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Now, this mechanism that I just talked about, that the molecules that cannot pass through the membrane, blocking the water molecules from going right to left, ricocheting off and maybe causing the ones that are on the right side to maybe move in this direction when they bounce into them, that's one explanation. Another... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
Regular table salt is sodium chloride. But when you put it in the water, you have sodium ions and you have chloride ions. And you have chloride ions. These are negative, so the chlorides are negative, the sodium ions are positive. And above and beyond doing some of the mechanical blockage that I just talked about, ther... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
These are negative, so the chlorides are negative, the sodium ions are positive. And above and beyond doing some of the mechanical blockage that I just talked about, there's also the idea that possibly that because they are ionic, they have charge, and water has partial charges, they also might stick to more of the wat... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
And so what do I mean by the water's going to stick to them? Well, when we think about a water molecule, it's an oxygen, and on the oxygen end you have a partially negative charge, and then you have two hydrogens. Two, excuse me, I'll write it this way. You have two hydrogens right over here. There's a partially positi... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
You have two hydrogens right over here. There's a partially positive charge. And so they're going to be, this oxygen end, away from the hydrogens, is going to be attracted to the sodium molecule, and so it's gonna be less, so if the sodium molecule can't make it through, this guy's gonna wanna stick to the sodium molec... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
And so you can kind of imagine all of these water molecules sticking to the sodium molecule, which would make it less likely that these would pass from right to left than the ones that are passing from left to right. Similarly, if you have a negatively charged ion like this, well, then you could orient the water the ot... | Osmosis Membranes and transport Biology Khan Academy.mp3 |
And it does that by pumping, actively pumping, three sodium ions out for every two potassium ions it pumps in, and that by itself, that ratio of three to two by itself doesn't establish the full resting membrane potential, but then the potassium ions are allowed to start diffusing down their concentration gradient from... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
It's more positive here than it is over here. They'd actually wanna go back. But their concentration gradient, they're gonna be bumping into the bottom of this channel more than the top, and so you're going to have a balance. They're going to start diffusing through, but you're not going to have equal concentrations be... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
They're going to start diffusing through, but you're not going to have equal concentrations because the charge is going to keep them back here. But what about the sodium ions? The sodium ions are getting more and more concentrated up here, and up here is getting more and more positive. If the sodium ions were left to t... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
If the sodium ions were left to their own devices, if there was no membrane over here, they would naturally, if we just looked at the concentration gradient, they would naturally want to diffuse down. We have a high concentration over here. We have a low concentration over there. So if there was no membrane, then they ... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
So if there was no membrane, then they would just naturally diffuse from high to low, that's their concentration gradient. And also if there was no membrane, we've already talked about it being much more positive on this side than it is on this side. Or you could say we have a positive potential difference between here... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
So the positively charged ions, like the sodiums up here, would want to go down because of their charge. And so there's two reasons why they would want to go from this side of the membrane to that side of the membrane, their concentration gradient and their charge, the electric potential. There's this potential energy ... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
And so that combined motivation for the sodium ions to go in that direction, we call that the electrochemical gradient. Electrochemical gradient. And I already said it once, but I'll say it again. It's a combination of the electric gradient and the chemical gradient. The chemical gradient, you have higher concentration... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
It's a combination of the electric gradient and the chemical gradient. The chemical gradient, you have higher concentration here, lower here, you would want to diffuse down. More things are gonna bump on this side than on this side, so you're gonna have a net flow down if you didn't have this membrane here. And then wh... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
And then when you think about the electric potential, more positive on this side than this side, so positive ions would want to go down. And so you could view this gradient as a source of potential energy. And cells, in fact, use this gradient. In fact, the sodium electrochemical gradient as a source of energy. And so ... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
