Transcript for:
Cell Structure and Function Overview

i'm here to talk to you about cell structures and their functions this lecture is not about the plasma membrane or transport across the plasma membrane that is a separate lecture so we're talking about primarily the structures inside a cell today we're going to talk about prokaryotic cells briefly just not in a lot of detail but a little bit of detail we're mostly focusing on eukaryotic cells in this lecture first thing i want to note is that cells are not round so you might have at some point had a biology class where our cells were all drawn as circles on the board depending on what tissue type we're talking about cells are all different shapes so you you'll take anatomy hopefully eventually uh some of you and if you do take anatomy you will look at the different human tissue types and you will learn that cells have all types of different shapes depending on what that cell's job is where it's found in the body so the cell on the screen is not a round cell right it's it's not round at all the nucleus is round but it's also important to realize this is not a flat structure it's three-dimensional and it's not just this big gelatinous blob there's a lot going on in the middle here two major categories of cells that exist in living organisms prokaryotic cells and eukaryotic cells and at the very beginning of the semester we talked about what types of organisms are prokaryotes and what type are eukaryotes remember that term prokaryote really means before nucleus and eukaryote means true nucleus so that is the main difference between those two cell types but we will get into a little bit more detail today about the major differences between those two cell types you can see that included in the prokaryotes are bacteria in archaea whereas if you look at the eukaryotes the animals the plants and the fun the end of the term we will talk about protists and fungi in more detail we will talk about plants a little bit when we especially when we talk about photosynthesis so today we're mostly focusing on animal cells although we will point out some important structural differences between plant and animal cells a really important concept to understand is that cell size is limited so when organisms were first evolving they were all single-celled the first organisms on earth were single-celled single-celled organisms can only get a certain size they can't get huge and the reason for that is this concept of surface area to volume ratio if materials are having to move through the cell by simple diffusion okay which we'll learn about in more detail when we get to the transport across cell membrane lecture but the idea of diffusion is that materials move based on concentration gradient so this is going to be movement of molecules from an area of higher concentration to an area of lower concentration that's concentrating so to area of lower concentration so from high to low in the means without any energy required okay so if i if i have a cell and i have a lot of a molecule outside the cell and just a little bit of that molecule inside the cell these molecules will start moving into the cell by simple diffusion until equilibrium is reached that really means equal on both sides of the membrane so equal inside the cell and outside the cell so that movement of molecules with no energy required is called diffusion a lot of simple organisms move materials through their body and from the outside to the inside just based on simple diffusion so if you have a really big cell so let's look at this picture here this is a pretty fat cell if you look at the surface area because of the surface area imagine the whole outside of the cell in three dimensions all the way around and then this area is the volume okay so that's the volume on the inside the whole outside is the surface area if you're moving materials from the outside you need a big surface area but not a lot of volume the more volume you have the harder it's going to be to get those molecules from the outside all the way to the center so they're going to diffuse in but if you need them to get all the way to the center of the cell that's going to take a long time if that's a fat cell versus look at these tiny cells if you have molecules out here that need to move in by simple diffusion that's not going to take long so this is a very important concept as cells get bigger the volume increases faster than the surface area in other words that surface area to volume ratio decreases you have less surface area compared to the volume cells can only get so big because of that because cells are having to move materials around by diffusion it's not possible if that cell gets too big so the only way organisms were able to get larger is by becoming multicellular if you have a lot of little cells that's a better plan than having one big cell you also can then start specializing those individual cells to perform different categories of function and tissues can start to develop and organisms can become more complex so as organisms move from being single celled to multicellular they were able to get bigger for this reason so this is a very very important concept in biology if you look at this picture and look at surface area to volume ratio you can see we have this one tiny cell okay so imagine this is a single-celled organism such as a bacteria that bacteria can't get this big that wouldn't work look at the surface area to volume ratio it doubles it would be really tough for materials to diffuse all the way to the center of that organism but look if we if we have something that's really the same size as this big block but it's made of a lot of little blocks each of those little blocks has the same surface area to volume ratio as this original so this is a good plan it just shows you organisms could get bigger by having a lot of little cells and that's what organisms did when they became multicellular those cells were small