Understanding Lysosomes: Structure and Function Explained

foreign ERS in this video today we're going to be talking about the lysosomes we're

going to talk about their structure and we'll also talk about their function before we get started if this video

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can go check that out all right but without further Ado let's talk about the structure and function of lysosomes so

nothing crazy here we talk about lysosomes one of the things I want to do is recap a little bit of things that we

talked about with the rough ER things that we talked about with the Golgi things that we talked about with the

cell membrane so it's going to be somewhat of a recap but it's okay that's good that's what helps you guys

repetition understand these things so when we talk about lysosomes what I want to know is their structure but how are

they made all right these are really interesting so when we actually talk about lysosomes it all starts at the

nucleus believe it or not so in the nucleus you guys know that we have chromatin and one of the components of

Chromatin is DNA if we were to take DNA and read it and make a single stranded structure called an mRNA that would be

called transcription so from this DNA molecule we're going to make something called mRNA and this is via the process

of transcription of the DNA then the MRNA will then go and bind with a ribosome and what we

know is that ribosomes can exist in various forms they can exist in this cytosolic form in other words just a

free form which floats in the cytosol usually that one is to make proteins and enzymes that are functioning in the

cytosol that go to the mitochondria but the other ones are membrane bound to the rough endoplasmic reticulum these are

making proteins that are designed to go to three particular locations the cell membrane to be excreted or to become

lysosomal proteins you're getting a point here right so once we take this mRNA we bind it with the rough ER

ribosomes the rough ER ribosomes once they fuse here they start to synthesize a particular protein so to be a protein

synthesis that'll occur here in the actual ribosomes now once that occurs here's my protein that got synthesized

in the ribosome then what it's going to do is it's going to start making its way through the rough ER where it'll have

some further modifications you guys remember what we said her curves here the in-linked glycosylation will add a

sugar residue to asparagine one of the amino acids on this protein then what we'll do is

once we've modified this protein so let's say here we modified a little bit here's the Core protein and then all we

did to this Core protein is we added a little you know sugar molecule there then what we do is we're going to

package it into a vesicle out of the rough ER and say Hey you now need to go to the Golgi because the golgi's got to

modify you a little bit more to make you very very specialized and determine where you're going to go

so then we make a little vesicle and then how do we get that vesicle to go to the Golgi you guys remember what was

that pink protein that we put on its surface that helps it to guide it towards going to the Golgi what was that

protein called this was the Cop 2 protein all right just looks you know checking your understanding

once this vesicle fuses with the Golgi membrane it then releases the protein contents here this modified protein at

this point into the Golgi apparatus and and then in the Golgi apparatus it'll be further modified

and when it's modified then what will happen is it'll then get packaged into vesicles in the Golgi that'll be sent to

three particular locations out of these let's say here is the three particular locations here's the protein

the proteins the proteins are all synthesized here some of the proteins can get packaged

into these vesicles here right and then from this this can go to three particular locations

one of them is they could be excreted from the cell so these could be an excretory protein we know this already

right so this is pretty obvious that this thing could be excreted so here's my excretory protein the other

aspect of this is that that Protein that's been modified in particular ways can also be

incorporated into the cell membrane so here's my protein that's now been incorporated into the cell membrane and

again all of these have these like particular sugar residues on them the last thing is they could become

lysosomes here's where we have to add another quick fact in we talked about in the Golgi that

there's three modification mechanisms right and the rough ER there was one it was in-link glycosylation

and the Golgi there was trimming of the inline glycosylation there's o-link glycosylation so we added sugar residue

onto the oxygen of serine and threonine or there was phosphorylation this is the key one that I really want you to

remember there's a sugar that's present on on the sugar residue there's a molecule called mannose when we

phosphorylate mannose so we call this phosphorylation I'm going to write this down because this is a crucial step here

so we actually do phosphorylation of what's called mannose which is basically one of the sugars

that are present on that long sugar residue that was attached we put a phosphate on it once you do that you

then say these proteins these glycoproteins are now destined to go and become a lysosome that is the thing that

I want you to remember okay so we talk about lysosomes lysosomes are really just these spherical vesicles that have

a membrane that was formed an actual phospholip bilayer that was formed by the Golgi and they contain glycoproteins

that were synthesized from DNA going to RNA going in to make proteins modified in the rough ER and then modified in the

