good afternoon class uh today we're going to cover unit 4 chapter 3 part c this is the last uh chapter before your test so now we're going to look at cells um and their uh components part two the cytoplasm so all cellular material that is located between the plasma membrane and the nucleus is the cytoplasm so what's inside the cytoplasm there's the cytosol which is the gel-like solution which is aqueous and has soluble molecules such as proteins salts sugars there are include inclusions these are insoluble molecules vary with cell type for example some cell types would have glycogen granules some would have pigments or lipid drop droplets or vacuoles or crystals and the organelles so this is going to be our primary focus today the organelles that make up these cell so it's basically the metabolic machinery structures of cell each with specialized function either membranous or non-membranous in other words some of them will be enclosed by a membrane and others will not section 3.7 cytoplasmic organelles so uh of the ones that are membranous we have the mitochondria the endoplasmic reticulum the golgi apparatus peroxisomes and lysosomes of those that are non-membranous are the ribosomes the cytoskeleton and the centrioles so what's the purpose of a membrane it allows for compartmentalization which is crucial to cell functioning let's start with the mitochondria mitochondrion is singular mitochondria is plural it's the powerhouse of the cell because it produces most of the cells energy molecules in the form of atp and it does it using oxygen so it's an aerobic process called aerobic cellular respiration so mitochondria are enclosed by double membranes there's an inner membrane that has many folds and these folds are called cristae and the cristae are embedded with membrane proteins that play a role in cellular respiration mitochondria contain their own dna rna and ribosomes so they're independent of the nucleus of a cell they resemble bacteria and are capable of the same type of cell division bacteria use which is called fission so this is what a mitochondrion looks like so notice there are two membranes an outer membrane and an inner membrane and the inner membrane the little folds are called cristae the inside that compartment within the inner membrane is called the matrix 314 mitochondrion so there's the cell and inside you have those bean-shaped structures called the mitochondria so if we look at one mitochondrion you can see the outer mitochondrial membrane and the inner membrane and the little folds are called cristae and within the that inner compartment is called the matrix now notice within the matrix there's mitochondrial dna so basically the mitochondrion has its own dna and it's got its own ribosomes this figure shows you how a mitochondrion divides and separates okay this is very similar to the way bacteria uh divide uh as you will see next year in your microbiology class so first it starts off as small and it grows and then it's going to undergo fission so it's going to separate in two and become two mitochondria the next organelle are known as the ribosomes okay so these are non-membranous and their job is protein synthesis in other words making proteins for the cell what is a ribosome made up of it's made up of protein and ribosomal rna which is different from other rnas so this rrna is specific to ribosomes it's called ribosomal rna so there's two switchable forms of ribosomes in the cell there are free ribosomes and membrane-bound ribosomes the free ribosomes these are free-floating uh so it's the site of synthesis of soluble proteins that function in the cytosol or other organelles whereas the membrane-bound ribosomes are attached to the membrane of the endoplasmic reticulum so it's the site of synthesis of proteins that will be incorporated into membranes or lysosomes or for uh for exocytosis from the cell a ribosome is made up of two subunits a large subunit and a small subunit as we can see in this figure in this figure we can see the ribosomes that are attached to the rough endoplasmic reticulum so those little blue dots are ribosomes and that's where protein synthesis is is occurring and that happens in the rough er as opposed to the smooth er that has another function this figure shows the two types of ribosomes the free ribosomes that are floating free and the ribosomes that are associated with the rough endoplasmic reticulum next we're going to talk about the endoplasmic reticulum so it consists of a series of parallel interconnected cisterns which are flattened membranous tubes that enclose a fluid filled interior the endoplasmic reticulum is continuous with the outer nuclear membrane there are two types the rough er and the smooth er this figure shows the two types of endoplasmic reticulum rough endoplasmic reticulum is called rough because it's studded with ribosomes and the smooth looks like a system of interconnecting pipes and notice the rough endoplasmic reticulum is continuous with the outer nuclear envelope figure 315 the endoplasmic reticulum so here if you look at its uh position within with respect to the cell okay so the purple part there that's the nucleus okay so notice how it's continuous with the the nucleus and the rough endoplasmic reticulum are continuous uh figure a the uh you can see the um cisterns of the uh rough endoplasmic reticulum you can see the ribosomes on the outside whereas if you look at the smooth endoplasmic reticulum it's smooth in appearance figure b is an electron micrograph of both the smooth and rough endoplasmic reticulum it's been magnified 25 000 times so the rough endoplasmic reticulum is it's the external surface the external surface appears rough because we said it is studded with these attached ribosomes it's the main site of protein synthesis that will be secreted from the cell so it's the site of synthesis also of many plasma membrane proteins and phospholipids proteins will enter the cisterns as they are synthesized and are modified as they wind through the fluid filled tubes the final protein is enclosed in a vesicle and it's sent to