this really summarizes a little bit of what i said a minute ago as the size of the cell increases the volume increases faster than the surface area and if you have too much volume that means you can't move materials to the middle of the cell okay things won't move as efficiently by diffusion if that cell is has too much volume relative to the surface area so that means when you do the math if the surface area is smaller relative to the volume then that surface area to volume ratio decreases if you have a large surface area in a low volume you have an increase in diffusion rate so this would be small cells okay so small cells have a large surface area in a small volume great diffusion rate but as the surface area gets smaller relative to volume you have a decrease in diffusion rate so this would be large cells this is not a good plan you actually have a lab activity based on this concept so this is a very important concept to understand the cell structure and function lab activity number one requires you to cut potatoes into little chunks and those are going to simulate cells and you're going to put them in iodine and you're going to look at the diffusion rate of the iodine so cell surface area to volume ratio is a very important concept to understand not just in lecture but you'll be demonstrating that in lab so if you have questions about that be sure to ask looking at entire organisms that are multicellular this is also an important concept so this is a flatworm and flatworms are pretty primitive in structure they don't have a vascular system to move materials around materials move mostly by diffusion so gas exchange from the outside environment to the inside of the organism occurs a lot based on simple diffusion and so this worm cannot get fat so this worm has a large surface area as you can see in the picture a relatively large surface area and small volume and that equals good diffusion materials are going to be able to move around more easily through this organism these organisms cannot get fat they can't get a big volume they have to be flat in order to be efficient more advanced worms such as this earthworm this is actually a very advanced forum so this worm is segmented he has specialization of those segments and has actually a very complex vascular system because of that vascular system this worm is able to be fatter okay so this worm has a lower surface area and larger volume the only way this worm can achieve that is because it has a complex vascular system to move materials around it's not just relying on simple diffusion so that's another strategy that organisms used as they became more complex and started specializing different regions of their body to have a vascular system to move waste products around move gases nutrients hormones whatever needs to move through the bloodstream that vascular system is going to enable that organism to become bigger and become more complex again surface area to volume ratio very important when looking at cells looking at eukaryotic versus prokaryotic cells we've talked a little bit about the basic differences before remember the big difference is a nucleus but there are some other differences we're going to see also as we start looking you can see already just looking at this picture that eukaryotic cell is much more complex in structure compared to that prokaryotic cell we're going to look at that in more detail okay so this is a basic prokaryotic cell in fact this is a bacteria cell and the first thing that you'll notice is that this area called the nucleoid region replaces what would be called the nucleus in a eukaryotic cell so this is the region where the cell has its dna but it is not protected in a membrane you're going to see when we look at the eukaryotic cell that the nucleus is defined by what's called the nuclear envelope so prokaryotic cells and i'm just going to say prokaryotes no nuclear envelope dna is just free in the cell okay a lot of students get confused and think prokaryotes don't have dna they have to have dna to be a living organism okay that's how they code for their proteins just as more complex organisms do so they have dna it's just not protected in a membrane it's just free in the cell and that area that region where the dna is located is called the nuclear nucleoid region also no membranous organelles organelle means tiny organs okay so when we look at the more complex eukaryotic cells you're going to see a lot of organelles made of membrane so they're called membranous organelles prokaryotes don't have membranous organelles in fact the only real internal structure that they have is they do have ribosomes so only true organelle are the ribosomes and the ribosomes are where proteins are assembled so ribosomes we talked about a little bit when we talked about nucleic acids ribosomes are where proteins are assembled so right here you can see ribosomes and these are organelles that synthesize proteins this is the assembly plant for proteins in eukaryotes and prokaryotes so if i were to draw a simple diagram of a bacterial cell that's a little less messy than that one this by the way is not the shape of all bacteria okay this is a rod rod-shaped bacterial cell they're called bacilli we'll learn more about the the three possible shapes of bacterial cells later in the semester not all bacteria have this shape but they all have on the outside here this plasma membrane which you'll see in eukaryotic cells also okay and then they have this circular piece of dna that wraps around itself a lot of times but it's basically one circular piece of dna and this is what's called the chromosomal dna this codes for all necessary proteins in the bacterial cell sorry i just spelled that wrong chromosomal sorry i'm really messing this up now chromosomal dna it codes for all the required proteins in that bacterial cell the reason we make that distinction is because a lot of bacteria also have some additional dna a little ring