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Current time:0:00Total duration:11:11

Video transcript

this is an animal and this is also an animal an animal animal animal carcass animal animal animal carcass again animal the thing that all of these other things have in common is that they're made out of the same basic building block the animal cell animals are made up of your run-of-the-mill eukaryotic cells and these are called eukaryotic because they have a true kernel in the Greek a good nucleus that contains the DNA and calls the shots for the rest of the cell also containing a bunch of organelles a bunch of different kinds of organelles and they all have very specific functions and all this is surrounded by the cell membrane of course plants are eukaryotic cells too but they're set up a little bit differently of course they have organelles that allow them to make their own food which is super nice we don't have those and also their cell membrane is actually cell wall it's made of cellulose it's rigid which is why plants can't dance if you want to know all about plant cells we did a whole video on it and you could click on it here if it's online yet it might not be a lot of the stuff in this video is going to apply to all eukaryotic cells which includes plants and fungi and protists now rigid cell walls that's cool and all but one of the reasons that animals have been so successful is that they're flexible membrane in addition to allowing them the ability to dance gives animals the flexibility to create a bunch of different cell types and organ types and tissue types that could never be possible in a plant so all that protect plants and give them structure prevent them from evolving complicated nerve structures and muscle cells that allow animals to be such a powerful force for you know eating plants animals can move around find shelter and food find things to mate with all that good stuff in fact the ability to move oneself around using specialized muscle tissue has been 100% trademarked by kingdom Animalia ah what about protozoans excellent point what about protozoans they don't have specialized muscle tissue they move around with cilia and flagella and that kind of thing so way back in 1665 British scientist Robert Hooke discovered cells with his kind of crude beta-version microscope he called themselves because they looked like bare Spartan monks bedrooms with not much going on inside Hooke was a smart guy and everything but he could not have been more wrong about what was going on inside of a cell there is a whole lot going on inside of a eukaryotic cell it's more like a city than a monk's cell in fact let's go with that a cell is like a city it has divine geographical limits of ruling government power plants roads waste treatment plants a police force industry all the things of bloomin metropolis needs to run smoothly but this city does not have one of those hippie governments where everybody votes stuff and talks things out at town hall meetings and crap like that nope think fascist Italy circa 1938 think Kim Jong Il's no I mean Kim Jong Un's North Korea and you might be getting a closer idea of how eukaryotic cells do their business let's start out with city limits so as you approach the city of you carry a palace there's a chance that you will notice something that a traditional city never has which is either cilia or flagella some eukaryotic cells have either one or the other of the structures cilia being a bunch of tiny little arms that wiggle around flagella being one long whip-like tail some cells have neither sperm cells for instance have flagella and our lungs and throat cells have cilia that push mucus up and out of our lungs cilia and flagella are made out of long protein fibers called microtubules and they both have the same basic structure 9 pairs of microtubules forming a ring around 2 central microtubules this is often called the 9 plus 2 structure anyway that's just so you know when you're approaching the city watch out for the cilia and flagella if you make it past the cilia you will encounter what is called a cell membrane which is a kind of squishy not rigid plant cell wall which totally encloses the city and all of its contents it's also in charge of monitoring what comes in and out of the cell kind of like the fascist border police the cell membrane has selective permeability meaning that it can choose what molecules come in and out of the cells for the most part and I did an entire video on this which you can check out right here now the landscape of you carry Oppel is important to note is a kind of wet and squishy bit of a swampland each eukaryotic cell is filled with a solution of water and nutrients called cytoplasm and inside of this cytoplasm is a scaffolding called the cytoskeleton it's basically just a bunch of protein strands that reinforce the cell centrosomes are special part of this reinforcement they assemble long microtubules out of proteins that act like steel girders that hold all the city's buildings together the cytoplasm provides the infrastructure necessary for all the organelles to do all of their awesome amazing business with the notable exception of the nucleus which has its own kind of cytoplasm called the nucleoplasm which is a more luxurious premium environment befitting the cells beloved leader but we'll get to that in a minute first let's talk about the cells highway system the endoplasmic reticulum or just ER or organelles that create a network of membranes that carry stuff around the cell these membranes are phospholipid bilayer our same as in the cell membrane there are two types of ER there's the rough and the smooth fairly similar but slightly different shapes led to different functions the rough ER looks all bumpy because it has ribosomes attached to it and the smooth ER doesn't so it's a smooth network of tubes smooth ER acts is a kind of factory warehouse in the cell city it contains enzymes that help with the creation of important lipids which you'll recall from our talk about biological molecules and you have phospholipids and steroids that turn out to be sex hormones other enzymes in the smoothie are specialized in detoxifying substance