Understanding the Endoplasmic Reticulum: Structure and Functions Explained

foreign what's up Ninja nerds in this video today we're going to be talking about

the endoplasmic reticulum we'll go over the structure and the function of it all right so first thing before we get

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to go check that out all right let's start talking about the endoplasmic reticulum and there's two types so we

have to basically go over their structure which thank goodness it's not too bad their functions a lot more

involved though but there's two types one is the rough endoplasmic reticulum the rough endoplasmic reticulum okay and

I'm going to write rough endoplasmic reticulum right if you guys need it it's right there but the rough endoplasmic

reticulum the big thing to know is that this is a again a tubular structure that is continuous with the outer

membrane of the nuclear envelope but the big difference here is that again there's another structure here this one

here in this kind of like maroonish color is called the smooth ER or endoplasmic reticulum it's also a

tubular structure that's continuous with the outer membrane of the nuclear envelope

and they're both having their membranes made up of phospholipid bilayers the big difference between the two is you see

these red dots that are kind of like studded on the outside of the rough ER that's why we call it rough it has many

ribosomes on its surface this one has no ribosomes on its surface that is the big

difference and that's it let's not make it too complicated for the structure of the endoplasmic reticulum it's a

membranous tubular structure made up of a phospholipid bilayer that is continuous on the outer membrane of the

nuclear envelope rough ER started with ribosomes smooth ER no ribosomes studied on the surface after ribosomes leave the

nucleus they will have the important job of synthesizing or making proteins outside the nucleus the ribosomes and

the rest of the organelles float around in cytoplasm which is the jelly-like substance

ribosomes May wander freely within the cytoplasm or attach to the endoplasmic reticulum

sometimes abbreviated as ER there are two types of er rough ER has ribosomes attached to it and smooth ER

doesn't have ribosomes attached to it the endoplasmic reticulum is a membrane-enclosed passageway for

transporting materials such as the proteins synthesized by ribosomes proteins and other materials emerge from

the endoplasmic reticulum in small vesicles [Music]

where the Golgi apparatus sometimes called the Golgi body receives them let's now dig right into the functions

right let's not waste any time endoplasmic reticulum functions particularly pertaining to the rough ER

so we're going to talk about that one first the one that started with ribosomes what is his job

really the big thing is that all the time when you're in school you get stuck with having to memorize these like lines

oh it's involved in approaching synthesis and modification and sending no no don't memorize understand

so first thing here as we have here the nuclear the nucleus if you will inside the nucleus you have

the DNA now DNA is really cool in the sense that what it can do is it can make something called RNA via a process

called transcription so here the particular one that we care about is called mRNA and no RNA is basically

carrying the code that whenever it goes ahead and leaves the nucleus via the nuclear

pores it goes and it binds onto these ribosomes that are studded on the surface of the rough ER here's again

another mRNA and they're going to bind onto this the ribosomes in combination with TRNA

and rrna will help to be able to translate the MRNA and make a very special structure

it's going to synthesize proteins and what we're just going to do is we're going to show a couple of them

here so here what it's going to do is the MRNA will be translated by the ribosome the MRNA it'll be translated by

the ribosomes and make proteins here's my proteins this protein once it's pushed into the

Lumen of the endoplasmic reticulum it then has to go in this March through

the endoplasmic reticulum and along the way it undergoes modification so this protein is not fit to be excreted yet we

got to modify it a little bit and tag it so you know we do here's the protein right here's the

protein here's this enzyme this enzyme is going to do something very interesting where in one hand it's

going to have the protein it's going to bind onto the protein but it binds onto a very specific amino acid on the

protein so here's the specific amino acid on the other end it's going to have

something called oligosaccharides which is basically sugar molecules and what it's going to do is it's going

to find a very specific amino acid on that protein called asparagine

asparagine it's a very specific one and then what it's going to do is it's going to take this sugar we call this

oligo that's a heck of a name saccharide so I just like to put sugar it's going to take this and add that on to the

asparaging of the protein so let's say that here is the asparagine right here

what's going to be linked onto this oligosaccharide molecule this was the protein non-modified this

is the protein modified you know what they call this and this is why I'm kind of focusing on it because there's a

specific name to it my friends this is called in linked

glycosylation glycosylation this is one of the primary ways that the rough ER modifies son of a gun glycosylation

modifies specific types of proteins now if you think about it you're taking a protein and adding a