of dna and they can have more than one and this is called the plasmid dna and we'll talk about this more later in the semester i'm just going to point it out now now as i mentioned the only other true organelle in the cell are the ribosomes and i'm just going to draw those as little circles no membranous organelles in this bacterial cell i'm gonna oh boy sorry about that as we get close to the edge it just doesn't do well i'll draw them here okay and then this is important too on the outside of that bacterial cell is a cell wall now we learned about the cell while when we talked about carbohydrates remember the cell wall implants is made of cellulose which is a polysaccharide it's a structural polysaccharide so it's a chain of glucose that makes up the cell wall of plants the cell wall of this bacterial cell though is made of something different okay so here's the cell wall outside the plasma membrane and when we talk about bacteria in more detail you'll learn what that cell wall is made of later in the semester okay and sometimes they have a flagellum to move on sometimes multiple flagella for locomotion so there are these tail-like structures you can also have these little structures on the outside called pillai this is how they stick or attach the surfaces so for example that's how bacteria attach inside your digestive tract in your colon and your intestines the bacteria that are really really important to your your gut health and your overall health will learn a lot about your microbiome later in the semester and that's how they attach is with those pillow that's how bacteria attach to surfaces in your house is with these little sticky structures but otherwise very very simple in structure some actually have a capsule outside the cell wall that makes them even more resilient so things like anthrax and and botulism the reason those are so resilient is they have this capsule on the outside of the cell wall that makes them even tougher to kill so they're resistant to uv radiation heat cold so prokaryotes very simple in structure no nuclear envelope the dna is just free in the cell they're all single celled no multicellular prokaryotes if something is single celled it means the entire organism is made of just one cell no membranous organelles the only true organelles or tiny organs in the in the cell are the ribosomes and those have the same function that they do in eukaryotes they're involved in a simile of proteins plasma membrane cell wall that's it eukaryotes obviously are a lot more complex okay so this is an animal cell and this is a plant cell and you can see a lot more going on in these cells we're going to talk about the similarities and differences just very briefly okay we're going to talk a little bit about the the similarities and differences between animal cells and plant cells for the most part plant cells have all the same structures as animal cells overall so the main ones we're going to talk about in this class are shared one of the big differences is that plants have this structure called the chloroplast and the chloroplast is where photosynthesis occurs you're going to learn about photosynthesis in more detail that's how plants take light energy from the sun and make carbohydrates to use for cellular respiration because plants don't eat so very very important most important chemical reaction on earth is photosynthesis no life on earth would exist without photosynthesis and we will talk about that also you see this plant cell has something called a vacuole and that vacuole here is involved in water regulation and animal cells don't have that plants need water to carry out photosynthesis in fact water is the first reactant that enters photosynthesis so that is involved in in water regulation in the plant cell those are two struct animal cells do not have otherwise all the main structures are the same rough and smooth er golgi ribosomes lysosomes mitochondria plants and animals have those structures plants of course have a cell wall and you can see that cell wall on the outside of the plasma membrane in this plant cell and remember that cell wall is made of cellulose which is a carbohydrate it's a chain of glucose it's a structural polysaccharide animal cells don't have that so if we look at the list here of what they share you can see that they both have all of these structures that we're going to talk about today so don't worry if you don't know these terms yet we're going to go through all of these today animal cells no cell wall we just talked about that for the most part no vacuole okay no chloroplasts and some animal cells can have a flagellum to move but plant cells don't have that okay let's start looking in more detail at the individual structures in the animal cell sorry i dropped something hold on one second okay sorry i'm back okay so this is the nucleus and the nucleus of the cell is defined by the nuclear envelope that surrounds the nucleus so the nucleus really is more of a i like to think of it as a region of the cell but it's a structure that's defined by the nuclear envelope so if you look at a typical cell i'm just going to draw one here and the center would be the nucleus it doesn't have to be exactly centered though and it's really the nuclear envelope that defines that nucleus okay and then inside that nuclear envelope is the dna so that nuclear envelope is protecting the dna from the rest of the cell from all that chemistry happening out in the cell this region outside the nucleus between the nuclear envelope and the plasma membrane is called the cytoplasm and again the cytoplasm is really more of a region of the cell that's an l sorry it won't get bigger than that so this whole region is the cytoplasm between the nuclear envelope and the plasma membrane so we have the nucleus defined by the nuclear envelope and then we have the cytoplasm so if we go back to this big diagram this whole region here this would be the nucleus okay and this whole