hi everyone this is chapter one part three of cell structure where we'll be talking about cell structure and function mostly organelles really now in cell structure and function first of all we kind of need to define a few terms when we say organelles what do we mean we usually mean functionally and structurally distinct part of a cell that's surrounded by membranes that's like separate from one another it has a separate specific function like say the nucleus from the rough and the plastic reticulum these are surrounded by their brains and they're like separate functions now ultrastructure is kind of more general it's not necessarily surrounded by midbrains sometimes it's just detailed structures of a cell kind of like the cell membrane the cell membrane we don't usually look at it as an organelle it's a cell surface membrane around the cell it's an ultrastructure instead of an organelle so yeah now under cell structure function there are actually a few things we need to talk about there are prokaryotes and eukaryotes okay the whole world all the organisms in it can be mapped onto a tree of life and there are two major types prokaryotes which consists of bacteria and archaea later on in this chapter we go into bacteria a little bit but right now we are looking at congrats where we are at we are animals we are somewhere in this category of mammals here um and there are plants under eukaryotes as well and we are talking about these types of cell first eukaryotic cells with eukaryotic cell structure first now talking about eukaryotic cell structures planted animal cells included you need to do three main things number one you need to name it when you see it okay in any diagram you need to don't name it until you need to recognize it from any diagrams or micrographs they may throw at you and you need to know its functions there are quite a few you kinetic cell structures you need to know about these are the 16 types and today we'll be covering nine types one up to nine let's go number one there is cell surface membrane again cell surface membrane is not really an organelle it's like an ultrastructure you can see under the electron microscope it kind of looks like this um it is also called the plast mom and brain it is around seven nanometers thick again being able to see it under the electron microscope not so much the light microscope and under the uh electron microscope at 100 000 times it will be seen as three layers and therefore we say that it gives tri-laminar appearance now the appearance is due to this phosphor lipid by layer it is made out of so it looks like a sandwich perhaps like one layer two layer three layer kind of situation but really it's a phospholipid bilayer there's only two layers of it this is one phospholipid this is a phospholipid bilayer anyway it's partially permeable so not all substances can freely move in out the cell because its function is to be on the outside and control movements of substances into and out of the cell you will be learning a lot of detail about the cell surface membrane and its structure in chapter four moving on to the next organelle nucleus the nucleus is a famous organelle you should know this by now but do you know it is the largest organelle and the most visible it's present under a light microscope it has double membranes by the way this means it has two phospholipid bilayers two two and well it's general function really is to contain a lot of genetic information and keep it kind of separate from the cell because the cell may have a lot of reaction so the nucleus kind of contains this dna to the information for what for the synthesis of protein now the dna inside the cell will be transcribed into mrna there is a new word for you it go undergoes a process of transcriptions it gets converted to mrna and this mrna is then translated into proteins later on in the cell not in the nucleus but somewhere else in the cell now this uh dna as i mentioned just now is in the nucleus and protected inside now that's not it okay that's not it this is a general function but within the nucleus there are also more ultra structures besides the nuclear envelope which is the membrane that is kind of outside the nucleus on the surface uh you must know that this is attached to er by the way er endoplasmic reticulum is made of two membranes again two phospholipid bilayers uh this nuclear envelope also has nuclear pores by the way and these parts are how substances move out and in of the nucleus and cytoplasm so it's kind of like the cell surface brain but for the nucleus controlling movement of substances is incredibly important because it controls function right controlling movement means controlling function there are proteins there are mechanisms in place to direct that control anyway that's a nuclear envelope that has more detail that i thought you would have the second part is the nucleolus nucleolus is the densest region of the nucleus and really it's the site of ribosomal rna synthesis so other than normal messenger rna the nucleus also generates produces ribosomal rna which you guessed it it's used for chromosomes right it is the site of ribosome assembly ribosomes are assembled and then it can be used later in the cell last but not least there's chromatin and chromatin is basically what we call dna and it's proteins because i know we imagine dna as this double helix but honestly in the cell dna is often associated with proteins means imagine a double helix they are kind of wrapped around proteins called histones and you'll be learning more about histones and dna packaging later on in your a levels as well specifically it's in chapter six anyways