the golger golgi apparatus for further processing the other hand the smooth endoplasmic reticulum is a network of looped tubules that are continuous with the rough er the end the enzymes found in its plasma membrane remember their inter their integral proteins they function in the in lipid metabolism so um a breakdown of lipids cholesterol and steroid-based hormone synthesis the making of lipids for lipoproteins also for absorption synthesis and transport of fats detoxification of certain chemicals like drugs pesticides so something like the liver the liver would contain a lot of smooth endoplasmic reticulum because its job is to detoxify uh drugs and pesticides or for example the uh you know the testes they produce uh testosterone so they would have lots the testes would have lots of smooth endoplasmic reticulum also the smooth er is will convert glycogen to free glucose so again another function of the liver and also the smooth endoplasmic reticulum will store and release calcium so the sarcoplasmic reticulum is a specialized smooth er which is found in skeletal and cardiac muscle cells golgi apparatus is an organelle that looks it's stacked it's made up of stacked and flattened membranous cistern sacs its job is to modify concentrate and package proteins and the lipids that it received from the rough er there are three steps that are involved the transport vesicles from the endoplasmic reticulum will fuse with the cis interface of the golgi the proteins or lipids taken inside are further modified tagged sorted and packaged and the golgi then is like the traffic director controlling which of the three pathways final products will make as new transport vesicles pinch off from the trans or outer face of the golgi apparatus the figure on the left shows you the golgi apparatus on its own so the cis phase is what received it receives the incoming transport vesicles and then there's packaging that occurs within the lumen of the cisternae and then the trans face is going to make sure will will form the secretory vesicles that will send whatever was inside uh then that was sorted to different destinations on the right you can see the golgi apparatus which is very strategically located next to the rough endoplasmic reticulum and there you see it you know with the transport vesicles so they can either be used for exocytosis or it can also can also process uh molecules are coming into the cell via endocytosis the 316 again the golgi apparatus this one is from your book figure a many vesicles in the process of pinching off from the golgi apparatus so notice there's the cis face receiving side of the golgi apparatus then there's a little cisterns and then there's formation of new vesicles at the level of the trans face that's the shipping side of the golgi apparatus so depending on its contents the final transport vehicle can take one of three pathways pathway a the secretory vesicles containing proteins to be used outside of the cell will fuse with the plasma membrane and exocytosis contents pathway b the vesicles containing lipids or transmembrane proteins will fuse with the plasma membrane our organelle membrane inserting contents directly into destination membrane in pathway c the lysosomes containing digestive enzymes remain in the cell holding the contents in a vesicle until needed figure 317 processing and distribution of newly synthesized proteins so in part one the vesicles move from the er to the golgi the vesicles containing proteins but off of the rough er they migrate and fuse with membranes of the golgi apparatus then the proteins are modified inside the golgi apparatus some sugar groups are trimmed while others are added in some cases phosphate groups are added proteins are distributed so proteins are tagged or addressed sorted and packaged in three different types of vesicles which butt off the concave trans face the shipping side of the golgi stack these vesicles have three possible fates depending on the proteins they carry so in 3a the proteins these ones are for secretion so proteins destined for export are packaged into secretory vesicles that migrate to the plasma membrane and dump their contents by exocytosis in 3b these are proteins destined for membranes so vesicles containing lipids and transmembrane proteins destined for the plasma membrane or other cellular membranes fuse with and are incorporated into those membranes and pathway c that these uh contain digestive enzymes uh so inactive digestive enzymes are packaged into vesicles that eventually become lysosomes or fuse with lysosomes roxysomes are membranous sacs that contain powerful detoxifying substances that neutralize toxins so free radicals are toxic they're highly reactive molecules that are natural byproducts of cellular metabolism these are always being produced and they can cause havoc to the cell if they're not detoxified there are two main detoxifiers oxidase and catalase oxidase uses oxygen to convert toxins to hydrogen peroxide which is itself toxic however peroxisome also contains catalase which converts hydrogen peroxide to water which is harmless peroxisomes also play a role in the breakdown and the synthesis of fatty acids now let's look at lysosomes these are spherical membranous bags containing digestive enzymes they're considered safe sites because they isolate potentially harmful intracellular digestion from the rest of the cell their job is to digest ingested bacteria viruses and toxins so something like a white blood cell would have lots of lysosomes they also break down non-functional organelles um also they have metabolic functions they break down and release glycogen break down and release calcium from the from the bone and intracellular release in injured cells causes cells to digest themselves called autolysis here's a figure of a cell and the arrow is pointing to the lysosome clinical homeostatic imbalance 3.3 so lysosomal storage diseases result when one or more lysosomal digestive enzymes are mutated and do not function properly there's a disease called taysacs it's actually a condition in which the patient