Golgi in what particular way what was that big big modification thing that I told you this is super crucial here is

phosphorylation of mannose that's a big thing and then it determines it going to make a lysosomes

so now we have our lysosomes now the cool thing about these lysosomes is we have to talk a little bit about

these proteins these glycoproteins these glycoproteins that are all located in these vesicles are very very specific

let's come down and talk about them so here we have a lysosome I'm just cutting the

lysosome so we can take a look inside of it all of these are going to be your lysosomal

proteins we also like to call these special types of enzymes you know they're really nasty

little enzymes we call them hydro lytic enzymes they have the ability to cut big macromolecules and that's really

really important for their function so if we were to take some of these actual hydrolytic enzymes what could they break

down one of them is actually called a nucleases oh that's

pretty obvious what this sucker could do then right if this is a nuclease it has the ability to break down what so this

can break down RNA and DNA that's a really really important thing especially if there's some type of like pathogen

like a bacteria that has RNA and DNA and I want to break that down I can do that or other things another one

is proteases proteases our big one we have the ability to break down proteins so we can break down proteins we can use

nucleases to break down RNA and DNA what else we got in this sucker here we also have lipases

lipases they can break down lipids they can break down lipids and we know that multiple different things have

lipid membranes bacteria can have lipid membranes our own cells can have lipid membranes what else

another one is called glucosidases so glucosidases you obviously can tell that these are going to be breaking down

carbohydrates glucosidases these will break down carbohydrates

okay we'll break down carbohydrates and the last one here is an interesting one we call these acid phosphatases we

will mention them briefly a little bit later but I just wanted to write these ones down these are called acid

phosphatases these are really really special to only breaking down bone tissue so

these are actually released by special cells called osteoclasts that contain lysosomes and these will break down bone

tissue which has a lot of different things within it but these are the biggest particular enzymes that are

contained within lysosomes so as you can see they can break down almost every macromolecule possible and then even a

little extra but the question is is why would they break these things down

in what particular way would they break these things down we'll talk about that in a second but another cool thing is

that these enzymes they function at a very particular pH we know that most proteins and enzymes at certain

temperatures you can denature them as certain pH as you can denature them well these actually prefer to be at lower PHS

so because these enzymes depend upon a lower pH there's a special you know Channel or protein pump that's present

on the lysosomal membrane you know what this is let's actually zoom in on it right here so I'm going to zoom in on

this particular protein right here this is called a proton atpase which means that it depends upon protons so let's

say here's the inside of the lysosome and here's the outside of the lysosome I want protons to be pumped

into the actual lysosome because if it does that it lowers the pH I want the pH to be approximately around five you want

to know why because at this pH it stimulates or keeps these enzymes activated

and that is a really important Concept in order for these enzymes to work we need their optimal pH to be around this

point so I keep these channels Super Active and using ATP in order for me to pump these protons into the cell to

maintain the optimal pH for these puppies to function so in order for me to do that what do I need I need to

utilize a lot of ATP to be able to perform the action of these pumps that's a really important

concept so we have an idea now that lysosomes are made of glycoproteins particularly what types of proteins

hydrolytic enzymes that can break down every macromolecule possible they're actually made

from the transcription of DNA to mRNA to make proteins in the rough ER they're modified they're packaged sent to the

Golgi modified in a particular way this way to make lysosomes they have a phospholipid bilayer that's from the

Golgi and the proteins that were synthesized accordingly now the question is is

what would we use all of these enzymes to break down and what type of physiological functions let's talk about

that we now know that we have to break down some macromolecules but in order for us to understand like what kind of

macromolecules we're breaking down we obviously know that it's like proteins and carbohydrates and lipids and

nucleated nucleic acids Etc but I wanted you guys to understand of like what kind of things that we're actually utilizing

that for so there's three particular processes by which cells bring in material

macromolecular material that needs to be broken down by lysosomes because in order for us to be able to break these

things down they have to be brought into the cell because the lysosomes are found inside of our cell so the question then

comes okay how do we get these things into the cell and what are those things that we're bringing into the cell and

how is that pertinent physiologically so first example here of how we're going to bring things into

the cell is something called receptor mediated endocytosis you're like what the stink

is this this is a really interesting process so it's it's kind of said within the name we're going to bring a

particular thing into the cell via a receptor so here's a receptor that's actually located on the cell

what happens is let's say whatever this may be maybe it's a protein that it binds with this receptor Maybe

it's a bacterium who knows maybe this is a particular bacterial antigen right so maybe there's a particular bacterial

antigen that's located on this that binds with this receptor or who knows maybe it's some type of like lipid

molecule maybe it's like a lipid molecule of some particular type but either way these molecules are binding

to these receptors that are located on the cell surface what happens is proteins called clathrons you know

there's what's called clathrin proteins what they do is they come and they bind to the cell membrane and they kind of

pull they use actin and pull the actual cell components here these receptors and all the things that they're bound to

into the cell and so what happens is you form like this little vesicle so what happens is you do this like little

endocytosis process and you pull into the cell this vesicle and here we have on here these receptors and then on

these particular receptors what do we have bound to it like we said we could have a bunch of different things it

could be proteins it could be some type of like lipid cholesterol molecule who knows or it

could even be like a bacterial antigen of some type so this is really important and then

once they get into the cell they then can combine with lysosomes a primary lysosome and then they can get broken

down now why would that be important and what kind of cells would this be important