that is the new class for you there's the nuclear envelope there are nuclear pores which is part of an england envelope new clearness and chromatin let's talk about ribosomes next well as we know the nucleus has dna it gets transcribed into mrna and the mrna actually exits the nucleus and it actually goes into the cytoplasm the cytoplasm in the cytoplasm there are ribosomes where translation occurs and converts right translates that mrna into protein ribosomes as we know from previous videos is the smallest organelle it is only 25 nanometers in size it is not bound by a membrane and it's one of the only organelles not to be bound by a membrane this is the exception now it's made of rrna which is synthesized in nucleolus that we saw just now and also some other protein it has two subunits as we can see here a large subunit and small subunit it's usually simplified diagram in this manner here now its function as we can see in this picture in my explanation just now is to produce protein it is the site of protein synthesis and you can see here how it can also sit on the rough endoplasmic reticulum you can see how the mrna passes through it and the amino acids are assembled into a protein a polypeptide chain a protein in a certain way cool right now there are two types of ribosomes actually the ones that i've been talking about is the ats ribosomes they are 25 nanometers this is the normal ones in the cytoplasm and rough endoplasmic reticulum of all eukaryotes however there are such things called 70s ribosomes and 70s ribosomes are smaller you don't remember the size here you just need to know they are smaller and they are found in the mitochondria and chloroplasts of eukaryotes can you believe it right there's ribosomes in your cytoplasm and rough in the plasma response and there's also ribosomes but a smaller one a different type in mitochondria and chloroplasts after eukaryotes and of course in prokaryotes they also have 70s ribosomes they are just a bit smaller s is actually a kind of unit for size this week is that number four endoplasmic reticulum rapid no plastic reticulum more commonly known as r-e-r because i'm too lazy to say the whole thing the mouthful okay as we know from just now it's an extensive connected system of membranes that's actually connected to the nuclear membrane now it's extensive critical criticism of membranes so it's connected again with the nuclei and verb it's called cysteine cysteine systole means flattened membrane stacks and don't you think it looks like that it's like membrane membrane squish like long that thing became longer anyways it runs through the cytoplasm um and it gives it has a rough appearance because there is ats ribosomes attach its function mainly is for protein synthesis but the rough endoplasmic reticulum also can help in protein modification to some extent very simple ones like protein folding or glycosylation which is the addition of carbohydrate chains for protein which is actually a very common um process to modify your proteins yeah energy they also transport this protein after it's synthesized to goji for more modification now let's talk about its sibling smooth endoplasmic reticulum what gives it that appearance is the absence of ribosomes now it's continuous also by the way with the rough plasma rough endoplasmic reticulum and you can see it in this three-dimensional really cool picture here that they are really all connected the nuclear envelope a rough endoplasmic reticulum a smooth endoplasmic reticulum we just get a cross-section really but really they're all connected anyways what is function form now rough endoplasmic reticulum is mainly for the synthesis of of protein but smooth endoplasmic reticulum is mostly for lipid and steroid synthesis examples of this include cholesterol steroidal hormones etc so yeah that's all you need to know now back to uh the protein bits so r e r graph endoplasmic reticulum like synthesizes proteins and it modifies them a little bit sometimes and it transported to the goji right so let's talk about the goji my students call this wi-fi it doesn't look like wi-fi a little bit like inverted but anyways the golden body is a little bit separate actually from the er so it's a little bit further from the nucleus that's how you kind of guess that it's the golgi body and the electron micrograph it's also made of cisternae like er which is flattened membrane sex but again separate this continuous from the nuclear envelope endoplasmic reticulum and so on so above now what is special is also there's no connection between members of itself so unlike endoplasmic reticulum these members are kind of separatish and it has swellings at the end of the sex for physical formation that's this is because it's because it's constantly being formed and broken down by these physicals it's being formed by transport vesicles from the rough endoplasmic reticulum on the cis phase as being broken down to form continuously to form secretory vesicles and lysosomes on the tron's face and what this means is that it's forever like evolving and moving now i'd like to like kind of describe it to my students as like um like the white microbots in big hero 6. i don't know if you watch big hero 6 but basically it's like a bunch of tiny robots that can become whatever they want and they can fuse and they can split from each other and they can make monsters or they can make like separate tiny monsters i don't know but they're quite useful and actually the goji characters kind of functions like that basically all membranes function like that because if you think about it all membranes are made of phospholipid bilayer right and this