sugar residue onto it you know what you're really making it like glycoprotein and glycoproteins are

really interesting in the sense that when we make glycoproteins there really only is a couple destinations that are

primed for glycoproteins so now what I'm going to do is I have this

glycoprotein that I've kind of helped to synthesize and modify a little bit so here I'm going to draw some

oligosaccharides that are coming off it there's my glycoprotein I'm going to butt it off of the rough

endoplasmic reticulum into like a little vesicle if you will all right so here's this vesicle that comes off of the rough

endoplasmic reticulum and inside of it it's going to have my protein and then connect it to it it's going to

have this sugar residue so there's my glycoprotein what happens is

this vesicle needs to know where am I going so you know how it knows where it's

going proteins kind of get stuck onto this Edge

they kind of get stuck onto this edge here of the vesicle and what it does is it

tags this vesicle and says hey you have to go to the Golgi apparatus you know what this protein is called

it's called cop2 this is called cop two protein and this cop2 protein is

basically a tag that says you need to go from the rough endoplasmic reticulum to the Golgi apparatus and then from here

it moves nicely towards the Golgi this is your Golgi and there's two ends the CIS end which is coming from the rafiar

and the trans-in which is leaving and going to the membrane right from here this will fuse

with this structure here it'll fuse beautifully with the Golgi apparatus and then what it'll do is it'll say here

you go Golgi here's this protein that I synthesized and I modified a little bit by doing

in-link glycosylation you do any more modifications Booboo do what you need to do

but then after that I want you to package him and I want you to send him to three locations that you feel

appropriate so we're not going to go through the mechanisms of the Golgi right now we'll cover that in the Golgi

video but he'll modify it a little bit more and then after he modifies it

he then says all right the rough ER tagged a specific type of

faster call to send to me now from here I can send this vesicle to three locations

and this is very very important all right what are these locations that I'm going

to send this glycoprotein to one of them is I can send it to the cell membrane to be incorporated into the cell membrane

right so now what I can do is I can take this vesicle here and I can have it Go fuse with the cell

membrane and if it fuses with the cell membrane maybe this will become some type of channel protein or Carrier

protein some type of protein here that is incorporated into the cell membrane that's one thing

this could be a lot of different things we already talked about what membrane proteins do this is a glycoprotein that

maybe is involved in carrying maybe some type of Channel maybe it's a peripheral protein that acts as an enzyme maybe it

links different things together it's a membrane protein that's one so one thing I can do is as I can send

this to the membrane second thing I can do is I can actually cause this to go to the cell membrane

and actually be fused with the cell membrane but in this case I'm going to excrete

this particular protein so now what I'm going to do is I'm going to release this protein out into the wild to be free

and this glycoprotein maybe it's a hormone maybe it's a neurotransmitter but this is a secretory protein so one

thing I could do is I could do membrane protein membrane protein is what it will become

second thing is it'll become a secretory protein maybe this will become like a hormone of

some type and the third thing the third thing is it becomes

specialized the third thing is to become specialized and becomes this special vesicle

that really is a nasty nasty organelle and it can actually become very helpful in breaking down other different things

inside of the cell you know what these nasty little enzymes can be called

this could be a part of lysosomes this could be a part of lysosome so the third thing it could become is

lysosomal protein so lyso zones it can be incorporated into lysosomes

this is the job of the rough endoplasmic reticulum so when you get a hint of it it is heavily involved in the synthesis

of the proteins push into Lumen modified via inland glycosylation makes vesicles and tags them to send

them to the Golgi Golgi does some more modifications and then says okay rough ER told me to do three things with this

incorporate into the cell membrane secret it or turn it into lysosomal proteins that's it nothing crazy to it

so now instead of memorizing words we understand this but the next step that we have to take here is if we say that

it's this organelle if you will is involved in protein synthesis then we should know

what type of cells in the body if you were asked this on a test are rich in rough ER because they synthesize lots of

proteins this would be the pancreas the pancreas is a huge one so we call this the

exocrine portion of the pancreas so the pancreas particularly the exocrine portion because these men whoo they'd be

pumping out those pancreatic digestive enzymes so many digestive enzymes that need to be released to break down all

the food that we eat these ones plasma cells you know what plasma cells are responsible for these

things pump out antibodies antibodies are glycoproteins my friends so because they need to make tons and tons of

antibodies these should have a very heavy type of rough ER another one is called goblet cells you

