all right Welcome to our third and final video for chapter five in this video we're going to be looking at active transport including bulk transport so active transport is pretty much the opposite of passive transport in this case we're going against the concentration gradient moving something from low to high concentration it always has to involve a protein so unlike simple diffusion where molecules could pass directly through the cell membrane this is not the case for active transport Transporters are always necessary so besides going against the concentration gradient the molecule can also be going against its electrochemical gradient for example if I wanted to move protons or these hydrogen ions toward a solution that is already more positive it would take work to do so you're going against its electrochemical gradient and energy is always needed for active transport remember for passive transport no energy was needed for those three types diffusion facilitated diffusion or osmosis for active transport we have two types primary active transport is when ATP is used directly to provide the energy to move something from a low to high concentration gradient or against its electrochemical gradient and secondary active transport occurs where you're not using ATP directly but you need an electrochemical gradient or a concentration gradient that was provided by the primary active transporter so secondary active transport depends on the existence of primary active transport where do electrochemical gradients come from they really come from a combination of concentration gradients of different ions inside and outside of the cell as well as electrical gradients so what happens inside the cell so if I look the right side is the inside of the cell the cytoplasm the left side is the outside fluid or extracellular fluid it just so happens that we have DNA proteins organelles inside of the cell and the net charge of all of those things is negative they're negatively charged on the outside of the cell we primarily have sodium and chloride we have other molecules too but not as many as you find inside of the cell we'll also see that we have Transporters that are going to leave the inside of the cell with a net negative charge an important type of electrochemical gradient in our cells is produced by something called the sodium potassium pump sometimes this is called the sodium potassium ATP Ace it's a pump that uses ATP so the sodium potassium pump pushes three sodiums out of the cell and two potassiums into the cell and it uses one ATP to do so what this does overall is causes a net negative charge inside of the cell because you're pushing three positive ions out but only taking two positive ions in and this is one of the reasons we have this net negative interior charge of the cell and in our book it says this question is posed injecting a potassium solution into a person's blood is lethal and this is how capital punishment and euthanasian subjects die so why do we think a potassium solution injection can be lethal so for this concentration gradient that's shown here this is what's normally found in all of our cells and cells usually have a high concentration of potassium inside the cytoplasm whereas the outside is high in sodium what happens if we inject potassium into the blood is that the concentration of potassium will increase and this messes up the signal that our heart needs to contract our heart usually needs this nice balance of sodium on the outside in potassium or more potassium on the inside to contract properly if you have an equal concentration of potassium inside and outside the heart will stop beating and potassium actually is also used and injected during surgery to stop the heart if needed so carrier proteins are always needed for active transport and we have three types these are going to be transmembrane and integral carrier proteins sometimes we call them pumps so of our three types A unit Porter carries just one molecular ion into or out of the cell quarters carry two different molecules both in the same direction either into or out of the cell at the same time in antiporters move two different molecules in two different directions as I can see a is going one way B is going the other way our first type primary active transport involves the direct use of ATP to move something against its concentration gradient here we're using the word up this is against the most popular example in biology is the sodium potassium pump where we're moving three sodium molecules out of the cell and this is against its concentration gradient because there's already a greater concentration of sodium outside of the cell at the same time this pump also moves two potassium into the cell which is also against its concentration gradient because there's already more potassium inside the cell and it involves a direct use of ATP in our book it tells us the specific steps and their order don't worry about it this is what I want you to know for now three sodium out two potassium in both against their concentration gradients and a direct use of one ATP molecule for this ratio of ions so what do you guys think is this pump a uniporter supporter or antiporter also this pump is also known as an electrogenic pump why do you guys think it's called an electrogenic pump if you want to try it pause the video really quick and then I'll tell you the answer in a second all right so what do you guys think you're moving something in and something out I should have underlined this first but this one two opposite