lacks a lysosomal enzyme that is needed to break down glycolipids in brain cells so the glycolipids as a result will build up and interfere with the proper functioning of the nervous system it's seen predominantly in infants of central european jewish descent and causes seizures mental retardation blindness and death before age five the endomembrane system consists of membranous organelles discussed so far so the er both the rough and smooth the golgi apparatus all the secretory vesicles and lysosomes are part of the endomembrane system as well as the nuclear and plasma membranes these membranes and organelles work together to produce degrade store and export biological molecules and also to break down potentially harmful substances your 319 shows the components of the endomembrane system so we start with the nuclear envelope which surrounds the nucleus which is connected with the smooth endoplasmic retic reticulum uh so there's all these secretory vesicles that are moving around uh then there's the contents let's say from the smooth and the rough endoplasmic reticulum will pass through the golgi apparatus and then there's transport vesicles and we've already talked about that and also lysosomes are involved with um in this endomembrane system because they're part of intracellular digestion the cytoskeleton cyto means cell skeletons of the skeleton of the cell is an elaborate network of rods that run throughout the cytosol hundreds of different kinds of proteins link the rods to other cell structures so it's also it acts as the cells bones ligaments and muscle by playing a role in movement of the cell components there are three types microfilaments intermediate filaments and microtubules this figure shows the three components of the cytoskeleton we can see the intermediate filaments the microtubules and the microfilaments which are made up of the protein actin so let's start looking at microfilaments these are the thinnest of all the cytoskeletal elements we said that they're made up of the semi-flexible strands of protein actin each cell has a unique arrangement of strands although share a common terminal web which is a dense cross-linked network of microfilaments that are attached to the cytoplasmic side of the plasma membrane and it strengthens the cell surface and helps to resist compression some are also involved in cell motility so the movement of the cell for example in uh if you think about macrophages so types of white blood cells that do that have pseudopods and move around also changes in a cell shape or in the process of endocytosis and exocytosis figure 320a cytoskeletal elements support the cell and help to generate movement so in a we see microfilaments which are made up of strands of spherical protein subunits called actin okay so the whole thing there is called the microfilament and the little beads are the actin the intermediate filaments are as the name suggests the size is in between microfilaments and microtubules they're tough insoluble rope-like protein fibers they're composed of a tetramer fibrils of tetramer fibrils twisted together resulting in one strong fiber they help the cell resist pulling forces so filaments will attach to desmosome plaques and act as an internal guy wires some have special names they're called neurofilaments in nerve cells this is something we'll see next semester and keratin filaments in epithelial cells which we saw in the lab this week figure 320b cytoskeletal elements support the cell and help to generate movement so here we look we see the intermediate filaments they're tough insoluble protein fibers constructed like woven ropes composed of tetramer fibrils and [Music] yes okay microtubules are the largest of the cytoskeletal elements they consist of hollow tubes composed of the proteins subunits called tubulins which are constantly being assembled and disassembled most will radiate from a centrosome area of the cell so their job is to determine the overall shape of the cell and distribution of organelles so many organelles are tethered to microtubules to keep organelles in place so they don't just float around in the cytosol and many substances are moved through cell throughout the cell by motor proteins which use microtubules as tracks this figure shows the centrosome which is made up of two centrioles which are made up of microtubules 320c cytoskeletal elements support the cell and help to generate movement so here we see microtubules which are made up of their hollow tubes of spherical protein subunits called tubulin so we mentioned motor proteins these complexes that function in movement they can help in movement of organelles and other substances around the cell and they use the microtubules as tracks to move their cargo and they're of course powered by uh atp uh there's some actually very interesting videos uh out there showing how they move uh you have the the motor proteins would be something like dynein and kinesin and they're moving for example cargo picture like you know those vehicles those transport vehicles they don't just bump around and float around in the cell they're actually moving along the tracks and they're being moved by these motor proteins nitrosomes and centrioles okay so i showed you a picture before the centrosome is located near the nucleus it means cell center it is a microtubule microtubule organizing center consisting of a granular matrix and a pair of centrioles that are bar barrel shaped microtubular organelles that lie at right angles to each other so newly assembled microtubules radiate from the centrosome to the rest of the cell some microtubules aid in cell division and some will form cytoskeletal tract system centrals also form the basis of cilia and flagella which are locomotory organelles let me just uh fix that it's acilian flagella are not organelles they are structures they're locomotory structures figure 321a we see a centrosome which is made up of a pair of centrioles and these are important for organizing the microtubules figure b in figure 321 b we can see this is an electron micrograph of uh of a cross-section