find these a lot in like your tracheal lining your stomach lining and they produce massive amounts of mucin which

is a type of protein and that is another one lots and lots of mucine proteins to coat the lining of the cells

and the last one is neurons neurons are a big one and we actually give this specific ER that's found in the Soma or

the cell body of the neuron a very specific name we called a nissl body the missile body all it is you take

what's called initial stain so basically the rough ER right it has like this charge to it so what you do is you give

them a particular die and the die will kind of bind with the proteins of the rough ER and give it like this kind of

stained color and that's what we call the nissl body but basically neurons they need to have lots of these because

they need to make tons and tons of neurotransmitters right

so that's the big concept that I need you guys to understand so we know that rough ER is involved heavily in the

synthesis of proteins the modification of proteins the packaging of them to send them to the Golgi and then from

there they are destined for three particular end points that's the big thing to take away and then which cells

are rich in them the ones that make lots of proteins all right now let's talk about the smooth ER all right my friends

smooth endoplasmic reticulum the functions what does it do really the big thing that I want you to remember okay

we talked about how the rough ER is a site of protein synthesis modification of proteins package and sends them to

the Golgi from the gold you can become membrane excretory or lysosomal we talked about that what I want you to

remember for smooth ER is it's really the site of lipid synthesis so what do you mean here okay watch this

you know uh we can make a couple different types of lipids and really it all starts with this very special

molecule that we have within ourselves called acetyl COA you guys probably remember that right we take like

something like glucose and we can convert this into acetyl COA certain amino acid can become acetyl COA a lot

of different things will actually convert into acetyl-coa but acetyl we know we can actually go into the Krebs

cycle and help to generate ATP right you know what else it can do I can get taken up

into the smooth endoplasmic reticulum and within the smooth endoplasmic reticulum what happens is the acetyl COA

can go through various different types of reactions which are carried out by multiple multiple enzymes but I'm not

going to go through here I'm just going to give you that acetyl COA it can go through many different enzymatic steps

and what can happen is is we can take acetyl-coa and start linking these two carbon chains together and then what you

can make out of this is maybe you make a fatty acid right so maybe from this one of the things that you make is a fatty

acids and usually the enzymes that are really heavily involved in this particular process here if you really

wanted to remember it it could be done via what's called fatty acid synthase right that's one thing that we could do

the second thing is we can do is we can take a seat up we can take these fatty acids that you make from acetyl-coa and

combine them with phospholipids so I can add on like a phosphate group on to that I can add

like a residue like something like choline and make phospholipids so I can also synthesize

phospholipids now the question that you probably have from this is okay what would I do so I know it's synthesizing

fatty acids I know it's synthesizing phospholipids what can we do with those fatty acids

you can do a lot of things with fatty acids with fatty acids I could I could make things like triglycerides

I could do things like utilizer for ATP production right so I could break down fatty acids via beta oxidation to make

ATP I could combine them with glycerol and make triglycerides I can do a lot of different things with this you know what

else I could do with it I could make phospholipids you know phospholipids could actually become phospholipids are

great for being a part of what your cell membrane we already talked about this so many different things it's really

helpful that phospholipid bilayer you know what else we could do we could take the acetyl-coa through

multiple multiple steps we can make this big kind of like ring structure here that you could have it's super cool this

thing could be cholesterol so what else could we synthesize we could synthesize cholesterol

now cholesterol is really really cool because cholesterol we already know can do so many things it can be incorporated

into your cell membrane you can use it to make bile acids which is helpful for being able to emulsify

fat you could use it to make lipoproteins and you know what else you could use it

for which is really really high yield for your exams you could use it to make sex hormones

or other types of steroid hormones so that's a really really important thing to be able to take away from this

and all of this is carried out by these cute little enzymes that are located within

the smooth endoplasmic reticulum they help to be able to take all of these things like acetyl-coa convert into all

these other intermediates and substrates and then form fatty acids phospholipids or cholesterol

fatty acids can be utilized for ATP via beta oxidation they can be used to make triglycerides of a combined with

glycerol you can make phospholipids if you add a phosphate group and other types of residuals onto them which can

be incorporated into the cell membrane and you can make cholesterol which can help to make cell membrane components

fluidity it can also be involved in bile acids lipoproteins steroid and sex hormones let's actually dive into that a

little bit so if you think about cholesterol real quickly

when you know that it helps to be able to make things like sex hormones if you think about this in the testes the

