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Organelles in eukaryotic cells

Eukaryotic cells have membrane-bound organelles. The nucleus stores DNA. The endoplasmic reticulum and Golgi body are involved in protein maturation and transport. Mitochondria are where ATP is made. Chloroplasts carry out photosynthesis. Vacuoles are storage compartments that sequester waste and help maintain water balance. Lysosomes contain enzymes that help break down waste. Created by Sal Khan.

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  • eggleston yellow style avatar for user Junho Son
    Where does the word "Eukaryotic" and "Prokaryotic" come from?
    (29 votes)
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    • duskpin ultimate style avatar for user Asterborn
      'Pro' is a prefix which means primitive. 'Karyot' in the other hand means nucleus. That said, a Prokaryotic living is a creature which has primitive/unidentified nucleus. However, Eukaryotic means a creature which has an identifiable nucleus. I think these are from Greek, however I'm not so sure.
      (56 votes)
  • piceratops tree style avatar for user Lakshmi.manda07
    Why is there an "m" in RNA?
    (12 votes)
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  • starky sapling style avatar for user Salty
    At Sal says "You gotta love these names in Biology", but they can't just randomly name the parts of a cell based off of like something their child said randomly when they were 2 years old. So how to scientists name these cell parts off of what do they name them? E.G. Golgi Bodies
    (7 votes)
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    • duskpin ultimate style avatar for user Polina Vitić
      Sometimes the honor of naming something goes to the scientist who discovers it. Cell parts often have names which describe their function or appearance.

      For instance, when Robert Hooke discovered cells in 1665, he decided to use the term "cell" (which came from the Latin word cella meaning "small room").

      The pathologist Camillo Golgi discovered what he called the "internal reticular apparatus" in 1897. Other scientists referred to it as the Golgi apparatus, however, and eventually the name stuck.

      Golgi bodies are the only organelle named after a person!
      (29 votes)
  • purple pi teal style avatar for user Asher James
    Is the Golgi Body and Golgi apparatus the same?
    (9 votes)
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  • primosaur tree style avatar for user mriskin-kutz
    What does the smooth E.R. do, if the rough E.R. is responsible for protein synthesis?
    (4 votes)
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  • cacteye blue style avatar for user goofygoober
    Did the word photosynthesis come from something?
    (4 votes)
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  • winston baby style avatar for user Mason Smith
    Correct me if I'm wrong, but the process that a piece of DNA goes through is it first gets out of the nucleus, then it "pairs" with a ribosome, through the E.R. to turn into mRNA, and then it leaves and goes into the Golgi Apparatus/body and it "packages" the mRNA, to then after that it leaves the cell?
    (4 votes)
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    • female robot amelia style avatar for user him
      I'm sorry, but the process you described is not entirely accurate. Let me clarify the steps involved in the central dogma of molecular biology, which outlines the flow of genetic information in cells:

      1. Transcription: The process starts in the cell's nucleus. The DNA is transcribed into messenger RNA (mRNA) by an enzyme called RNA polymerase. This step involves the creation of an mRNA molecule that carries the genetic information from the DNA.

      2. mRNA Processing: The newly synthesized mRNA may undergo some modifications before leaving the nucleus. These modifications include the addition of a protective cap at the 5' end and a poly-A tail at the 3' end, as well as the removal of non-coding regions called introns.

      3. mRNA Export: The mature mRNA, after processing, exits the nucleus and moves into the cytoplasm, where it can encounter ribosomes.

      4. Translation: Ribosomes, not the mRNA itself, "pair" with the mRNA in the cytoplasm. The process of translation occurs on the ribosomes, where the mRNA's genetic code is read, and amino acids are assembled into a polypeptide chain to form a protein.

      5. Endoplasmic Reticulum (ER): Some proteins, known as secretory or membrane proteins, may require further processing and modifications. They are directed to the endoplasmic reticulum (ER), where these modifications take place.

      6. Golgi Apparatus: After being processed in the ER, the proteins are then transported to the Golgi apparatus, where additional modifications occur. The Golgi apparatus acts as a sorting and packaging organelle, ensuring that the proteins are properly directed to their final destinations.

      7. Vesicle Transport: The Golgi apparatus packages the proteins into vesicles, small membrane-bound sacs. These vesicles transport the proteins to their final cellular locations, which may include secretion outside the cell or placement in various cellular compartments.

      It's essential to note that DNA does not pair directly with ribosomes. Instead, the genetic information in DNA is transcribed into mRNA, and it is the mRNA that interacts with ribosomes during translation. The Golgi apparatus does not package the mRNA but rather processes and packages the proteins synthesized from the mRNA.

      The central dogma of molecular biology describes the flow of genetic information from DNA to RNA to protein, which is fundamental to the functioning of living cells.
      (7 votes)
  • leafers ultimate style avatar for user Harrison
    I know that there are muscle cells, fat cells, blood cells and other types of cells in the body. Does every single cell have this same anatomy? Are there components that are present in every type of cell? If Sal's example cell is the prototypical cell that we memorize as students, can we identify what type of cell it is just based on the anatomy, or do we have to look at what DNA is present in the cell?
    (0 votes)
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    • male robot donald style avatar for user Tybalt
      Not every cell has the same anatomy. Two examples of this are red blood cells and muscle cells. Red blood cells eject all of their organelles when they mature so that they be more flexible when travelling through narrow spaces like capillaries. Meanwhile, muscle cells are so unusual that specialized terminology was created just to name the parts of it.