I'll explain to you this could be important for example here I find this very interesting with um sometimes when

you're trying to do something called l d l receptor uptake sometimes whenever you have LDL

receptors and you need to down regulate those receptors in other words you don't need as many of those receptors

expressed onto the cell membrane we can bring them into the cell break them down or recycle them and then use them for

later so that's one example here so let's say that for example here's this LDL receptor uptake this could be an

example of something called down regulation and that's where we would bring these receptors into the cell

which they're bound to whatever it may be and have them get broken down and then we can use them later when we need

them that's just one example one example an even cooler example here is what's called you can see these on what's

called B cells so B lymphocytes so B lymphocytes are referred to as what's called antigen presenting cells

in other words let's say that this is a bacterial antigen that binds to a B cell receptor

the B cell receptor will then signal that and bring the bacterial antigens into the cell so that the B cell knows

hey this is a particular bacteria then they need to alert the immune system of so that's another really cool example

but there's an important terminology that comes from this when we actually take this endocytosis

process when we bring this whatever it may be this material into the cell this macromolecule material into the cell

whether it be through all of these mechanisms this process that it makes and it pushes these molecules into the

cell this vesicle now is a very important vesicle that we have to discuss this is now called a endosome so

this is called a endo sum so I want you to remember that okay

all right that's one particular mechanism the second mechanism by which we bring

things into the particular cell here is with this next one so let's say that you have this cell and

it wants to eat a particular bacteria or well maybe it's a virus maybe it's

even a virus of some type maybe it's a virus of some particular etiology

and it wants to bring these things into the cell what it'll do is it'll actually use

actin and kind of make these like things called pseudopods these little arms and it'll kind of engulf the bacteria or the

virus the pathogen in general and bring it into the cell so then what you get here is as it forms these things called

pseudopods it sucks this bacterian virus into the cell and it makes this vesicle that can contain within it the things

that it tried to eat and look at this look at this isn't that cool what is this process called and what

kind of cells would this be critical and important to know this is something that you want to know is called phagocytosis

and I'd say that this is probably one of the biggest indications and reasons for having lysosomes honestly so this is a

really really big one and this is pertinent in what's called white blood cells so this is really really important

for particular types of white blood cells what kinds of white blood cells things that you should know is things

like macrophages so things like macrophages another one is called neutrophils

neutrophils are another one another one is called dendritic cells these are really really common types of cells that

love to eat certain types of pathogenic material and bring it into the cell and obviously you

can understand that in this example I bring in proteins and lipids and carbohydrates and this one I'm bringing

in maybe a bacteria or virus that has nucleic acids their membranes could have lipids in them they could have proteins

that are involved in all of these structures and guess what I got the enzymes in my lysosomes that can break

all of them down so you see why this is a really cool concept all right the last one here is a really

interesting one and this is called autophagy this last one is called autophagy it's another way that we don't

necessarily bring things into our cells we just actually membrane membranize we form a membrane around already present

organelles and proteins that are defective and old inside of our cell that's already there so in other words

let's say here you have an old mitochondria all of these things are old they're defective they're just not

working as well anymore okay and so what happens is you actually start to form this membrane around these old defective

organelles and proteins so what I'm going to do is I'm going to start forming kind of a membrane this

makeshift membrane here and then what happens is after you form the makeshift membrane it'll eventually completely

membranize I hope that's a word membranize and enclose all of these particular organelles

when you do that that's really really important because you're kind of internalizing and forming a membrane

around these defective organelles that you want only those ones to get destroyed broken down we don't need them

anymore guess what lysosomes can break down proteins lysosomes can break down lipids lysosomes can break down maybe

nucleic acid molecules so I can break all of these things down an important terminology for both of

these so this one here where we actually so this one we called an endosome this one where we bring these particles in by

eating it it's called a phagosome it's called a phago so and this last one here where we actually