In fact, the sodium electrochemical gradient as a source of energy. And so let's say that this protein right over here, this is what we're going to call a symporter. This is a symporter. And what it does is it uses the electrochemical gradient of one ion, in this case, sodium. So it uses the fact that sodium really wan... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
And what it does is it uses the electrochemical gradient of one ion, in this case, sodium. So it uses the fact that sodium really wants to go through the membrane. And it uses that energy. Imagine like water falling down a waterfall and it can turn a turbine or it can turn a water mill type of thing. And so it uses tha... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
Imagine like water falling down a waterfall and it can turn a turbine or it can turn a water mill type of thing. And so it uses that energy of the sodium flowing down its electrochemical gradient. It wants to go in this direction for two reasons, concentration and electric potential. So, or I guess you could say it's e... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
So, or I guess you could say it's electrostatic charge. And then it uses that energy to transport other things. And the most famous symporter with sodium is glucose. It's going to use that. The sodium and the glucose are going to go together. And the glucose is being transported against its concentration gradient. And ... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
It's going to use that. The sodium and the glucose are going to go together. And the glucose is being transported against its concentration gradient. And so if you're going to transport something against its concentration gradient, you're going to have to use active transport. So this concentration gradient, so let me ... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
And so if you're going to transport something against its concentration gradient, you're going to have to use active transport. So this concentration gradient, so let me be clear on glucose's concentration gradient. It looks like this. You have high concentration over here and you have low right over here. The cell mig... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
You have high concentration over here and you have low right over here. The cell might not want to waste all this glucose. It wants to get as much glucose into the cell or across the membrane as possible. And so it's going to have to do some active transport to go against its concentration gradient, to go in this direc... | Electrochemical gradients and secondary active transport Khan Academy.mp3 |
It's super valuable in biological systems to be able to take a glucose molecule and to phosphorylate it. So let's start with a glucose molecule and phosphorylate it. And the reason why is once you have this phosphate group, let me make sure I put that charge right over there, once you have this phosphate group, or once... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
The cell wants to hog as many glucose molecules as it can. When the glucose isn't charged, it's able to pass through the cellular membrane, but then once it becomes phosphorylated, it's going to stay in the cell. And glucose 6-phosphate right over here, this is a very important input to a whole series of processes insi... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
Now unfortunately, this reaction of taking glucose and phosphorylating it, it requires energy. It's endergonic. It's not going to happen spontaneously. It has a positive delta G. It is endergonic. And so you can imagine what we're going to need to make it happen. We're going to have to use the energy currency of the ce... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
It has a positive delta G. It is endergonic. And so you can imagine what we're going to need to make it happen. We're going to have to use the energy currency of the cell, our good friend ATP. And the way that we're going to make this reaction happen is we're going to couple what's essentially, you could view it as a h... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And the way that we're going to make this reaction happen is we're going to couple what's essentially, you could view it as a hydrolysis of ATP, although we won't have exactly a water molecule in the mechanism, but what's functionally the hydrolysis of ATP into ADP and a phosphate group, which is very energetically fav... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
It won't just always happen inside of an aqueous solution. It needs a little bit of activation energy or an enzyme to lower the activation energy, but the net reaction, it is exergonic. So what we can do is we can couple these two reactions. And so when we couple the two reactions, we have ATP plus glucose reacting, an... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And so when we couple the two reactions, we have ATP plus glucose reacting, and we use an enzyme, the general term for it is hexokinase, to facilitate this reaction, to lower the activation energy. It's going to yield glucose 6-phosphate and ADP. Now what's the delta G for this reaction going to be? Well, it's a couple... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
Well, it's a coupled reaction. You can view it as a combination of these two reactions. And so roughly speaking, you can say, well, let's just add the delta G's. So if you add the delta G's here, you're going to get, if you add this negative delta G, this exergonic and this positive delta G, you're going to get negativ... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