      For the purposes of identification, looking at the cell's form would usually be enough to identify the cell. Because form follows function, a cell would be shaped as such to carry out a certain job. For instance, take a heart muscle cell and compare it to a neuron. Heart muscle cells, on one hand, have much more mitochondria that the average cell, and has units that allow them to contract. The heart muscle cell needs these to beat without becoming fatigued. On the other hand, a neuron is unable to contract and does not have many mitochondria, but is long and branched to allow for communication.

      Does this help?
      (13 votes)
  • starky ultimate style avatar for user juju
    Free ribosome, he locked in the tha cell ✊😔⛓️
    (6 votes)
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  • starky seed style avatar for user Hisoka
    What is the difference in prokaryotic cells and eukaryotic cells?
    (4 votes)
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    • female robot amelia style avatar for user him
      Cellular Organization:

      Prokaryotic cells: Prokaryotic cells are relatively simple and lack a true nucleus. Their genetic material, a single circular DNA molecule, floats freely in the cell's cytoplasm without being enclosed in a membrane-bound nucleus.
      Eukaryotic cells: Eukaryotic cells are more complex and have a true nucleus that encloses the cell's genetic material. The DNA is organized into linear chromosomes and is separated from the cytoplasm by a nuclear membrane.
      Nucleus:

      Prokaryotic cells: No true nucleus; the DNA is found in the nucleoid region.
      Eukaryotic cells: Have a true nucleus, where the DNA is enclosed in a double-membrane nuclear envelope.
      Organelles:

      Prokaryotic cells: Lack membrane-bound organelles. They have ribosomes, but these are not enclosed in a membrane.
      Eukaryotic cells: Contain various membrane-bound organelles, including mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and more.
      Size:

      Prokaryotic cells: Generally smaller, with typical sizes ranging from 0.1 to 5 micrometers.
      Eukaryotic cells: Generally larger, with typical sizes ranging from 10 to 100 micrometers.
      Cell Division:

      Prokaryotic cells: Reproduce through binary fission, where the cell splits into two identical daughter cells.
      Eukaryotic cells: Undergo mitosis (for somatic cells) or meiosis (for sex cells) during cell division.
      Membrane-Bound Structures:

      Prokaryotic cells: Have a cell membrane and a rigid cell wall outside the membrane. Some may also have a capsule for protection and pili for attachment.
      Eukaryotic cells: Have a cell membrane, but the cell wall is present only in plant cells and some other organisms (e.g., fungi). Animal cells lack a cell wall but have a flexible cytoskeleton that provides structural support.
      Reproduction:

      Prokaryotic cells: Reproduce asexually by binary fission and can exchange genetic material through processes like conjugation, transformation, and transduction.
      Eukaryotic cells: Reproduce asexually or sexually, depending on the organism, and sexual reproduction involves the fusion of gametes (sex cells) from two parents.
      Prokaryotic cells are typically found in bacteria and archaea, while eukaryotic cells make up plants, animals, fungi, and protists. The distinction between these cell types is fundamental to understanding the diversity of life on Earth and the different mechanisms that govern cellular processes in living organisms.

      u r not hisoka u r not him bro
      (4 votes)

Video transcript

- [Instructor] What we're going to do in this video is give ourselves a little bit of a tour of eukaryotic cells. 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 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 your cellular membrane here. I drew it big, so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do some 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 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 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 the genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle, or the membrane 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. So that is the first membrane-bound organelle that we're gonna 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, but 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. Imagine extending from these pores, going into a space that has 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 nucleus. And this right over here, and this is just a rough diagram. That is our endoplasmic, endoplasmic... Not blasmic, 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 genetic information from DNA, and as we talk about in other videos it gets transcribed into mRNA. So that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. 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, 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 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 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 are making them rough. It looks that way in a microscope. So I'll just 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 can imagine, smooth endoplasmic reticulum. There are things known as golgi bodies. Once again, another fascinating name. You 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've just been produced, and packaging them so that they can be used outside of the cell, for example. 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 as the powerhouse of the cell, and that is the mitochondria. So I'll draw this mitochondria in magenta, because that's a nice powerful color. 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. So that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say let's see what we could see inside of this. This is where you 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've been independent organisms, independent cells. And at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells. And over time, they became so codependent that they started to replicate together. And mitochondria, in fact, became part of these eukaryotic cells. Now if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them because we don't have photosynthesis, but this is a chloroplast. And if you could see inside, you could see the little thylakoid stacks right over here. You could see the 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 membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast, or for sure the nucleus, and that might be something like a vacuole. And in plants, vacuoles tend to be very big. I could draw it, this is three-dimensional so I'll draw it on top of something that I've drawn before. So if a vacuole right over here, this is a... And in a plant it could be a fairly significant compartment inside. And in fact, it can even give structure to the plant itself because it is so big. And it contains water and enzymes. It's viewed as kind of a storage compartment. But it can also contain enzymes that help digest things, that help break things down so that they can be used in some way. So that is a vacuole. And they don't just exist in plants. They can also exist in animal cells. But in plant cells, 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 lysosome. So a lysosome right over here, that also is a compartment. And it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells. So it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there. 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 the cell. The big thing to appreciate is that cells are incredibly complex. There's all sorts of structures in here that help transport things and move things around. If you could shrink yourself down and look inside of a cell, it would look more complex than the most complex cities. There's all sorts of activities, things being moved around, shuttled around. The cell itself is replicating and copying things. And so this is just the beginning. We're just starting to scratch the surface of the complexity of the most basic unit of life.