Sentence stringlengths 158 2.09k | video_title stringlengths 11 104 |
|---|---|
And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that c... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy.mp3 |
And I have some pictures of cells here. This picture right over here, this picture of Pseudomonas bacteria, each of these pill-shaped things, this is a bacterial cell. And just to get a sense of scale, the width of this pill is around one micrometer. So this is approximately one micrometer, which is the same thing as o... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So this is approximately one micrometer, which is the same thing as one millionth of a meter, or you could think of it as one thousandth of a millimeter, whatever helps you conceptualize this better. And then the length here, this is about five micrometers. This is approximately five micrometers. Now over here, I have ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Now over here, I have some pictures of cells that you would find in the human body. These are red blood cells. These have a diameter of about seven micrometers. You see a similar scale for these white blood cells or some other things in here. Over here, we see a human sperm cell about to penetrate a human egg cell. And... | Cell size Structure of a cell Biology Khan Academy.mp3 |
You see a similar scale for these white blood cells or some other things in here. Over here, we see a human sperm cell about to penetrate a human egg cell. And human egg cells are some of the largest cells you'd find, especially if we're talking about spherical cells. And this cell here, this is going to have a diamete... | Cell size Structure of a cell Biology Khan Academy.mp3 |
And this cell here, this is going to have a diameter on the order of 100 micrometers. So the first question we would, and it's kind of neat that all of these pictures are almost on the same scale, so you can almost compare them. But the first question we ask is, well, how small can a cell get? Well, if you think about ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Well, if you think about it, a cell is a living thing. It's actually quite complex. It has to have information, it has DNA, it has to be able to replicate itself. It has all of this metabolic machinery. So I just did some reading, and the smallest cells observed, and I think this might be the smallest cells period, alt... | Cell size Structure of a cell Biology Khan Academy.mp3 |
It has all of this metabolic machinery. So I just did some reading, and the smallest cells observed, and I think this might be the smallest cells period, although there might be future ones that are discovered that are even smaller, are actually on the order of about a few hundred nanometers. Remember, a thousand nanom... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So a few hundred nanometers, like maybe something like that, would be maybe 300 nanometers. These were the smallest cells discovered so far. They were bacterial cells. They were discovered at the University of California, Berkeley. And we think that this is pretty close to the lower bound, because you've got to remembe... | Cell size Structure of a cell Biology Khan Academy.mp3 |
They were discovered at the University of California, Berkeley. And we think that this is pretty close to the lower bound, because you've got to remember, we have to store all of this genetic information and all of this cellular machinery. So that stuff's complex, and you can only get so small. But what about the upper... | Cell size Structure of a cell Biology Khan Academy.mp3 |
But what about the upper bound of cells? Well, one of the things that tends to be the limiting factor, and there's other things as well, but it's the ability for, it's the ratio of volume to surface area. And why does volume, why does that, why does the ratio of volume to surface area matter? Well, because the surface ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Well, because the surface is what interfaces the cell with its surroundings. It has to take in nutrients and take out the waste. So each unit of surface area, it has to process the inputs and the outputs for a certain volume of cells, or for a certain volume of the cell. And as we'll see as the cell grows, the volume a... | Cell size Structure of a cell Biology Khan Academy.mp3 |
And as we'll see as the cell grows, the volume and surface area don't grow together. The volume increases faster than the surface area does. So as you grow, each unit of surface area has to handle the processing with the environment for more and more volume. At some point, it just can't handle it. It can't take in nutr... | Cell size Structure of a cell Biology Khan Academy.mp3 |
At some point, it just can't handle it. It can't take in nutrients and get rid of waste fast enough. And to make that a little bit more tangible, let's think about it mathematically. So the volume, the volume of a sphere, let's say this is a sphere here, so let me make it look a little bit more three-dimensional. If it... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So the volume, the volume of a sphere, let's say this is a sphere here, so let me make it look a little bit more three-dimensional. If it has radius r, its volume is going to be 4 3rds pi r cubed. Now its surface area is going to be, its surface area is going to be 4 pi r squared. Now let's calculate the ratio of volum... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Now let's calculate the ratio of volume to surface area, because that's what we really care about, the ratio of volume to surface area is, I want to do surface area in yellow, to surface area is equal to, it's equal to 4 3rds pi r cubed over 4 pi r squared. Now luckily, this simplifies quite nicely. 4 divided by 4 is 1... | Cell size Structure of a cell Biology Khan Academy.mp3 |