region here is the cytoplasm so there's a lot going on in the cytoplasm that's where all of these other structures exist so the nucleus is only just that small region not exactly centered but we usually say it's in the center of the cell and again it's defined by the nuclear envelope that's where the where the dna is protected from the rest of the cell materials can move in and out of the nucleus through what are called nuclear pores and these nuclear pores are openings in the nucleus and you can see them here all these little nuclear pores and here's one blown up i love this electron micrograph over here showing the nuclear pores okay so nuclear pores how materials enter and leave the nucleus when we start talking about transcription and translation you're going to see that messenger rna is made in the nucleus okay we make that copy of one gene in the nucleus and then that messenger rna leaves the nucleus through a nuclear pore and comes out to the cytoplasm where a ribosome assembles around it to make the protein so nuclear pores are how materials move in and out of the nucleus you'll see that attached here is this membranous structure and it's the first membrane structure we're going to talk about called the endoplasmic reticulum and you can see that it's contiguous really with a nuclear pore so there's a lot of communication between the outside of the nucleus and the inside of the nucleus through these nuclear pores but it's really the nuclear envelope that is defining that nucleus and again the dna is all inside here inside the nucleus being protected from the rest of the cell ribosomes again we've talked about a little bit when we talked about proteins and nucleic acids and we just talked about them a little bit when we talked about the bacterial cell now here they are we have two types of ribosomes in a typical eukaryotic cell they're what are called free ribosomes and what are called bound ribosomes okay so the free ribosomes are just free in the cell and you can see all these free ribosomes out here they're not attached to anything the bound ribosomes are the ones that are connected to this membranous structure called the endoplasmic reticulum it's abbreviated er endoplasmic reticulum it's a membranous structure that can take one of two forms that we're going to talk about in a minute but the difference in these two ribosomes is significant they're both involved in protein assembly so this is where the messenger rna recipe is read in the ribosome and is translated into the amino acid sequence of the protein okay so this is where all of the amino acids are strung together to eventually make that polypeptide chain that folds into the final protein the difference is that free ribosomes that are just free in the cell this is where we assemble proteins that remain in the cell okay so for example key enzymes that are needed for that cell to carry out its chem its chemistry all of its chemical reactions require enzymes and we make those enzymes on free ribosomes that are just loose in the cell salt free in the cell not attached to er we also have what is called bound ribosomes or what are called bound ribosomes and these bound ribosomes are attached to what's called the rough er the rough endoplasmic reticulum those bound ribosomes are attached to the rough endoplasmic reticulum and this is actually a pretty good setup and i'm going to show you why so if this is a typical cell and here's the nucleus and then attached to this nucleus we have some endoplasmic reticulum membranous sacs and on the endoplasmic reticulum we have some ribosomes okay remember there's some free ribosomes in the cell that's where we're going to make proteins that stay in the cell but then attached to this membranous er are some other ribosomes if we blow up that er i'm going to blow it up bigger sorry blow up that er right here here are the little ribosomes on the outside what can happen is the cell can start making a protein make it green it can start assembling a protein and that protein can start feeding into the inside of the er so here's the proteins getting assembled here just to make a little blob and now a piece of this er can pinch off carrying that protein product okay so here it's going to pinch off and now it's going to be this separate little sac and it's going to be carrying that protein product here in the middle there's our protein in the middle this is a very handy setup if we need to export that proteins so those bound ribosomes those are involved in assembly of proteins for export let me erase this part so attached to rough er and they're involved in assembly of proteins for export again this is a really good setup the protein as it's being translated feeds into the lumen here a piece of that membrane pinches off carrying that protein product and now that can move eventually to the the plasma membrane and leave the cell and we're going to see how that happens so if a protein needs to be exported it's going to be made on the er and it's going to be packaged in that piece of membrane a membranous sac carrying a product in the cell that pinches off from the er or the golgi or another membranous structure so here's that membranous sac and it's carrying that protein product so here's the protein inside there this is called a transport vesicle a vesicle is just a membranous sac a sac made of membrane so vesicle is a membranous sac a sac made of membrane and if it's a transport vesicle it means it's a vesicle carrying a cell product that transport vesicle just pinched off from the rough er carrying that protein product so that's a very handy setup we're going to see what happens later um to that product okay this is a ribosome blown up by the way it's not just this little circle you can see there's a large subunit and a small subunit and you're going to see that the messenger rna is going to feed through this ribosome and get translated into a protein and you'll see how that happens later in