phospholipid bilayer can kind of like butt off and form something on its own but it also willingly fuses and forms mergers to form something else so this is kind of like that transport vesicles like fuse to form pathogen and particles you have butts off breaks down to form other vesicles and lysosomes into smaller components in order for other things a little bit more about goji body um let's talk about the function so why is it like constantly butting off and you know like fusing in what is the function number one is for modification mostly of both proteins and lipid for example glycosylation okay some uh overlap in function with the endoplasmic reticulum that's okay our body loves redundancies like basically like overlapping function that is okay phosphorylation additional phosphate groups that is a very common modification as well uh as well as the cutting and folding of proteins so the golgi bodies would probably have quotes enzymes in order to carry these things out next packaging molecules into vesicles for transport so the proteins come from the er to transport vesicles and then after it's modified maybe this molecules can be packaged okay this protein all lipid can be packaged into trans sorry secretory vesicles uh for release of protein maybe out of the cell or also secretory vesicles to place proteins at the membrane of the cell other than that there's also a budding off to form lysosomes which contain proteins those proteins are enzymes called lysosome signs we'll talk about that later now let's look at an overview of what going on um we can see here how proteins are made in the rer right and these here are transport vesicles you know can i write that does it like it if i write on the animation hey i can okay so the transport vesicles actually um but off from the er carrying those proteins and you can see it fusing with the golgi body and in the golgi body it's being modified so it becomes red here again it's just a diagram and it's packaged into secretory vesicles to be kind of uh transported out of the cell and this is a process of exocytosis so i hope you can imagine this flow uh let's look at uh another image of this right this is a label image uh you can see here again the proteins form in the rough endoplasmic reticulum then my proteins form as in polypeptides form amino acids are not formed right amino acids are kind of joined together to make proteins anyways proteins are synthesized in the rer transport vesicle from the ar goes to golgi apparatus goes with secretory vesicles and that security vesicle basically fuses with the plasma membrane in a process called exocytosis you can see here and it fuses and the protein gets released out of the cell this is such a cool animation here because it really shows how the microbots basically the phospholipid bilayer is able to fuse and uh basically this vesicle can become part of the cell surface membrane i usually get a question miss if there's a lot of exocytosis will it make the cell bigger because the cell surface membrane kind of adds right it adds to the cell surface membrane and the answer is very possibly yes but don't forget the same cell may also do the reverse process which is endocytosis and if that's the case then the cell may not grow as much you know also the vesicle is very tiny compared to the size of the cell so you know like that difference of expansion might not be very big anyways moving on how do we actually put this in words right so this is the list of the cell structures involved how do we talk about it number one there are synthesis of protein in the ribosome or the rdr the transport physical butts off the right endoplasmic reticulum and fuses with the golgi body there's modification of protein in the emoji body and separation of secretory physical from negotiate body can occur after that and the vesicle can then travel to the cell surface membrane where it fuses and this contents of the vesicle can then be secreted by exocytosis now bear in mind that this process also works to embed a protein at the cell surface membrane the only difference between a protein and the cell surface membrane and a secreted protein would be that in the vesicle instead of the proteins being inside this is a secreted protein the protein would be on the surface of the vesicle so when the physical when the secretory vesicle fuses with the cell surface brain the vesicle membrane also becomes part of the cell surface membrane right so that process this cell surface membrane then becomes part sorry this cell surface membrane protein then becomes part of the cells against membrane just by being at the phospholipid bilayer of the physical instead of the inside [Music] that is the production and secretion of proteins let me give you a little exercise this is a past year question and it says when a mucus is secreted from a goblet cell and trachea this event take place this this and this what is the sequence in which these events take place pause the video think about it and talk about it okay by the way mucus is made up of new sin and mucin is a glycoprotein which is a combination a protein that is made out of carbohydrate therefore glyco and a protein so that should give you a hint on how to answer this question pause the video you're done okay so what is the sequence in which this events take place the answer is for sorry one four two three so addition of carbohydrate protein which happens at the goal g or possibility er doesn't matter number two after it's modified it undergoes your er the separation of the vesicle from the goji paradise right this would be a secretory vesicle number two there's fusion of the secretory vesicle with