primary active transport in its energy source. Primary active transport directly uses ATP hydrolysis to move molecules against their concentration gradients. In contrast, secondary active transport does not directly use ATP. Instead, it relies on the electrochemical gradient of ions established by primary active transport. The energy released from ions moving down their gradient powers the uphill transport of other molecules against their gradient.

What role does the electrochemical ion gradient play in secondary active transport?

The electrochemical ion gradient is crucial in secondary active transport. It is established by primary active transport, which uses ATP hydrolysis to pump ions against their concentration gradient. In secondary active transport, ions move down this gradient passively, releasing energy. This energy is then harnessed to transport another molecule against its concentration gradient. Thus, the electrochemical ion gradient indirectly drives the secondary active transport process.

Can you provide an example of secondary active transport?

An example of secondary active transport is the sodium-glucose symporter. In this system, sodium ions (Na⁺) move down their electrochemical gradient into the cell, releasing energy. This energy is used to transport glucose molecules into the cell against their concentration gradient. The sodium-glucose symporter is essential for glucose absorption in the intestines and kidneys, demonstrating how secondary active transport is vital for nutrient uptake and cellular function.

Why is ATP hydrolysis considered indirect in secondary active transport?

ATP hydrolysis is considered indirect in secondary active transport because it is not directly used to transport molecules. Instead, ATP hydrolysis occurs during primary active transport, which creates an electrochemical ion gradient. This gradient provides the energy needed for secondary active transport. Thus, while ATP hydrolysis is essential for establishing the gradient, it does not directly power the transport of molecules in secondary active transport.