the semester okay so free ribosomes bound ribosomes the bound ribosomes are on the rough er so that is the function of the rough er it's involved in protein assembly four proteins that get exported from the cell so for for example we've talked about insulin okay insulin is a protein hormone insulin is made in the pancreas doesn't do us any good if it stays in the pancreas it needs to get out of those pancreatic cells and into the bloodstream to allow us to regulate our blood glucose levels the way that happens is it's made on rough er in those pancreatic cells and then it's packaged in a transport vesicle pinches off from the er and that's going to move through the cell and eventually that product is going to leave the cell and we'll see how that happens there's another type of er called smooth er so you can see here in this picture the rough er has ribosomes the smooth er does not have ribosomes smooth er in fact has completely different functions i'm just going to quickly tell you about a couple of functions of the smooth er so the smooth er does not have ribosomes it looks smooth under the microscope versus the rough er looks rough because it's covered in those ribosomes so functions of the smoothie are okay the smoothie art is involved in detoxification so drugs alcohol other toxins that come into this to the body the smooth er in certain cells of the body detoxify they attach functional groups to those molecules that allow them to be more easily flushed out of the body they make them more water soluble so we get rid of them more more easily if you take a certain medication or you drink alcohol over a long period of time you develop more smooth er and you get better and better at detoxification and you develop what's called drug tolerance and that is because of the smooth er so you know think back to if you are 21 and you drink alcohol you know the first couple of times you drink alcohol you get you feel it right but over time you build tolerance and that's because of your smooth er so your cells are going to make more smooth er and get better at detoxifying and then if you stop drinking your body is going to recycle what it's not using so a lot of that smooth er in the cell will get recycled the parts will get broken down used to build other structures and over time you'll kind of go back to that same set point again but detoxification is an important function of the smooth er so what organ do you think in the body would have cells that have a lot of smooth er where where in the body do you do most of your detoxification your screen it's about to there we go that's so strange so liver cells are involved in detoxification they would have a lot of smooth er by the way you can tell a lot about a cell's job by looking at the amount of organelles of a certain type that it has so cells don't have what they don't need so a cell packed full of rough er would be a cell that's really involved in making a lot of proteins for export so cells of the pancreas that make insulin or glucagon those are protein hormones made for export those would be packed full of rough er cells of the liver that are involved in detoxification would be packed full of smooth er so that's one function of the smooth er i'm not going to give you all the functions today lipid synthesis okay assembling certain types of lipids okay so this is where phospholipids would be assembled this is where the lipid-based cholesterol based hormones are assembled and remember that included cortisol or stress hormone it included estrogen testosterone progesterone so the the sex hormones okay so cells of the ovaries that make estrogen would be packed full of smooth er whatever that cell's job is it's going to have a lot of that organelle to perform that job so cells of the ovaries that make estrogen would be packed full of smooth er cells of the testes that make testosterone would be packed full of smooth er okay i'm just going to give you one more function of the smooth er even though there are more than this third function sorry this blood is getting really messy third function calcium ion storage and release and this is really involved in muscle contraction so your muscle cells have a lot of smooth er in fact the smoothie are of the muscle cells actually has a special name it's called the sarcoplasmic reticulum and this is the smooth er of your muscle cells if you go on to take anatomy and or physiology you'll learn about the sarcoplasmic reticulum so that's a third function of the smooth er again totally different functions than the rough er different enzymes embedded in that membrane but just as a product of the rough er can pinch off in a transport vesicle the same thing happens in the smooth er okay so let's say this is our smooth er and let's say this is in the ovaries and a lot of estrogen hormone is made and now it needs to get out of the cell a piece of that will pinch off into a transport vesicle carrying that hormone product just as we saw with the rough er okay the golgi this is another membranous structure in the cell this is a stack of membranes that are really involved in processing products that were made in the er so you can see this transport vesicle right here carrying a product and it carries it to the golgi and now that product enters the golgi and it's going to move through these stacks of the golgi i really mess that up where you can't see it very well it's going to move through the stacks of the golgi and it's eventually going to come out the other side so there's kind of a receiving side of the golgi and a shipping side of the golgi but what happens is those products get modified so the golgi is involved in modification of products and eventually labeling those products for export this is sometimes known as kind of the ups center of the cell where those products come out the other side in a new transport vesicle and now they have some sort of tag telling them where to go there are some other important product