So if you add the delta G's here, you're going to get, if you add this negative delta G, this exergonic and this positive delta G, you're going to get negative 30.5 plus 13.8. That's going to be negative 16.7 kilojoules per mole. And so this coupled reaction is going to be exergonic, not quite as exergonic as a hydroly... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And so let's now look at the mechanism of how it happens. Now without an enzyme, the way that this reaction needs to occur is that you have an electron pair right over here on this hydroxyl group, that it needs to do what's called a nucleophilic attack on this phosphorus right over here. But without an enzyme, it's goi... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
It's going to have a high activation energy because it's going to be impaired by all of this negative charge from these oxygens right over here. You can imagine, electrons don't like going through a lot of negative charge. They're repulsed by negative charge. So we're going to need an enzyme to help facilitate this rea... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
So we're going to need an enzyme to help facilitate this reaction, to help lower the energy to actually start, and essentially get these electrons out of the way. And the enzyme, or the general term for the enzymes that do this, is called hexokinase. And hexokinase, let me write this down, and the way it does is it pro... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And in particular, it has a magnesium ion right over here, and this is bound to the rest of the hexokinase. Remember, this is all happening in three dimensions, so the hexokinase is kind of wrapping around it. So these can keep these electrons busy. There's other ions on the hexokinase that can keep these electrons bus... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
There's other ions on the hexokinase that can keep these electrons busy. Other positive ions keep these electrons busy. And so these electrons can sneak in and do the nucleophilic attack. And remember, when we talk about enzymes, these are these protein, let me do it in the same color that I wrote the hexokinase in. Th... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And remember, when we talk about enzymes, these are these protein, let me do it in the same color that I wrote the hexokinase in. These are these complex protein structures right over here, just like this. And so you might have the magnesium ion, let me do that in that purple color, just right over there, and then mayb... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And I'm obviously, I'm just kind of giving you an example. This isn't exactly what's happening. But by essentially wrapping it with this positive charge, it's able to pull the electrons away to help facilitate this nucleophilic attack that needs to happen for the reaction to proceed. And so this bond right over here be... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And so this bond right over here between this oxygen and this phosphorus, that is going to be this bond right over here. And as this happens, then these two electrons can be taken by this character. And so this oxygen is this oxygen right over here and now has a negative charge. And so what we've just resulted with is ... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And so what we've just resulted with is glucose 6-phosphate and ADP. And it's energetically favorable. It's exergonic. It's going to happen, assuming that you have the enzyme there to help distract these electrons, lowering the activation energy. And I know what you're thinking. We had this hydrogen right over here, so... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
It's going to happen, assuming that you have the enzyme there to help distract these electrons, lowering the activation energy. And I know what you're thinking. We had this hydrogen right over here, so this hydrogen should be right over here still. And then another water molecule could come and nab the hydrogen proton,... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And then another water molecule could come and nab the hydrogen proton, and so you're left once again with just the glucose 6-phosphate. So this hopefully gives you a sense of how reaction coupling occurs and also a sense of how ATP is actually useful. When I first learned about ATP, I'm like, okay, fine. It really wan... | Reaction coupling to create glucose 6 phosphate Biology Khan Academy.mp3 |
And so what's happening here is if you were in the unfortunate situation, this is not something that you would wish on anyone, if they were to have the cholera bacteria in their gut, so let's say that this is the cholera bacteria, that cholera bacteria in your intestines will release what we can call the cholera toxin.... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
It's a protein complex with various protein subunits. It's just drawn this way so that we can think about this triangle part interacting with this receptor on the epithelial cell. And so what happens is this cholera toxin, it will interact with this ganglioside receptor. And you don't have to know the details here, rea... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And you don't have to know the details here, really just the idea of what's going on. And then once it does that, when you see these arrows on these transduction pathways, you could view it as that is going to activate the next step or sometimes you might say might promote the next step or make it more likely to happen... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
You don't have to know all the details here, but G proteins are something that you'll see in a lot of signal transduction pathways. There's not just one G protein. There's a whole family of proteins called G proteins. And you can view them as molecular switches. They can get turned on and off based on how they're inter... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And you can view them as molecular switches. They can get turned on and off based on how they're interacting with other molecules, their conformation, their shape changes. And so that might activate or deactivate them. But you can follow these arrows and you can see what eventually happens. And you don't have to know e... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
