okay everyone welcome back um today we're going to talk about active transport and here are the objectives that we um are going to be touching on so when we talked again about transport we had passive transport and active transport passive transport was simple diffusion and facilitated diffusion and in passive transport we're moving the substance from an area of a high concentration to an area of low concentration and there's no energy investment however in active transport it's the opposite we're moving now from an area of low concentration to an area of high concentration so that is going uphill and that is going to require energy now energy investment can be either direct right and that's what primary active transport is in which you actually have atp investment or it can be indirect right we're going to call that secondary active transport and we will explain that i also want to touch upon this briefly that we can also say we have uh looking at the different types of transporters we have uniport we have simport we have antiport what are the differences in uniport you're simply moving a single molecule using the carrier protein or the transporter in symport you're moving two molecules right two different substances um and they're moving in the same direction that direction can either be this way or it can be the opposite way it does not matter as long as they're moving in the same direction we call that simport in antiport you're also moving two different substances right but they're moving in opposite directions one of them is going in and the other out or vice versa so here's a really important example of primary active transport and this may be the single most important transporter or the most transporter that we're going to be talking about over and over throughout this course the sodium potassium atpase right it's present in in every cell and its job is to maintain high sodium concentrations on the outside and high potassium concentrations on the inside what this transporter does is that it carries three sodium ions and it moves them to the outside of the cell at the same time it also carries two potassium ions and it moves it to the inside of the cell and in order to do that right because both sodiums and potassium both of them are actually going against their concentration gradients so in order to do that we actually need atp and so this transporter or this is a form of antiport now uses direct energy as you see here so it's directly using atp as you can tell from its name atpase so sodium carries a positive charge potassium carries a negative charge so what you're doing is you're carrying three positive charges to the outside and you're also moving two positive charges to the inside so the amount of electric charge that's moving is not equal right it's not equal that's why we say that this transporter is electrogenic meaning it contributes to the negative resting membrane potential because the difference between three plus and two plus right is one right and so therefore the cell is losing three positive charges but only gaining back two charges therefore the net difference is that you can also think about it as saying well the cell is gaining one negative charge every time so this atpase actually contributes to the resting membrane potential although that contribution is is kind of limited it's only about 10 percent um this transporter is super important and you can see that in in some cells like in nerve cells neurons um 60 to 70 percent of the cell's energy requirements are devoted to this pump because again maintaining the sodium and potassium concentrations is very important for this pump to work this pump is also important for controlling cell volume right cell volume um and so because although we have not talked about osmosis yet but how this works is for now you should know at least that um water follows sodium so wherever you have sodium you're gonna have more water so what this pump does is that it gets rid of sodium so what happens when you don't have enough blood to carry oxygen the result is you can't generate atp if you don't have atp what happens is that this cell this pump i'm sorry basically stops working now when this pump starts work it stops working the amount of sodium inside the cell the concentration of sodium inside the cell is going to increase now when the concentration of sodium increases water is going to start coming in because water follows sodium now what happens the cell starts to swell and eventually it bursts and dies right and that's how that's what happens in a heart attack myocardial infarction we'll talk more about that later um here's a an example of secondary active transport and the transporter shown here is the sglt or the sodium glucose linked transporter and it uses symport so what are the two substances being transferred here you have sodium being transferred and you have glucose also being transferred right but the difference is so when you're looking at so and they're going in the same direction when you're looking at sodium sodium is going from an area of high concentration to an area of low concentration so that's just direct um that's just diffusion right because it's passive it should be however when you're looking at glucose removing glucose from the outside to the inside glucose is going against its concentration gradient because the movement of glucose is this way so the yellow here is where glucose wants to go but the red arrow that i just drew is where glucose is actually going so we are going against the concentration gradient of glucose so how we're going to do that in order to do that glucose is actually going to ride along sodium so this transporter binds sodium but the transporter is not going to move unless glucose also binds so glucose just rides along freely right with sodium once all four spots are filled the transporter is going to change in shape releasing these substances to the inside of the cell so you may wonder and say okay why are we calling this secondary active transport where is the energy um coming from well the energy is coming from the sodium gradient right for this to work you need to have a sodium gradient right that allows you know sodium to that makes sodium want to come in and bind to the transporter well where does the sodium gradient come from that's an important question right the sodium gradient comes from this guy the sodium potassium pump so we're investing energy in creating the sodium gradient so where is energy coming from so the we have atp being invested in the sodium potassium pump the sodium potassium pump generates this sodium electrochemical gradient and this sodium electrochemical gradient allows this transporter to work and that's why we call it secondary active transport because it's using that gradient that we generated for sodium to move another substance from an area of low concentration to an area of high concentration the sglt1 transporter that we just talked about it's a it's present in intestinal epithelial cells right so here's sorry here is the lumen um right in the intestine in your gut here's the blood side and so this transporter pulls in sodium and glucose together right from from this end and then you can see here and then it kicks glucose out on the other end using a different type of transporter but then you can see the sodium potassium pump working constantly using atp in order to keep the sodium concentration inside low right because if you keep sodium inside low sodium keeps coming in here and if sodium keeps coming in through the sgl t1 that means glucose also keeps coming in however if we assume this guy stops working therefore the sodium concentration starts going up right because we're not kicking sodium out what's going to happen is that this transporter is going to stop that's why this is secondary active transport even though it does not directly use energy but it is dependent upon the function of a primary transporter here's another example of secondary active transport right on the left you have the sodium calcium exchanger so this is also antiport and on the right you have the sodium hydrogen exchanger where again sodium and calcium or sodium and hydrogen are moving in opposite directions thank you