functions of the golgi but just know that they're involved in product modification and labeling for export we won't talk in detail about the other functions of the golgi one more memberness organelle that i'm going to tell you about in a minute but i'm actually going to skip that slide and go to this picture all of these membranes in the cell work together through what's called the endo meaning inside the cell endo membrane system you can see the nuclear envelope the rough er the smooth er those transport vesicles the golgi all work together and eventually the plasma membrane is involved too and what's important to realize because we're going to see this theme in particular when we look at the plasma membrane it's important to realize that membrane fuses with other membrane remember that membrane is mostly phospholipids and that doesn't just include the membrane on the outside of our cells the plasma membrane it also includes all of these membranous organelles so whenever we say membrane we're talking about mostly phospholipids with some key proteins involved too but a lot of phospholipids and those membranes can all fuse with each other so that's how that transport vesicle can pinch off from the rougher smooth er carrying a product it can fuse with the membrane of the golgi and then a new transport vesicle can pinch off the other side as you see here and then you see it moves to the surface of the cell where it fuses with the plasma membrane and here we see that that's going to open up and release that product out of the cell i'll go ahead and give you this term now we're going to talk about it in more detail in the video about the plasma membrane and that term is exocytosis and this is materials leaving the cell okay through fusion of a transport vesicle with the plasma membrane so that transport vesicle moves to the plasma membrane and those materials leave this out so that could be a protein that was assembled on the rough er it could be a hormone such as cortisol estrogen testosterone that was made in the smooth er and that transport vesicle is going to carry that to the plasma membrane and then it's going to leave the cell through what's called exocytosis you're going to learn that we can also bring materials into the cell by wrapping plasma membrane around bringing it in through what's called endocytosis so when we learn about transport across the cell membrane you're going to see endocytosis is the opposite that's wrapping something in membrane and bringing it in so the endomembrane system is incredibly important in the cell the one structure i didn't tell you about are the lysosomes and lysosomes have a lot of really important functions but one thing that they do is they recycle old cell parts so all the structures in your cell have a life span we want to reuse those parts to build other structures so those all get digested so really the the lysosomes are a sack of hydrolytic enzymes do you remember what hydrolytic means we talked about hydrolytic enzymes when we talked about ph and the digestive system and remember in that intro to organic chemistry lecture we learned about a specific chemical reaction that breaks down big molecules into smaller molecules and remember that was called hydrolysis so hydrolytic enzymes carry out hydrolysis so what lysosomes do is you can see here the lysosome is in purple and it's going to fuse with this old mitochondrion that's being carried by transport vesicle look membrane fuses with membranes so this transfer vesicle is made a membrane so is the lysosome they fuse together and then those hydrolytic enzymes are going to digest that other cell structure and then spit out the parts lysosomes are actually involved in cellular eating as well so single-celled organisms such as protists they use lysosomes to digest their food so you can see here food comes in it gets wrapped in membranes so this would be endocytosis it gets brought into the cell wrapped in membrane membrane fuses with membranes so this membrane is going to fuse with the lysosome and the lysosome is actually full of hydrolytic enzymes that are going to digest those food particles this is also how certain of our white blood cells work so we have some white blood cells called phagocytic white blood cells you'll learn what phagocytosis means it's a it's a term that's a very specific form of endocytosis but those phagocytic white blood cells use lysosomes to digest pathogens so the lysosomes are going to be an important part of your white blood cells being defensive in other words breaking down foreign particles dust dog hair things we breathe in so we'll have phagocytic cells in our lungs that break down those foreign materials they can actually kill bacteria and other pathogens that get in parasitic worms okay through either emitting different chemicals but that's another way that certain white blood cells do where they actually devour it's called cellular eating they actually bring in that foreign cell so they can devour a bacterial cell and use their lysosomes to break that down so if you get a splinter in your finger bacteria get into your skin these phagocytic white blood cells are going to come devour that bacteria and use their lysosomes we also use lysosomes to do something that's called apoptosis it's spelled apoptosis and this is when entire cells digest themselves so there are certain times when an entire cell would need to digest itself if there's a dna mutation if that cell has been invaded by a virus we're going to learn about different ways that that happens later in the semester but that is one of the rules of the lysosomes is digest that entire cell when you're developing you actually have webbing between your fingers and lysosomes in those cells of your skin are signaled to digest those skin cells that are between your digits so at some point that webbing is digested some people have a genetic mutation that allows some of that webbing to stay and you can look