testes would have a very very rich smooth endoplasmic reticulum right so the testes in the ovaries have to have a

very rich smoothenoplasmic reticulum just like the rough endoplasmic reticulum is rich in

what the pancreatic exocrine cells it's rich in the plasma cells it's rich in the goblet cells or in the neurons and

the same thing testes what do they make testosterone so actually take the cholesterol and conform it to make a

very special hormone testosterone ovaries to make things like estrogen they'll make things like progesterone

so that's another thing all of these things are derived from cholesterol so from here you can actually take

cholesterol and modify it a little bit more and when you modify it you can make these sex hormones same concept exists

we have adrenal gland and on the outer parts of the adrenal glandia the adrenal cortex they're also super rich in the

smooth endoplasmic reticulum they'll take all the acetyl-coa make a bunch of cholesterol modify the

cholesterol and make steroid hormones some of these they can make is what's called cortisol

this is made by something called the Zona fasciculata then they can make another one called

aldosterone this is made by the Zona glomerulosa which is a part of the adrenal cortex

and they can also make other types of random gonadocorticoids which we can call a dehydroxy epion dostron and

epiongosterone these are gonadocorticoids but you see how they again smoothen the plasma curriculum

makes cholesterol and then they use enzymes to modify that cholesterol to make steroid hormones or modify to make

sex hormones in the same way we talked about steroid and sex hormones but we can also use

these hepatocytes hepatocytes are also really cool because they have a lot of smooth endoplasmic reticulum in them

and the reason why is they can take this cholesterol that they synthesize and modify it to make two particular things

they can modify to make something called bile acids which are really important for being able to help emulsify big fat

globules and they can also make things like lipo proteins things like LDL things like

vldl things like HDL all of these things are helpful in that structure so that's really really important when

we think about what the actual smooth ER does for lipid synthesis it helps making fatty acids phospholipids cholesterol

and then in certain cells you can take that cholesterol and again cells that are rich and smooth endoplasmic

reticulum and make hormones such as sex hormones and intestines in the ovaries testosterone estrogen progesterone

corticosteroids or mineral corticoids present in the adrenal cortex you can take the cholesterol mixed steroid

hormones or you can make bile acids and lipoproteins in the hepatocytes so really really important there

all right what else does the smooth ER do a lot of other things but the big thing that we've covered so far is lipid

synthesis fatty acids phospholipids cholesterol from the cholesterol steroid hormone sex hormones bylasses

lipoproteins the other thing that's really really important for is in hepatocyte so this

is our liver all right this is our liver and the liver it's involved in what's called biotransformation This is

basically drug and toxin metabolism that's the fancy word for it so here we have hepatocytes these are our

hepatocytes and these are parasites we already know are rich and smooth ER for what lipoproteins bile acids but you

know what else it's rich in smoothie R for another particular thing called biotransformation so what I want to do

is I want to zoom in on these hepatocytes and take a look here's my smooth endoplasmic reticulum

in the smooth endoplasmic reticulum there is a special enzyme this is called the cyp450 the cytochrome p450 system

what happens is let's say that we come in contact with a drug or a toxin

or alcohol when these things get taken up into the hepatocyte

they all can be brought into the Smoothie are when they're brought into the smooth

endoplasmic reticulum they interact with the cytochrome p450 system and the basic thing that happens out of

this is that the cytochrome p450 system will take and metabolize these drugs toxins or alcohol by adding on different

types of groups onto them maybe adding hydroxyl groups onto them maybe adding like these like these groups onto them

that make them super super water soluble so basically it takes a drug takes a toxin takes alcohol metabolizes them

into particular substances that maybe are very water soluble

and you know what that's really important because water soluble substances are

easy to be able to excrete into the Poo that way and water-soluble substances are easy to

excrete into the urine so it makes it easy because now the smooth endoplasmic reticulum will

metabolize the drugs the alcohol the toxins making them water soluble will enhance the ease of excretion

of these drugs Isn't that cool so a parasites are really rich and what smooth ER for what type of function one

is lipid synthesis for cholesterol because they're able to make steroid I'm sorry bile acids and also lipoproteins

they're involved in the sex organs the adrenal cortex fatty acid synthesis phospholipid

synthesis they also play a role in biotransformation biotransformation is again what taking drugs toxins alcohol

neutralizing and metabolizing them making them water soluble easy to be excreted okay so we got bio