And if we wanted to care about units, it would be cubic units of volume, or it would be cubic units divided by square units, whichever unit we're looking at. So this is going to be r over 3. So let's use this to think about what happens as a cell gets much larger. So for simplicity, let's focus on this white blood cell... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So for simplicity, let's focus on this white blood cell here, and just to make the math easy, let's assume that it has a radius, let's assume it has a radius of 3 micrometers. I'm going to do this in a color you can see. 3 micrometers. So in that case, for this cell, its volume to surface area is going to be 3, we coul... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So in that case, for this cell, its volume to surface area is going to be 3, we could just say 3 micrometers divided by 3, but I'll put 3, we could say 3 micrometers divided by 3, which of course is just going to be 1 micrometer. But having a unit of 1 micrometer for volume to surface area doesn't really make a lot of ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Now obviously if you let the units cancel, you did the dimensional analysis, you'd be just left with this micrometer. But this helps us conceptualize it a little bit more, because it says that each square micrometer needs to handle 1 cubic micrometer of cellular volume. So each square micrometer, so square micrometer f... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Alright, that seems reasonable, and that's a reasonable size for a cell. But what if we were to increase things by a factor of 1,000? Or increase the radius by a factor of 1,000? And I'm obviously not drawing this to scale, but let's say we find some new organism or we theorize some organism that's cellular radius, ins... | Cell size Structure of a cell Biology Khan Academy.mp3 |
And I'm obviously not drawing this to scale, but let's say we find some new organism or we theorize some organism that's cellular radius, instead of it being three micrometers, so this was three micrometers, it's 3,000. 3,000 millionths of a meter. And just to be clear, this isn't ginormous by our scales, this would be... | Cell size Structure of a cell Biology Khan Academy.mp3 |
This would be three millimeters, it would be visible by the human eye, the kind of threshold of what the human eye can see is about a tenth of a millimeter, which is 100 micrometers. This is approximately, or this is one tenth of a millimeter. So in the right conditions, you could just barely see a human egg cell. But ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
But this right over here, this would be still small by our scales, but let's just think about what happens to the volume to surface area. Volume to surface area, 3,000 micrometers divided by three, 3,000 micrometers divided by three, we'd be left with, this is 1,000 micrometers, or even better, we could write this as 1... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So it has to handle much more volume. And that's gonna break down. It's not gonna be able to exchange the gases, exchange the nutrients, exchange the waste fast enough for this cell to function. So this is a very important ratio, volume to surface area for cells. And it actually ends up, well, I'll just talk about cell... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So this is a very important ratio, volume to surface area for cells. And it actually ends up, well, I'll just talk about cells in general. It actually tends to be an interesting thing as a lot of things grow, volume to surface area or mass, or, well, there's a lot of other ratios that are interesting, but this is one o... | Cell size Structure of a cell Biology Khan Academy.mp3 |
Now the other factor that will play in is also as the cell gets larger, the machinery has to just traverse more distances. You have to transport things over longer distances, which also can become cumbersome. But the volume to surface area is a really interesting one to think about why we don't tend to see very, very, ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
And the reason why I emphasize spherical cells is because you do see cells that are longer than even this scale, like nerve cells. And they get by with that. They have other adaptations, but one of them is to just be really skinny and long. So this is one way that they can maximize their surface area. So like that, thi... | Cell size Structure of a cell Biology Khan Academy.mp3 |
So this is one way that they can maximize their surface area. So like that, this is a nerve cell. Other ways that you'll see cells that maximize their surface area is that they have a lot of things that kind of stick out to maximize. So cells are clearly not all spherical. So they could have other things that maximize ... | Cell size Structure of a cell Biology Khan Academy.mp3 |
You can see his name on his patch right over there. And then this is Scott Kelly. And the reason why we want to look at these two astronauts in particular is to think about genotype and phenotype that we have been introduced to in other videos. So just as a bit of a review, when people talk about genotype, they're talk... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
So just as a bit of a review, when people talk about genotype, they're talking about the actual genetic information encoded in an organism's genes. So if you go inside a cell, we have chromosomes, and then on those chromosomes, each chromosome's a long stretch of DNA, and then sections of that long stretch of DNA will ... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
The observable characteristics, that is phenotype. And two people with the same genotype, they might have a very similar phenotype, but they won't necessarily have an identical phenotype because above and beyond the genes affecting phenotype, you also have the environment affecting someone's phenotype. So as you can se... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
They have the same genotype. But if you just look at their facial characteristics, you can see that you could tell the difference between the two. And it's not just the fact that Mark has a mustache and that Scott doesn't. We could draw in a mustache. You would still see that they look different. And that's because the... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