at those pictures on the internet if you're curious okay so life systems it's a sack of hydrolytic enzymes it can digest old cell organelles it can be used for cellular eating including in our white blood cells and it can be used to digest entire cells if we need to destroy an entire cell it's called apoptosis another term for apoptosis is cell suicide where all the lysosomes open up and digest that entire cell okay lysosomes very important i know this is a long lecture we're getting close mitochondria okay these are not part of the endomembrane system in fact mitochondria are pretty unique this is where most of our atp is generated during cellular respiration so mitochondria are where most of our cellular respiration takes place this is where atp is produced so mitochondria are involved in atp production through cell respiration you're going to learn a lot about that you're going to learn about the detailed structures of the mitochondria there's an inner membrane an outer membrane a matrix an intermembrane space you don't need to know those structures now the reason they're just shown on this diagram is realized when we learn about cell respiration different stages of cell respiration are going to take part in different regions of the mitochondria so there is some complexity of structure there that you will need to know in the future mitochondria are really really unique they act almost as independent organisms so let's talk a little bit about what those unique characteristics are that make them like independent organisms but i also want to point out that mitochondria have their own ribosomes they have their own mitochondrial dna and if you look at this mitochondrion not only does it look like a bacterial cell but it actually functions a lot like a bacterial cell and it's pretty well understood in biology today that mitochondria used to be independent organisms and they were taken in by other bacterial cells and became symbiotic it's called the endosymbiosis theory and it applies to both mitochondria and chloroplasts so you can see an ancestral eukaryotic cell that really wasn't able to very efficiently produce energy you're going to see that some of our atp is made in the cytoplasm but most of it is made in the mitochondria and at some point these bacteria were ingested by the cell and now there's this symbiotic relationship between these structures that used to be free living bacteria so rather than the cell digesting them it allowed these bacteria to live in the cell and now they serve really important functions so really the the endosymbiosis theory includes um mitochondria sorry every time i touch this with my hand it does something crazy and it's impossible to write on the screen without touching with my hand and i know there's a setting where you make it only work with the pencil and i've got that turned on and it still is so mitochondria and chloroplasts are part of the endosymbiosis theory they both function as independent organisms they have their own dna they divide independently from the rest of the cell mitochondria even have their own ribosomes so they make their own proteins let's talk a little bit about that okay so if you look at that mitochondrial structure we mentioned before that they have their own deal they have their own dna it's called mitochondrial dna and we're going to talk more about that in a second they have their own ribosomes and so they can make their own proteins unique features they divide independently independent of the rest of the cell they make atp so essentially they can make their own energy okay obviously they have dna and they can make their own proteins that really meets the definition of a living organism if you think back to the very beginning of the semester when we talk about what makes a living organism mitochondria act just like living organisms and in fact that mitochondrial dna looks very much like bacterial dna and encodes for a lot of the same traits so we're you know we're very sure this endosymbiosis theory to reach the level of theory in science remember that's a big deal that means it's been supported by considerable evidence lots of of data has been collected by many many many people over many many many years to reach the level of theory so it's pretty cool also important to realize that you get your mitochondrial dna only from mom okay your chromosomal dna half is from mom and half is from dad but you get your mitochondrial dna only from mom so when egg and sperm unite here's the egg and in the nucleus of the egg you have 23 chromosomes and out here are the mitochondria i'm just going to make little squiggles in the middle so here are your mitochondria in the egg here comes the sperm okay it also has 23 chromosomes in the nucleus but guess where the mitochondrial um where the mitochondria are on the sperm they're mostly all on the tail and they don't become part of that first cell so when those two fuse they form that very first cell of 46 okay 23 from the egg that made you and 23 from the sperm and all the mitochondria of that very first cell came from the egg and this divides and divides and divides to make grown up you and every single one of your cells has mitochondria only from the egg so all from mom so all mitochondria are from mom which means all of your mitochondrial dna is from mom if you've ever watched a crime show you know you can leave mitochondrial dna just as you can chromosomal dna obviously every single cell has millions of mitochondria so mitochondrial dna is easier to find sometimes than chromosomal dna the only way someone on this planet has your same chromosomal dna is if you have an identical twin otherwise everyone's chromosomal dna is slightly different but we have a lot of similarity in our mitochondrial dna because if you think back to the very first homo sapiens that same mitochondrial dna has been passed down generation to generation to generation you know they have what's called the mitochondrial