of a centriole you can see that there are nine sets of three microtubules so we call this a 9-3 arrangement of microtubules in 3.8 cellular extensions so certain cells have structures extending from the cell surface examples would be cilia and flagella which help in the movement of the cell or of materials across the surface of the cell and microvilli these are finger-like projections that extend from the surface of the cell to increase the surface area usually for for let's say for digestion or absorption or secretion figure on the left shows cilia in the walls of the bronc bronchi and on the right the figure shows the flagellated sperm this figure shows a section of the small intestine so you can see the villa villi and if you look at the small section of the villi if you magnify it you can see that there are microvilli for increased digestion and absorption of nutrients let's look at cilia and flagella a little more closely so cilia are whip-like motile extensions on surfaces of certain cells such as the respiratory cells of the trachea for example so thousands of cilia work together in a sweeping motion to move substances like mucus across the cell surface in one direction and for respiratory cells it would be towards the direction of the mouth because we don't want mucus and debris to accumulate in the lungs flagella on the other hand are longer extensions that propel the whole cell so an example would be the tail of the sperm so both structures are made up of microtubules that are synthesized by centrioles that are called basal bodies because they form the base of each cilium and flagellum this figure shows the structure the ultrastructure of the cilia and flagella so if you notice on the left the basal body also known as the kinetosome is what gives rise to either cilia or flagella they're both basically cilia are shorter and flagella are longer and there's usually more cilia than flagella in you know like in a cell uh so if you follow it to its apical surface okay through the outside to the outside you will notice that both cilia and flagella have a 9 2 arrangement of microtubules so cilia and flagella have a nine two arrangement of microtubules so there's basically nine sets of double tubes surrounding a central pair of doublets which is slightly different from the nine zero pattern of centrioles uh it's interesting because in some books they call it a nine plus zero pattern because zero because there are no tubules in the center but in other books it's often referred to as a ninth rearrangement okay but it's just the detail so celia movements alternate between a power stroke and a recovery stroke this alteration produce produces a current at the cell surface that moves the substances forward this is figure 322 the structure of a cilium cilium is the singular for cilia so again note the nine plus two arrangement of microtubules there are nine sets of two figure three point twenty three ciliary function so in figure a it just shows you the movement of the of cilia so there's a power or propulsive stroke and then a recovery stroke it's pretty much similar to when you row a boat so in figure b traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces so you can see the layer of mucus that's being moved in one direction microvilli okay so these are minute finger like extensions of the plasma membrane that project from the surface of cell select cells for example the intestinal cells that i've showed you i've shown you a picture before and also kidney tubule cells certain kidney tubule cells will have microvilli which we'll cover next semester and the purpose is to increase the surface area for absorption so they have a core of actin microfilaments that is used for the stiffening of projections 3.24 we can see a an epithelial cell that is made up of a microvilli so uh you can see at the figure on the right that at the base you would have actual actin filaments and the terminal web that we mentioned earlier part three of the this powerpoint is the nucleus it's the largest organelle and it contains the genetic library of blueprints for the synthesis of nearly all cellular proteins so it's basically contains the instructions to make those proteins it responds to signals that dictate the kinds and amounts of proteins that are needed to be that need to be synthesized most cells are uninucleate which means they only have one nucleus but skeletal muscle certain bone cells and some liver cells are multinucleate that means they have many nuclei and red blood cells are a nucleate means that they don't have a nucleus section 3.9 structure of the nucleus so these are the uh structures that are associated with the nucleus the nuclear envelope the nuclear nucleoli and chromatin they're 3.25 a the nucleus so you can see that kernel that round structure which is made up of a nuclear envelope studded with pores or nuclear pores and inside you have chromatin which we'll talk about and uh the innermost is called the nucleolus let's start with the nuclear envelope so it's a double membrane barrier that encloses the jelly-like fluid called the nucleoplasm okay so the nuclear envelope is in fact two membranes so the outer layer is continuous with the rough er and like the rough er is studded with ribosomes whereas the inner layer called the nuclear lamina is a network mesh of proteins that maintains the nuclear shape and acts as scaffolding for the dna we have nuclear pores that allow substances to pass into and out of the nucleus they're guarded by nuclear pore complex which regulates the transport of specific large molecules so not everything is allowed to enter the nucleus the nucleus is well protected and not everything is allowed to leave the nucleus so for example example something like dna would not be allowed to leave the nucleus this figure shows a really nice picture of the cell nucleus and its components so it's got the nuclear envelope which is made up which has nuclear pores and nucleoplasm which contains the chromatin and the nucleolus at the center so now we're at the nucleoli nucleolus is one nucleoli is