If you had to think back about the most exciting day you ever had in the science classroom, which day would that be? Looking back through the years, we have a few. The time we participated in an earthworm dissection, the time we took apart an owl pellet, the osmosis eggs, all of the fruit flies and genetic experiments. Oh, I could go on.
But I will never forget one day in my ninth grade science class. My teacher brought in pond water. And I put one drop of pond water on a microscope slide and saw the most amazing thing ever.
I saw an amoeba. A single-celled amoeba on that microscope slide. And I was forever stuck on science from that point on.
Because I could not believe that this little cell was there, alive on this slide, still eating because that's what amoebas do a lot. But to imagine that every person is actually made of billions of cells, of course not amoeba cells, but animal cells, billions of animal cells, that's fascinating. In fact, it really makes you reflect on some of the incredible statements of the modern cell theory. The modern cell theory includes the following. First, that the cell is the smallest living unit in all organisms.
And second, that all living things are made of cells, one or more cells. The amoeba I observed was a single-celled organism, so unicellular. Humans are made of many cells, so multicellular.
And third, all cells come from other pre-existing cells. You know, cells have their own little world inside them. They carry genetic information, they can divide, many have functions and processes that their organelles, structures inside them, can take care of.
On our planet, we can divide cells into two major groups. As a cell, you're either a prokaryote or a eukaryote. Bacteria and RK are prokaryotes, but everything else plants, animals, fungi, protists are eukaryotes.
Both prokaryotes and eukaryotes have genetic material. Both have cytoplasm. Both have ribosomes, which are small organelles that make protein. Both have cell membranes, which are small organelles that make protein. control what goes in and out of the cell.
But what makes them different is a big deal. Prokaryote, the pro rhymes with no, and they have no nucleus, which holds the genetic material and controls a cell's activities. Prokaryotes have no membrane-bound organelles. Membrane-bound organelles are fancy organelles like the nucleus and mitochondria and Golgi apparatus.
Eukaryotes, the U rhymes with do, they do have membrane-bound organelles. So now you may be wondering, what do the organelles do? What are their functions? Well, you know our style.
We love our science with a side of comics. So we want to take you on a tour of the ride of your life…into the inside of a cell. Now, to start our trip, we're going to have to get through this cell membrane, also called a plasma membrane.
It's selectively permeable, which means it'll only let certain select materials in and out, but by doing so, it will allow the cell membrane to be it keeps things in the cell stable, also known as keeping homeostasis. And we have an entire video on just the membrane itself, which is found in all cells. But for now, we're just going to have to squeeze through this protein in the membrane. Now inside the cell, we find ourselves in this jelly-like material called cytoplasm. It surrounds all these internal cell structures, and you'll find it inside both prokaryotes and eukaryotes.
Now organelles that are floating around in the cytoplasm can have more support than you might think. Cells contain a cytoskeleton, which is a collection of fibers that can provide support for the cell and its organelles. The cytoskeleton can even play a major role in cell movement. The cytoskeleton actually deserves its own video because it's very complex and its organization can vary depending on what kind of cell you're looking at.
Moving through this cytoplasm, let's start with ribosomes. They are not membrane-bound organelles and they're going to be in both prokaryotes and eukaryotes. They make protein, which is really important because that's what so much of genetic material codes for protein. Ribosomes can be free in the cytoplasm, but they can be attached to another organelle too, which we'll talk about a little bit later.
We're now going to focus on organelles that will be membrane-bound, so we're going to be focusing on organelles that you would find in a eukaryote cell. This takes our travel to the big boss, the nucleus. Now in eukaryotes, it holds the genetic material. Genetic material as in DNA, for example. Both prokaryotes and eukaryotes have DNA, but if you're a eukaryote, you have a nucleus to put it in.
The nucleus controls the cell's activities, and inside it, it has a nucleolus, which is where ribosomes can be produced. Attached to the membrane of the nucleus, or nuclear membrane, you will find the endoplasmic reticulum, ER for short. It does a lot of processing of molecules for the cell, like protein folding, and it's highly involved in actually transporting those molecules around.
Like a highway. There's a rough ER, which has ribosomes attached to it, making it, as you can imagine, rough. And then smooth ER, which doesn't have the ribosomes. Rough ER specifically tends to be involved with protein producing and transporting, because remember that ribosomes make protein.
Molecules that leave the ER can be sent away in vesicles that actually pinch off the ER themselves. Now smooth ER has many additional roles including detoxification which is one reason why your liver cells tend to have a lot of smooth ER. And another additional role of smooth ER is that it can make some types of lipids.
Next the Golgi apparatus. It's the ultimate packaging center. It can receive items from the transport vesicles that pinched off the ER. It has enzymes that can modify molecules it may receive, and sorts the material it receives as well. It can determine where to send those molecules, including some that may eventually be sent to the membrane, so they can be secreted, which means items that can be sent out of the cell.
So with all that's going on in here, you might start to wonder, what's powering this thing? The mighty mitochondria, or mitochondrion if you're just talking about one. They're like power plants.
The mitochondria make ATP energy in a process called cellular respiration. Now, it's not the type of power plant that you might think of. It runs on glucose, which is a sugar, and it needs the presence of oxygen to efficiently make ATP energy.
Now, at this point, we need to mention that eukaryotes are not a one-size-fits-all. Animal cells can have differences from plant cells. We have a fork.
in the road here. For example, plant cells not only have mitochondria, but they can also have these awesome organelles called chloroplasts. Chloroplasts actually make glucose by using light energy in a process known as photosynthesis.
They tend to even have a green look to them because they have a pigment that captures the light energy and it reflects green light. Now both plant and animal cells can have vacuoles. Now vacuoles can have a lot of different functions, but Many types act as storage of materials.
Plant cells can have one large vacuole called a central vacuole, while animal cells can have smaller, several vacuoles. Now, remember how we already said that all cells have membranes? They do. But plant cells additionally can have a cell wall, which is a layer that offers additional protection and shape maintenance that animal cells do not.
Hmm, now how do we get out of this animal cell that we've been in? Well, we could get out like a protein would. So if we were a protein, we would only be made because of instructions from DNA. And remember that in eukaryotes, DNA is found in the nucleus.
We would be made by a ribosome because ribosomes make protein. The ribosomes could be attached to the rough ER. And the rough ER highway would provide a vesicle to send us to the Golgi apparatus where sorting can take place. And if we're tagged for being secreted, We could be sent off through a vesicle from the Golgi to the membrane. Out we go!
Just keep in mind that in our quick tour, there are still so many more awesome organelles found in lots of different types of eukaryote cells to continue exploring, so to the Google for more. That's it for the Amoeba Sisters and we remind you to stay curious.