directions this must be an anti-porter what about this term electrogenic this pump is called an electrogenic pump because it creates a charge imbalance three positive ions out two positive ions in we see a net negative charge on the inside so there's an electrical imbalance created by this pump and that contributes to something we call the membrane potential you'll see if you take physiology or bio4b secondary active transport does not use ATP directly but it relies on the electrical chemical gradient that was created by the primary active transporter so in this case we set up using the primary active transport we set up a concentration gradient previously where there was more sodium on the outside of the cell and less sodium inside of the cell now in secondary active transport we're going to use that electrochemical gradient we set up earlier if we allow sodium back into the cell that is a favorable reaction and that reaction will release energy that energy can be used to power the movement of a nullar molecule another molecule against its concentration gradient so in secondary active transport we're allowing the molecule sodium for example one molecule down its concentration gradient which releases energy that powers an unfavorable reaction moving something against its concentration gradient here this looks like a sodium glucose transporter sodium is going down its concentration gradient which is favorable glucose is being moved against its concentration gradient with which is unfavorable so many amino acids also move in this way so why is this called active transport if ATP is not involved again this is because we rely on what the primary active transporter which did use ATP what it already did we can't we cannot have secondary active transport without what the role of the primary active transporter already completed here's a nice example of something that has both primary active transport and secondary active transport so here I can see if I Orient myself this is the inside of the cell here's the outside and here I see my primary active transporter I'm moving protons out of the cell and that looks like it's against the concentration gradient so I know that takes work to go from low to high concentration and that is is being provided by ATP so energy is being provided by ATP now that I've built this nice concentration gradient where there's more protons on the outside I can allow protons to come back in which is a favorable reaction and I allow that and capture that energy energy by pushing sucrose against its concentration gradient so this must be my secondary active transporter the last section of chapter 5 in our textbook talks about bulk transport so bulk transport is what it sounds like sometimes we have molecules that are too big to pass through even a transport protein or we need to move a bunch of stuff into or out of the cell at the same time energy is always required in bulk transport so this is a type of active transport so there are two types of movements moving things into the cell is known as endocytosis moving things out of the cell exporting stuff is called exocytosis so let's look at endocytosis first taking things into the cell there are three types we have phagocytosis also known as cell eating pinocytosis also known as cell drinking and receptor mediated endocytosis where something has to bind to a receptor on our cell before we take it into the cell here's a nice picture showing endocytosis our first type phagocytosis which is also known as cell eating the cell membrane invaginates and takes in the particle or sometimes this is even a bacterium if this is a white blood cell and creates a vesicle or vacuole housing the bacterium or particle of Interest often what happens next is this fuses with a lysosome remember these are digestive organelles that will release digestive enzymes and can cause degradation of whatever we just took in in our second type pinocytosis this is also known as cell drinking the cell membrane also invaginates and we're often taking solutes a bunch of solutes into the cell in our third type of endocytosis receptor-mediated endocytosis uptake of the molecular molecules can only happen once the molecules bind to a receptor located on the surface of the cell in this case the inner portion or the interface of the membrane is usually bound with clathrin proteins to stabilize that portion of the cell membrane the compound binds to the receptor and causes the cell membrane to evaginate and take in the molecules through receptor-mediated endocytosis there are some diseases where this invagination and uptake is not working properly and one example that's fairly common is a genetic disorder known as familial hypercholesterolemia so this is inherited and what happens in this case is that individuals with familial hypercholesterolemia have defective LDL receptors on their cells LDL is known as bad cholesterol and in people without working LDL receptors LDL is not lowered the concentration of LDL is not lowered in the blood LDL stays high in the blood which can cause dangerous problems in terms of blood vessel and heart disease finally our last type of bulk transport is in the opposite direction here we're looking at exocytosis in exocytosis we have vesicles whose membrane will fuse with our cell membrane releasing the contents into the extracellular space and then the membrane you can see stays part of becomes part of the cell membrane this takes us to the end of chapter five in chapter 6 the next chapter will be exploring metabolism energy and enzymes