plural so that's these dark staining round bodies within the nucleus that are involved in ribosomal rna synthesis and ribosome subunit assembly so the ribosomes are made at the level these subunits remember there's a large subunit and the smaller subunit is made at the level of the ribosomes and then they're assembled it's associated with the nuclear organizer regions that contain the dna that calls for ribosomal rna and usually one or two per cell the chromatin which is found within the nucleoplasm consists of 30 thread-like strands of dna 60 of histone proteins that are associated with that dna and 10 rna it's arranged in fundamental units called nucleosomes which consists of dna wrapped around those histone proteins chemical alterations of histones have an effect on dna and therefore can help regulate gene expression chromosomes are when we see chromosomes they're basically condensed chromatin so chromatin that has been wrapped really tightly the condensed state helps protect fragile chromatin threads during cell division this figure shows the structure of a chromosome okay so if we start you know chromosomes are made up of the double helix and it's wrapped around these beads of nucleosomes and to form so it's wrapped around twice in fact every dna strand is wrapped around twice and uh around and so the whole thing is called the nucleosome and then that forms chromatin the chromatin fiber and once it's really coiled and packed it's a chromosome 3.26 a chromatin and chromosome structure okay so here again if you start at one dna is the double helix and it's wrapped around those histones it's wrapped around twice in fact around eight of those uh so nucleus nucleosome is made up of it's about 10 nanometers in diameter it's made up of eight histone proteins wrapped by two wines of the double dna double helix figure 3.26 b so at this level of packing you see a tight helical fiber and then when the chromosome is at the midpoint of cell division called metaphase then it's made up of these two sister chromatids that are tightly packed together into this recognizable chromosome so basically uh on the left you can see the nucleus containing the chromatin so when the so chromatin appears diffused it looks like a plate of spaghetti okay when the cell is non-dividing when the cell is not in the cell does not have to divide that's what it looks like but as soon as the cell divides then the chromatin is going to condense into that condensed chromosome that we see on the right and now it's um uh it's ready for is an animation 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 [Music] 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 and that contains the dna and calls the shots for the rest of the cell also containing a bunch of organelles there's 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 their 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 cell 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 protozoa 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 hook 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 hook 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 cell in fact let's go with that a cell is like a city it has divine geographical limits a ruling government power plants roads waste treatment plants a police force industry all the things a booming metropolis needs to run smoothly but this city does not have one of those hippie governments where everybody votes on 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 eukaryopolis 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 these structures cilia being a bunch of tiny little arms that wiggle around in 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 flagellar are made out of long protein fibers called microtubules and they both have the same basic structure nine pairs of microtubules forming a ring around two central microtubules this is often called the nine plus two 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 in 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 eukaryopolis important to note is a kind of wet and squishy it's a bit of a swamp land 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 cell's 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 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 slightly 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 smoothie rx 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 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 and 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 bodies package 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 cell building materials now finally let us talk about the nucleus the beloved leader the nucleus is a highly specialized organelle that lives in its own double membrane high security compound with its body 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 and orders 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 blueprinted 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 vape 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 the nucleus 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 an entire episode and now for what is totally objectively speaking of course the coolest part of the animal cell it's power plants the mitochondria these 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 in eukaryopolis 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 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 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 and mystery and beauty in one of the cells of your body it's complicated yes but worth understanding review time another somewhat complicated episode of crash course biology if you want to go back and watch any of the stuff that we talked about it to reinforce it in your brand if you didn't quite get it just click on the links and it'll take you back in time to when i was talking about that mere minutes ago thank you for watching if you have questions for us please ask below in the comments or on twitter or on facebook and we will do our best to make things more clear for you we'll see you next time