We could draw in a mustache. You would still see that they look different. And that's because their bodies developed in different ways based on the environment that they happen to be in. And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity. Phenotype. Pheno... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity. Phenotype. Phenotype plasticity. And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, Nassau was intrigued to see, well, what would happen to the gene expression if Sc... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, Nassau was intrigued to see, well, what would happen to the gene expression if Scott Kelly spent an extensive period of time in space while his twin brother didn't? So they looked at how their bodies expressed certain characteristi... | Phenotype plasticity Heredity AP Biology Khan Academy.mp3 |
So the regulation of gene expression can be modulated at virtually any step in the process, from the initiation of transcription all the way to post-translational modification of a protein, and every step in between. And it's the ability to regulate all these different steps that helps the cell to have the versatility ... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
So starting at the beginning of gene expression, let's talk about gene regulation as it pertains to DNA and chromatin regulation. Let's talk about the structure of DNA. DNA is packed into chromosomes in the form of chromatin, also known as supercoiled DNA. And so chromatin is made up of DNA, histone proteins, and non-h... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And so chromatin is made up of DNA, histone proteins, and non-histone proteins. And there are repeating units in chromatin called nucleosomes, which are made up of 146 base pairs of double-helical DNA that is wrapped around a core of eight histones. And there are four different types of histones within this structure o... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And they're named H2A, H2B, H3, and H4. That's just the nomenclature they've been given. Now, acetylation occurs at the amino terminal tails of these histone proteins by an enzyme called histone acetyltransferase, which I'll just abbreviate as HAT. And this is a reversible modification. So the acetylation of histones i... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And this is a reversible modification. So the acetylation of histones is sort of kept in balance by another enzyme that removes these acetyl groups, which is called histone deacetylase, or HDAC, HDAC. The acetylation of histones leads to uncoiling of this chromatin structure. And this allows it to be accessed by transc... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And this allows it to be accessed by transcriptional machinery for the expression of genes. On the flip side of this, histone deacetylation leads to a condensed or closed structure of the chromatin, and less transcription of those genes. When these modifications that regulate gene expression are inheritable, they are r... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
So when it comes to gene expression in DNA, you can basically think of DNA as coming in two flavors. Densely packed and transcriptionally inactive DNA, which is called heterochromatin, and then less dense transcriptionally active DNA, which is euchromatin. And I like to think of heterochromatin as being densely packed ... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
Whereas euchromatin is waiting there with open arms, welcoming the transcriptional machinery to transcribe away. Now often, you will see that histone deacetylation is combined with another type of DNA regulatory mechanism, and that is DNA methylation. And this occurs in a process called gene silencing. And this is a mo... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And this is a more permanent method of sort of down-regulating the transcription of genes. And DNA methylation involves the addition of a methyl group, which is a carbon with three hydrogens, to the cytosine DNA nucleotides by an enzyme appropriately called methyl transferase. And this typically occurs in cytosine-rich... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
Don't forget that cytosine pairs with G, guanine, so that's why there are Cg islands that you'll find. DNA methylation stably alters the expression of genes. And so it occurs as cells divide and differentiate from embryonic stem cells into specific tissues. And so this is essential for normal development and is associa... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And so this is essential for normal development and is associated with other processes such as genomic imprinting and X chromosome inactivation, topics for another discussion. And abnormal DNA methylation has been implicated in carcinogenesis, or the development of cancer. So you can see how the normal functioning of D... | DNA and chromatin regulation Biomolecules MCAT Khan Academy.mp3 |
And that's because a cell's DNA is contained in its nucleus. But there are actually a few exceptions to this general rule. So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have thei... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellula... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts. So chloroplast... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And tho... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosyn... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have to do with proteins or things that are involved in photo... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a normal cell in that organism would have, so we call that N. And then we have a sperm cell. Remember, the sperm c... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it come... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just going to scribble some blue inside. And the zygote also has those mitochondria, beca... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It does not give the zygote anything else. So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it ... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have these mitochondria, but these mitochondria came only from the egg cell. None of those mi... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the mitochondria that this organism will eventually have o... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism. And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendeli... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that comes from only one of the gametes, for example, just from the egg cell. And in fact, ev... | Extranuclear inheritance 1 Biomolecules MCAT Khan Academy (2).mp3 |
