Comprehensive Guide to Eukaryotic Cell Structure and Organelles

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