transformation and lipid synthesis for the smooth ER what else does it do another really cool function here

is it plays a role in glucose release so again here's the hepatocytes here's your liver right

and then these hepatocytes again we're kind of noticing a trend here that the liver cells are super rich and smooth

they are so are they test these ovaries in the adrenal cortex but hepatocytes have been kind of an overarching theme

that we've noticed within the hepatocytes we know that they're rich and smooth they are

obviously at this point but here's another cool thing the liver does a process called

gluconeogenesis and basically this is where the liver will synthesize glucose from non-carbohydrate sources

things like lactate things like amino acids things like odd chain fatty acids things to that effect now here's what's

really important when glucose gets brought into the cell when glucose is brought into the cell in

some particular way right usually through a reaction it'll undergo this process where it gets converted

into what's called glucose 6-phosphate right and that's via a glucokinase or a hexokinase process so we add on a

phosphate you know the problem with this is glucose 6-phosphate can't exit the cell

it can't leave the cell so because of that it is stuck in the cell so if I want to get this glucose out of

the cell I have to go back this way the only way glucose can leave is in this fashion it can come in as glucose and it

can leave as glucose it cannot leave as this well how in the heck do I get this

glucose 6-phosphate to go back into glucose the only way is we take this glucose

6-phosphate when we pump it into the smooth endoplasmic reticulum and then

the glucose 6-phosphate will get reacted with these enzymes called glucose 6 phosphatases and what they will do is is

they will rip off that phosphate and convert it into glucose so that we can pump the glucose

out of the hepatocyte so that is the concept that I want you to understand is that in the actual

smooth ER there's this special enzyme and this enzyme is a phosphatase phospha

tase and what it'll do is it'll cut this phosphate off of the six carbon of glucose liberate glucose so that it can

now be released out of the cell that's one of the jobs of the smooth ER Isn't that cool so we got lipid synthesis

we've got biotransformation which is a fancy thing for drug alcohol toxin metabolism of neutralization to be

excreted and glucose really specifically cutting off of the phosphate of the six carbon of glucose so it can be liberated

and that's only at the smooth ER the last function I want to talk about is calcium storage let's talk about that

all right so smooth ER at this point we've covered lipid synthesis biotransformation we've overcome also

glucose release the last thing is calcium storage and release now it's very interesting because

calcium is a really interesting thing that in specific type of cells so muscle cells so skeletal muscle cells cardiac

muscle cells smooth muscle cells they have a very specific like modified smooth ER so I really want to I want you

to think about this is called a modified smooth endoplasmic reticulum and you know what we actually call it because we

don't like to call it that we call it the Sarco plasmic

reticulum because it's very very close to the cell membrane of the muscle cell and what's cool about this is that let's

say here is the sarcoplasm this is the basically uh the I'm sorry the sarcolemma this is the muscle cell

membrane right whenever we have like a neuron let's say and this neuron

stimulates because it releases acetylcholine it depolarizes the cell membrane

that depolarization will then travel it'll make this entire cell membrane positive there's like a little

invagination in skeletal muscles it's called the T tubules and what happens is this positive charge

moves down the cell membrane it activates the sarcoplasmic reticulum which is a modified smoothie r

and inside of this sarcoplasmic reticulum is rich in calcium and if I stimulate this smooth ER I'm

going to open up channels that are kind of storing calcium inside of it to release it and then what calcium will do

is calcium is a very important structure that helps to activate

our myofilaments and so what it'll do is it'll bind onto very specific molecules that are present on the myofilaments and

stimulate them to initiate the contraction process so that's another cool thing so we know

now that the smooth ER is involved in lipid synthesis we know that it's also involved in biotransformation we know

that it's involved in glucose release and we know now that there is a modified smooth ER in muscle cells that contains

Calcium and when stimulated when it's depolarized from again being stimulated by a nerve or whatever it may be it'll

release calcium into the cytoplasm to allow for this muscle cells the myofilaments to contract we don't want

calcium just sitting out here in the cytoplasm all the time so it stores it so when it's needed it can then be

released and then guess what when you're done with contraction you go to relaxation guess where the calcium has

to go back into the sarcoplasmic reticulum to be stored for the next contraction to be pushed back out

all right my friends in this video we cover the endoplasmic reticulum the structure and the function I hope it

made sense I hope that you guys enjoyed it and as always until next time [Music]

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