At the California Academy of Sciences, our mission is to explore, explain, and sustain tropical rainforests. Scientists, like Michelle Troutwine, are experts in these efforts, conducting research to help us better understand the structure and diversity of rainforest ecosystems. Entering a tropical rainforest, we find v... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
The forest floor receives very little sunlight. It is a hot, humid place where animals like leafcutter ants spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, you find amphibians, like the poison dart frog, whose tox... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social gro... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here, we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, r... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found in the rainforest, making it the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, ... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, community B has greater evenness, a more balanced number of individuals from e... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
We recognize community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances like defor... | Exploring Ecosystems Tropical Rainforest Diversity California Academy of Sciences (2).mp3 |
And to be more precise, meiosis I, and to be even more precise in that, prophase I. But we spent a good bit of time on prophase I because some interesting things happened. Some things happened just like prophase and mitosis, where the nuclear envelope disappears or starts to disappear. You have the chromosomes go into ... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
You have the chromosomes go into their dense form that has kind of this classic shape that you could see from a microscope. But what was unique or what was interesting about meiosis I and prophase I in particular is that you have this chromosomal crossover that it's a pretty typical thing to happen in meiosis I. And it... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
So these sections of the chromosome tend to code for the same genes. They're just different variants of those same genes. They might have different alleles. And once again, this just adds more variation as we get into sexual reproduction. So it's kind of a neat thing that happens here. But now let's continue with meios... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
And once again, this just adds more variation as we get into sexual reproduction. So it's kind of a neat thing that happens here. But now let's continue with meiosis, and in particular meiosis I. And you could guess what the next phase is going to be called. It is metaphase I. Metaphase. Metaphase I. And it has some si... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
And you could guess what the next phase is going to be called. It is metaphase I. Metaphase. Metaphase I. And it has some similarities with metaphase and mitosis. So in metaphase I, so let me draw my cell. So this is the cellular membrane right over there. I have my centrosomes, which are now going to play more signifi... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
And it has some similarities with metaphase and mitosis. So in metaphase I, so let me draw my cell. So this is the cellular membrane right over there. I have my centrosomes, which are now going to play more significant roles. The nuclear membrane is now gone. And just like in metaphase and mitosis, my chromosomes are g... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
I have my centrosomes, which are now going to play more significant roles. The nuclear membrane is now gone. And just like in metaphase and mitosis, my chromosomes are going to line up along, here I'll draw it kind of this up-down axis. So let's do that. So you have this one right over here. This is one chromosome, two... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
So let's do that. So you have this one right over here. This is one chromosome, two sister chromatids, and we had the chromosomal crossover, so it has a little bit of pink here. I'm going to have to take a little bit of time to switch colors a little bit more frequently. And then you have the one, at least most of whic... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
I'm going to have to take a little bit of time to switch colors a little bit more frequently. And then you have the one, at least most of which you got from your mother. But there's been a little bit of chromosomal crossover over here as well. So let me draw that. And then you have this one, and just for the sake of, s... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
So let me draw that. And then you have this one, and just for the sake of, so you have this one, this chromosome from your father. It has replicated, so it's now two sister chromatids. And this one from your mother. And I'm not going to show the chromosomal crossover here. Maybe it didn't happen over here. No homologou... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
And this one from your mother. And I'm not going to show the chromosomal crossover here. Maybe it didn't happen over here. No homologous recombination over here. So these are, I guess, shorter. Now let me draw the centromeres. The centromeres I've started doing in this blue color. | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