But you can follow these arrows and you can see what eventually happens. And you don't have to know every detail here. Eventually it leads to adenylate cyclase, then cyclic AMP, then the protein kinase gets involved. But the end result from this pathway is that you have these ions being released from this epithelial ce... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
But the end result from this pathway is that you have these ions being released from this epithelial cell. And with that, that causes the water to leave the cell. And that's what causes diarrhea. So the toxin gets your gut cells, gets your intestinal cells to start releasing water. So then you're going to have very, ve... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
So the toxin gets your gut cells, gets your intestinal cells to start releasing water. So then you're going to have very, very, very bad diarrhea. So that's the big picture. But now we can think about what might happen in certain situations. So if I were to ask you, let's say this epithelial cell somehow had a mutation... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
But now we can think about what might happen in certain situations. So if I were to ask you, let's say this epithelial cell somehow had a mutation so its ganglioside receptor does not interact well with the B subunit here, with the cholera toxin. What would happen then? Pause this video and try to think about that. All... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
Pause this video and try to think about that. All right, so for whatever reason, this epithelial cell had a ganglioside receptor that was a little bit different and it couldn't interact as efficiently with the cholera toxin. Well, in that situation, this activation would not be happening, or at least would not be happe... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And so someone with that type of a ganglioside receptor, there might be some other negative side effects, but they actually would not get as bad diarrhea from the cholera toxin because this whole signal transduction pathway would not be happening or would not be happening as strong. Now, on the other hand, it turns out... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And if it gets activated, then it will activate another G protein. This one is different than the one here, but it's part of that same family. And when you see this type of thing, when you see a line with this flathead instead of an arrow, that means it's inhibiting that process. So for example, this opioid receptor is... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
So for example, this opioid receptor is receptive to a molecule known as enkephalin. Once again, you don't have to know that. What you should know is that, okay, you have this molecule outside of the cell that can interact with the opioid receptor, which will then activate a G protein. And what's interesting is that th... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And what's interesting is that this G protein is actually an inhibitor of this step right over here. And so if you have cholera and the cholera toxins in your gut, but you also expose those epithelial cells to enkephalin, well, that might make the diarrhea a little bit less bad because if this gets disrupted, or at lea... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
If there was some mutation in the opioid receptor here, so it wasn't as good at binding to enkephalin, what would be the end result? So if your opioid receptor is somehow not as receptive to enkephalin, well, then enkephalin will not be as effective at being able to stop this signal transduction pathway because the enk... | Activation and inhibition of signal transduction pathways AP Biology Khan Academy.mp3 |
And the first place to start is just to remind ourselves what it means for a cell to be eukaryotic. It means that inside the cell, there are membrane-bound organelles. Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells. So you'll have you... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have so... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be ins... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-b... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to someth... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagi... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that g... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of t... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that ar... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you ca... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name. Gotta love these name... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and pa... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, ge... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the an... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big ... | Organelles in eukaryotic cells Cells High school biology Khan Academy (3).mp3 |
Like a lot of times in science, the big discoveries, the ones that really change people's thinking, aren't really taken that seriously at first. And actually Mendel's work, a lot of people either didn't take it seriously or kind of ignored it in 1866. And it wasn't until the early 1900s that people rediscovered his wor... | Boveri-Sutton Chromosome Theory.mp3 |