eve whoever the first human is that gave us our mitochondria we all have really similar mitochondrial dna now obviously there have been some mutations over time that have occurred but for the most part it's very similar and that's true for all animals and so you can trace relationships among animals based on similarity of their mitochondrial dna so evolutionary biologists use mitochondrial dna to trace relationships among organisms so that's pretty cool too mitochondrial dna is really really interesting and you can see it's circular dna just like bacteria have okay chloroplasts you're going to learn a lot about when we talk about photosynthesis so this is only in photosynthetic organisms and it's not just plants okay photosynthesis occurs in certain photosynthetic bacteria that have chloroplasts it include includes the photosynthetic protists that have chloroplasts and of course it includes the plants so not plants aren't the only cells that have chloroplasts we're going to mostly talk about the plants okay but there are photosynthetic bacteria and photosynthetic protists that came before the photosynthetic multicellular plants plants are multicellular okay produce and bacteria are all single celled the difference is that protists are eukaryotes and bacteria are prokaryotes but these chloroplasts are where photosynthesis where photosynthesis occurs in all of these different organisms sorry this is multicellular but again toward the edge i don't even know why i haven't learned yet to not write toward the edge because you just can't read it sorry um peroxisomes are an organelle in certain cells i only have this on here because we have an enzyme lab later in the semester that involves peroxism sorry i'm just going to quickly plug this in because i'm getting the signal that my ipad is getting low um peroxisomes carry out an important reaction that we're going to study in the enzyme lab and what peroxisomes do is they take hydrogen peroxide which is a product of a lot of chemical reactions in the cell h2o2 and they convert it to water and oxygen water and oxygen okay not toxic obviously you have a lot of water and oxygen in your body and it's not toxic okay this is hydrogen peroxide and it is toxic so peroxisomes are involved in making that conversion from this toxic hydrogen peroxide and if the peroxisomes are working they have an enzyme called catalase that breaks down that hydrogen peroxide into water and oxygen and you'll see the oxygen makes bubbles and that's why when you put hydrogen peroxide on your skin it causes bubbles because the catalase in your cells is breaking down that hydrogen peroxide into water and oxygen and it actually is destroying the the membrane of any bacteria that are there so that's why we use it but you'll see those bubbles as the oxygen is released so again the only reason i have these peroxisomes on here is because catalase enzyme and hydrogen peroxide we're going to study that in the enzyme lab we're going to actually use yeast um and yeast have catalase enzyme and can do this same thing we're going to look at hydrogen peroxide and how it's processed by yeast the cytoskeleton is important to understand because we're going to look at different functions of the cytoskeleton especially when we study cell division there are several elements of the cytoskeleton so if you look at this slide you can see they're what are called microtubules there are microfilaments and intermediate filaments really the only one you need to specifically know the name of are the microtubules right here and that's because when we talk about cell division the microtubules are actually going to pull the two sister chromatids apart or if we're talking about meiosis they're going to pull the homologous chromosomes apart and eventually the sister chromatids apart so the microtubules which are part of the cytoskeleton are going to be involved in cell division which is one of the functions of the cytoskeleton but as far as um microfilaments and intermediate filaments you don't need to necessarily know those terms but what i do want you to know is i want you to know kind of a list of functions of the cytoskeleton so the cytoskeleton is really filling the whole interior of the cell that's not filled by those other organelles and so looking at functions of the cytoskeleton you know i want you to realize there's not really a whole lot of free space in the cell and things don't like free flow like gelatinous blobs through a cell they move on this transportation network called the cytoskeleton so let's look at some different functions of the cytoskeleton and i'll probably have to erase a couple times because i don't have much room here cell structure and shape are one of the functions of the cytoskeleton the cytoskeleton is what gives a cell its specific shape and really holds that structure in shape it also anchors the organelles in place so nothing is really free-floating in the cell it's the transportation network so for those transport vesicles they don't free float from the er to the golgi they move along this transportation network called the cytoskeleton and then when those transport vesicles need to move to the plasma membrane to get materials out of the cell or move materials into the cell those materials all move those transport vesicles move along elements of the cytoskeleton okay they're involved in so this would be movement of materials inside the cell they're also involved in movement of entire cells okay so flagella are extensions of the cytoskeleton and as we said before involved in cell division and you're going to see how that happens that's the microtubules in particular there are other roles of the cytoskeleton but that's that's a pretty good list of what you should know and again you don't need to know when the microfilaments do this and the intermediate filaments do this just know that these are some functions of the cytoskeleton okay that's finally it for the cell you