No homologous recombination over here. So these are, I guess, shorter. Now let me draw the centromeres. The centromeres I've started doing in this blue color. So the centromeres. And then the centrosomes, you have these microtubules that start, they can push the centrosomes away from each other. But they also attach at... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
The centromeres I've started doing in this blue color. So the centromeres. And then the centrosomes, you have these microtubules that start, they can push the centrosomes away from each other. But they also attach at the kinetochores to the chromosomes. Just like that. So, and these are, you know, the microtubules, you... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
But they also attach at the kinetochores to the chromosomes. Just like that. So, and these are, you know, the microtubules, you'll see people just talk about, oh, these connect and they're able to move things around. But I find this incredible. That you just have a bunch of proteins through just kind of chemical and th... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
But I find this incredible. That you just have a bunch of proteins through just kind of chemical and thermodynamic processes are able to do really interesting things like move chromosomes to different parts of the cell so that we eventually can get these gametes that can participate in sexual reproduction. This is an a... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
And, you know, it's kind of, it's developed over billions of years of evolution. But it's just mind-boggling to think about the complexity. And not all of this is completely understood exactly how all of this works. I mean, you have these kind of motor proteins that help move the chromosomes along these microtubules ca... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
I mean, you have these kind of motor proteins that help move the chromosomes along these microtubules can elongate and shorten in interesting ways. So it's a really fascinating process. But anyway, this is what's happening in metaphase one. Now you can probably guess what happens after that. We then move to anaphase on... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
Now you can probably guess what happens after that. We then move to anaphase one. So let me, we now go to anaphase one. I'll write that over here. Anaphase, anaphase one. And just like in anaphase and mitosis, over here, the chromosomes start getting pulled apart. Except for one significant difference. | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
I'll write that over here. Anaphase, anaphase one. And just like in anaphase and mitosis, over here, the chromosomes start getting pulled apart. Except for one significant difference. And this is actually a very significant difference. In mitosis, in mitosis, the sister chromatids get pulled apart. The sister chromatid... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
Except for one significant difference. And this is actually a very significant difference. In mitosis, in mitosis, the sister chromatids get pulled apart. The sister chromatids get pulled apart to become two daughter chromosomes. That does not happen in anaphase one. In anaphase one, the sister chromatids stay together... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
The sister chromatids get pulled apart to become two daughter chromosomes. That does not happen in anaphase one. In anaphase one, the sister chromatids stay together. It's the homologous pairs that get pulled apart. So let me draw that. So this homologous pair up here gets pulled apart. The two sister chromatids do not... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
It's the homologous pairs that get pulled apart. So let me draw that. So this homologous pair up here gets pulled apart. The two sister chromatids do not get pulled apart here. So you have this one is getting pulled onto this side. So this one's getting pulled onto this side. It has a little bit from the original, so a... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
The two sister chromatids do not get pulled apart here. So you have this one is getting pulled onto this side. So this one's getting pulled onto this side. It has a little bit from the original, so a little bit of that right over there. And then you have this one getting pulled on this side. So draw it the best I can. ... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
It has a little bit from the original, so a little bit of that right over there. And then you have this one getting pulled on this side. So draw it the best I can. The colors, alright, so it looks like that. Oh, it's nice to have, it's kind of easy to keep track of because these switch colors like that. And then you ha... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
The colors, alright, so it looks like that. Oh, it's nice to have, it's kind of easy to keep track of because these switch colors like that. And then you have this one getting pulled on this side. This one getting pulled on this side. And finally, finally, this one getting pulled onto that side. And let me draw the cen... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
This one getting pulled on this side. And finally, finally, this one getting pulled onto that side. And let me draw the centrosomes. So that's my, whoops, centrosome. And once again, it's pulling. It's, or I guess you could say the chromosomes being moved. And these things are pushing each other apart. | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
So that's my, whoops, centrosome. And once again, it's pulling. It's, or I guess you could say the chromosomes being moved. And these things are pushing each other apart. The two centrosomes might be pushing apart to get to the opposite ends of the actual cell. But they're bringing, there's all sorts of interesting mec... | Phases of meiosis I Cells MCAT Khan Academy.mp3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.