the plasma membrane and therefore secretion of the glycoprotein which is mucin out of the cell to a process called exocytosis and that is the process of excreting excreting no secreting my excluding secreting protein from the cells three more cell structures ago before this video ends don't forget that golgi in addition to you know making secretory vesicles also is in charge of synthesizing lysosomes which is actually a vesicle as well but it's a special vesicle with um hydrolytic enzymes or lysosome signs and the function of these enzymes are to break down unwanted structures via hydrolysis in an acidic environment this vesicle has an acidic environment to kind of facilitate that process now unwanted structures is allowed worn out organelles is okay or dead cells is fine but the exam would reject reject that means they were minus marks if you wrote dead organelles because organelles are not living things we don't see organelles as living we see whole cells as living so do not write dead organelles right worn out or damaged organelles would be fighting so this is definitely not what they want right worn out organelles unwanted structures or dead cells are accepted now in white blood cells especially they have plenty of lysosomes and these lysosomes are able to digest bacteria and you can see a picture of a white blood cell here you can see how the bacteria is engulfed by this cell and then the lysosome and the phagosome actually fuses and and this exposes the bacteria to the lysozyme and the lysozyme breaks it down and then like the debris cell debris actually gets thrown out the cell via exocytosis now this process you will learn in more detail in the coming chapters i know i say that a lot but i really do explain them in more detail later on anyways two more cell structures to go number eight mitochondria now we all know mitochondria is the powerhouse to sell but if you're writing an examine cambridge you'll get it wrong now what should you write instead now mitochondria synthesizes atp in the form energy in a form of atp okay it's not here yet let's look at some of the other details first now it is a relatively large organelle it's not as large as the nucleus uh i think if you put them in order nucleus is largest followed by the chloroplast followed by the mitochondria so mitochondria mitochondria has double membranes as well actually the nucleus corpus and mitochondria are friends they all have double membranes mitochondrial in particular has a special thing inside it's called cristae not to confuse with cisternae for goji and er this is cristae which is folded in a membrane inside the mitochondria and this increases surface area for a lot of protein and basically energy atp synthesizing equipment the interior solution is called the matrix and it actually contains a lot of enzymes and also 70s ribosomes which we discussed earlier and also small circular dna and like huh small circular dna okay so it's still double helix dna but instead of like you know a huge like a linear strand it kind of joins back on itself so it's a still double helix but this is a bad representation drawing but it kind of loops back on itself this would be circular dna this is linear now this small circle dna would code for some mitochondria proteins that are needed for their for energy synthesis yeah okay mitochondria also divides by minor efficient which is quite cute so it kind of cleaves our middle and it separates it to become two here and other reason for that weirdness in general is that mitochondria are hypothesized to have a prokaotic origin does that mean this means that maybe once upon a time mitochondria as well as chloroplasts that you will see later actually were other living cells maybe other living bacteria which were able to synthesize their own energy in the form of atp chloroplasts as well may have been a bacteria in the past that could harvest sunlight and convert it into energy and food and basically our ancestral cell long time ago were able to use these uh other bacteria in order to make energy in the form of atp for itself or harvest light to form food like plants too so yeah that's why it's kind of interesting that it has its own dna it's his own ribosomes and it has double membranes these are all some form of evidence that this bacterial hypothesis is true it's kind of interesting so mitochondria again not power half the cells yes it's positive but you can't write it that way so how do you write it the function is the site of aerobic respiration it's is to synthesize atp or produce energy in the form of atp the reason why i keep saying atp instead of just synthesizing energy is because they reject as in their minus marks if you write produce energy alone without mentioning atp because energy can't be created or destroyed right physics so mitochondria don't produce energy it just produces energy in a form of atp which would be able to be used easily by different reactions of our cell yeah now aerobic respiration what does this term mean now when we say respiration we often think of breathing in and breathing out there's not respiration we're talking about we're talking about the conversion of glucose oxygen into carbon dioxide water and atp that is what we mean by aerobic respiration breaking down food in order to form energy in the form of atp again please do not write these two sentences right here let's look at this electron micrograph again this is because we need to do three things right and treating this name it recognize it and know its function and also in in a certain extent because an x and know its function and structure as well so what are the things you see here that