like noxious stuff derived from drugs and alcohol which they do by adding a carboxyl group to them making them soluble in water finally the smooth ER also stores ions and solutions that the cell may need later on especially sodium ions which are used for energy and muscle cells so the smooth ER helps make lipids while the rough ER helps in the synthesis and packaging of proteins and those proteins are created by another type of organelle the ribosome ribosomes can float freely throughout the cytoplasm or be attached to the nuclear envelope which is where they're spat out from and their job is to assemble amino acids into polypeptides as the ribosome builds an amino acid chain the chain is pushed into the ER when the protein chain is complete the ER pinches it off and sends it to the Golgi apparatus and the city that is the cell the Golgi is the post office processing proteins are packaging them up before sending them wherever they need to go calling it an apparatus makes it sound like a bit of complicated machinery which it kind of is because it's made up of like these stacks of membranous layers that are sometimes called Golgi bodies the Golgi bodies can cut up large proteins into smaller hormones and can combine proteins with carbohydrates to make various molecules like for instance snot the body's packaged these little goodies into sacks called vesicles which have phospholipid walls just like the main cell membrane then ship them out either to other parts of the cell or outside the cell wall we learn more about how vesicles do this in the next episode of crash course the Golgi bodies also put the finishing touches on the lysosomes lysosomes are basically the waste treatment plants and recycling centers of the city these organelles are basically sacks full of enzymes that break down cellular waste and debris from outside of the cell and turn it into simple compounds which are transferred into the cytoplasm as new CEL building materials now finally let us talk about the nucleus the beloved leader the nucleus is if highly specialized we're now that lives in its own double membranes high-security compound with its buddy the nucleolus and within the cell the nucleus is in charge in a major way because it stores the cell's DNA it has all the information the cell needs to do its job so the nucleus makes all the laws for the city or does all the other organelles around telling them how and when to grow what to metabolize what proteins to synthesize how and when to divide the nucleus does all this by using the information blue printed in its DNA to build proteins that will facilitate a specific job getting done for instance on January 1st 2012 let's say a liver cell needs to help break down an entire bottle of champagne the nucleus in that liver cell would start telling the cell to make alcohol dehydrogenase which is the enzyme that makes alcohol not alcohol anymore this protein synthesis business is complicated lucky for you we will have or may already have an entire video about how it happens the nucleus holds its precious DNA along with some proteins in a web-like substance called chromatin when it comes time for the cell to split the chromatin gathers into rod-shaped chromosomes each of which holds DNA molecules different species of animals have different numbers of chromosomes we humans have 46 fruit flies vey hedgehogs which are adorable but you know less complex than humans have 90 now the nucleolus which lives inside of the nucleus is the only organelle not enveloped by its own membrane it's just a gooey splotch of stuff within the nucleus its main job is creating ribosomal RNA or rRNA which it then combines with some proteins to form the basic units of ribosomes once these units are done the nucleolus spits them out of the nuclear envelope where they are fully assembled into ribosomes lytic leus then sends orders in the form of messenger RNA or mRNA to those ribosomes which are the henchmen that carry out the orders in the rest of the cell how exactly the ribosomes do this is immensely complex and awesome so awesome in fact that we're going to give it the full crash course treatment and entire episode and now for what is totally objectively speaking of course the coolest of the animal cell its power plants the mitochondria the smooth oblong organelles where the amazing and super important process of respiration takes place this is where energy is derived from carbohydrates fats and other fuels and is converted into adenosine triphosphate or ATP which is like the main currency that drives life and you carry a police you can learn more about ATP and respiration in an episode that we did on that now of course some cells like muscle cells or neuron cells need a lot more power than the average cell in the body and so those cells have a lot more mitochondria per cell but maybe the coolest thing about mitochondria is that long ago animal cells didn't have them but they existed as their own sort of bacterial cell and it one day one of these things ended up inside of an animal cell probably because the animal cell was trying to eat it but instead of eating it realized that this thing was really super smart and good at turning food into energy and it just kept it it stayed around and in this day they sort of act like their own separate organisms like they do their own thing within the cell they they replicate themselves they even contain a small amount of DNA now what may be even more awesome if that's possible is that mitochondria are in the egg cell when an egg gets fertilized and those mitochondria have DNA but because mitochondria replicate themselves in a separate fashion it doesn't get mixed with the DNA of the father it's just the mother's mitochondrial DNA that means that your and my mitochondrial DNA is exactly the same as the mitochondrial DNA of our mothers and because this special DNA is isolated in this way scientists can actually track back and back and back and back to a single mitochondrial Eve who lived about 200,000 years ago in Africa all of that complication in mystery and beauty and one of the cells of your body complicated yes but worth understanding
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