But let's just remind ourselves about Mendel's work. So for most of human history, we've recognized probably that, okay, it looks like animals, or not just animals, any type of living creature seems to pass on traits to their offspring. I could look at you and I'd say, oh, you know, your hair is kind of like your dad's... | Boveri-Sutton Chromosome Theory.mp3 |
Maybe your nose looks like something in between. You walk a little bit like your uncle. So we've always recognized that we pass on traits to our offspring, but we didn't really have a rigorous way of thinking about it. And we definitely didn't have any way to make predictions that were testable based on those traits. A... | Boveri-Sutton Chromosome Theory.mp3 |
And we definitely didn't have any way to make predictions that were testable based on those traits. And that's what Mendel gave us. He said, well, look, I'm observing, and he did this with pea plants, I observe these heritable factors. And there might be heritable factors on, let's say, height. If we're talking about p... | Boveri-Sutton Chromosome Theory.mp3 |
And there might be heritable factors on, let's say, height. If we're talking about plants, it would be the height of a plant. There might be heritable factors on, let's say, flower color. So, flower, flower color. And he recognized that there were different versions of those factors. And so a given plant might have one... | Boveri-Sutton Chromosome Theory.mp3 |
So, flower, flower color. And he recognized that there were different versions of those factors. And so a given plant might have one of the tall versions, so they might have a tall version for the height factor, and they might have a short version. Or they might have two talls, or they might have two shorts. Or they mi... | Boveri-Sutton Chromosome Theory.mp3 |
Or they might have two talls, or they might have two shorts. Or they might have a red factor, and they have a pink factor. Or they could have two reds, two reds, it would look like that. Or two pinks would look like that. But the important realization was that there was these versions of the factor. And today, we call ... | Boveri-Sutton Chromosome Theory.mp3 |
Or two pinks would look like that. But the important realization was that there was these versions of the factor. And today, we call these factors, we say, hey, there's a gene for height, if there is one. Or that there is a gene for flower colors, and those variations of the genes, today, we call these alleles. So we'd... | Boveri-Sutton Chromosome Theory.mp3 |
Or that there is a gene for flower colors, and those variations of the genes, today, we call these alleles. So we'd say, hey, you have the variation, you have one copy of the tall allele and one copy of the short. Let me just write it this way, let me just say these are all, these are all alleles right here. So you hav... | Boveri-Sutton Chromosome Theory.mp3 |
So you have one tall allele, one short allele. And what Mendel did is he realized, well look, these things are, he didn't know how, but these things are the things that get passed on from a parent to their offspring. And he started to describe about how they got passed on. He observed that even if you have two of these... | Boveri-Sutton Chromosome Theory.mp3 |
He observed that even if you have two of these, that they tend to segregate when you go to the next generation. And what do we mean by segregation? Or I guess we could say the law of segregation. The law of segregation. Well that means if this was, if I'm a pea plant and these are the versions that I have, to my offspr... | Boveri-Sutton Chromosome Theory.mp3 |
The law of segregation. Well that means if this was, if I'm a pea plant and these are the versions that I have, to my offspring, I might pass on an A, a capital A, the tall one, or I could pass on the lowercase a. I might pass on the tall, or I might pass on the red version of the flower color factor, or I might pass o... | Boveri-Sutton Chromosome Theory.mp3 |
So they independently assort. How this one assorts is independent of how this one assorts. So independent assortment. Independent. Independent assortment. Independent assortment. Law. | Boveri-Sutton Chromosome Theory.mp3 |
Independent. Independent assortment. Independent assortment. Law. Law of independent assortment. And he also observed that some of these versions dominate the other one. So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall. | Boveri-Sutton Chromosome Theory.mp3 |
Law. Law of independent assortment. And he also observed that some of these versions dominate the other one. So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall. And that the only way they look short is if they have two versions of the short one. A... | Boveri-Sutton Chromosome Theory.mp3 |
So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall. And that the only way they look short is if they have two versions of the short one. And so that one he described as his law of dominance. And if all of this is completely new to you, I encourage... | Boveri-Sutton Chromosome Theory.mp3 |
And if all of this is completely new to you, I encourage you to watch the videos on Mendelian genetics on Khan Academy. But this is just gonna appreciate a little bit of a historical appreciation. But as big of a deal as Mendel's work was, it's also important to realize what he didn't know. He had no idea of how this w... | Boveri-Sutton Chromosome Theory.mp3 |
He had no idea of how this was actually happening at a molecular level or at a cellular level. And it wasn't until the early 1900s that people started to have fairly robust theories of how this happens. And so in 1902 and 1903, so 1902, 1903, these two gentlemen independently start coming up with the chromosome theory ... | Boveri-Sutton Chromosome Theory.mp3 |
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