you could identify what is a is being able to see now a is the biggest organelle which is the nucleus this is a very zoom in diagram we know the nucleus because we see like these chromatin-like structures hanging about and it's really big it's not an other cell this this is inside a cell now this here is mitochondria b is mitochondria in a mitochondria you can see here we have some inner membranes going on this are cristae and yeah they are pretty large too in comparison not as it's not as big as the nucleus but it's still pretty large okay it's too pretty large now how about c now c is a little bit distant from the nucleus right so it's not maybe not very continuous but it does have kind of a rougher appearance uh so i would like like this this is rough and this is kind of near so this is probably the rough endoplasmic reticulum and i would say that this would be the rough endoplasmic reticulum as well it's just maybe continuous because it's a similar thickness you'll see but honestly if you're not showing an exam you can easily write endoplasmic reticulum in general if you're not sure if it's suff or rough and if it's really far away then you might goji um usually they will only ask you what is obvious not what is debatable yeah so that's the mitochondria this is also the mitochondria this is also the mitochondria get used to the diagrams man you can see the inner christie looks beautiful sometimes it looks cylindrical not cylindrical like rod shape that's what we call this shape by the way rod shape um and sometimes it looks circular so oval circular what's up now it's because you're probably seeing it differently one is a longitudinal cross-section when it's like a transverse section also shape of mitochondria may vary and maybe like you're viewing it from different angles or maybe um it's just divided all right it's just divided by binary efficient so you can't really tell the shape properly like the shape does not fix so yeah it's mitochondria and this is actually a common question in past years moving on to our last organelle forages video chloroplasts we saw some pictures of chloroplasts before but here is a little representative diagram it is also a relatively large organelle second in place after the nucleus it's definitely visible under the light microscope it is oval shaped uh it is two membranes it has chlorophyll it has thylakoid um these thylakoids are flattened membrane stacks and multiple thylakoid stacked together is called grana and this grana is in a liquid of uh coal in a liquid inside called stroma not inferior solution interior solution i was reading it around on my brain anyways grana stroma right grana again is tyler called sex stroma is the fluid now just like mitochondria it's special right again it's two membranes it contains some of the ash ribosomes small circular dna and because chloroplasts harvest light energy to make food um they also have starch grains inside chloroplasts it also divides by binary friction and all of this is because well we probably it probably has a prokaryotic origin this is chloroplasts in real electron micrograph diagrams you can see the grana here the thylakoid stacks it looks beautiful don't you think haha now under light microscope we can definitely see this as well and they will appear green because of the chlorophyll now here is a plant cell and you can see the kind of contrast in size between everything else you can see the nucleus which is the biggest organelle usually now the vacuole is full of water at this point so it looks a little bit bigger nucleus quite common in plant cells but not all but vacuoles are not usually visible under like the light microscope so nucleus is still the most visible largest organelle plants anyways uh you can see that next up like the next biggest state would be the chloroplast and they are huge don't you think in comparison with everything else and we can see the mitochondria here being slightly smaller from the pure plus and the endoplasmic reticulum isn't even very seen the golgi apparatus is barely visible uh there and that's because this image is probably not high resolution enough and doesn't have enough of a magnification to visualize those fine membranes but yeah look how big chloroplasts are right okay let's talk about the function a little bit now the function obviously is the site of photosynthesis now this may come as a surprise because there are two main processes in photosynthesis the light dependent reaction and this is where like energies absorb and water is used to synthesize atp so surprise surprise mitochondria is not the only powerhouse of the cell especially in plants planets because the chloroplast is able to synthesize atp as well but this atp is used inside the chloroplast to convert carbon dioxide into glucose in that light independent reaction the carbon dioxide the conversion of carbon dioxide into glucose is called carbon fixation and uh you don't need to think about this right now this term is like dependent like independent you just need to know that it's synthesizes atp so photosynthesis and what it does is to convert carbohydrate glucose so only the red and blue words here however you will learn these processes in more detail in a chapter 13 specific way yes chapter 13. so yes that is the car class and i think we are done with nine different structures long video lots of content i hope that was helpful though um all the essential information are in red and bold just in case you don't know uh and these are all based on maps games if you like a copy of my notes they will be available online look at the video description for more information see you next time bye