internalize old defective organelles and proteins this is called a Auto

phagosome if I go so this is really really important

now once we've done all of these particular processes we've now taken away of either bringing things into the

cell and enclosing them in a particular vesicle that confuse with the lysosome or things that are already old defective

in the cell we formed a membrane around them and now we can take these to the lysosomes so now this is the next step

my friend so now what we're going to do is we're going to take this phagosome this endosome and this autophagosome and

we're going to now fuse it with lysosomes so let's come down for a second

here we have the first one here is our endosome what we're going to do is we're going to take this endosome and we're

going to fuse it with a lysosome so each one of these this is going to occur here so we're going to take these and we're

going to fuse them together so you see how this is what's called your primary I'm going to write all these down here

this is your primary lysosome primary lysosome primary lysosome okay each one of these the endosome

the phagosome and the autophagosome are going to fuse with this primary

lysosome once it fuses with the primary lysosome guess what all of the enzymes in here the nucleases

the proteases the lipases the glucosidases all of these are going to break down they're going to rip that

stuff apart and they're going to destroy all the proteins the lipids the nucleic acids that are associated with the

bacteria the viruses maybe some of the lipids and proteins that are present from that we brought into the cell maybe

all of those things that are associated with organelles all of these things are going to get broken down

and as a result at the end of this after you've broken down all of these things this is what it looks like

you've now broken down all of this macromolecular material to maybe a smaller monomers or kind of small

residual particles you can do two things with this but we have to know a term now this term here is that this lysosome is

called we're going to point to this one this is called your secondary lysosome so your secondary lysosome is the

lysosome that's already fused with each one of these the endosome the phagosome the autophagosome and it's broken down

all that material that's present in them now a couple different terminologies here

before we go to the next step here whenever you take an endosome a phagosome an autophagosome Infuse them

with a primary lysosome and right when the moment of them fusing so this point here these are called specific types of

things that you have to understand the secondary lysosome is all the broken down products after these things are

fused but this point right here that I'm going to highlight so this is going to be one

is going to be 2 this is going to be three these have specific names this one here where the

endosome and the lysosome fused is called believe it or not it's not too crazy endo

lyso Zone okay this one here where the lysosome and the phagosome fuse this is called a phago

lyso Zone and this last one here where the lysosome and the autophagosome fuse is called a auto phagom lysosome not too

crazy and out of this world to understand those particular processes okay so with all of these we fused each

one of these things formed these intermediates after we form these intermediates they

broke down all the material all the macromolecular material and formed a secondary lysosome

the question then comes what can we do with all this residual material well I could have taken proteins and broken

them down into amino acids I could take lipids and break them down into fatty acids I can take nucleic acids and break

them down into nucleotides I can take carbohydrates and break them down into monomers so what I could do is I could

push and Export all of these different molecules such as

small carbohydrates such as small amino acids such as small lipids and Etc you get the point all of these can be pushed

out into the cell and they can be used in metabolic reactions so two things can happen with these they can go and they

can be used in metabolic reactions or they can kind of just sometimes believe

it or not sit there and they can make these kind of like little old inclusions and

sometimes we actually give this a very specific name we call it lipo fusion and you see this this is usually

representative the more you have of this lipofusion bodies in the cells it's more indicative of age increasing age

obviously that would make sense as you break more things down you're gonna have more lipofusion and so you can see this

very commonly in three particular organs one as you can have a lot of this lipofusion

in the heart or in the cardiac tissue you can have a lot of this in the nerve tissue

and you can have a lot of this in the hepatic tissue okay in the apotic tissue but this is something that you could

potentially see so if we push it out into the cell we can use it for metabolic reactions or store it as this

like lipofusion kind of material which is usually associated with increasing age let's write that down associated

with increasing age that's very prominent in these particular tissues the other thing that we could do is we

could take this secondary lysosome and say ah I don't need any of these things I'm going to go ahead and fuse this with

the cell membrane and then I'm going to release some of these materials out of the cell

so then what I can do is I can literally release I'm just going to draw a couple of these dots here I'm going to release

some of these molecules into the actual external environment this is sometimes kind of important

when we get into Immunology we'll talk about this later neutrophils love to do this neutrophils will take a bacteria

eat them up and then spit out some of their antigens and spit it into the lymphatic system so that it can go to

other immune system cells and they can pick it up sometimes your lysosomes will release

special enzymes believe it or not right out into the extra cellular fluid remember I told you that an osteoclast

bone tissue guess what they could release right onto the extracellular space and break down bone tissue they

can release acid phosphatases so you get the point here that what I'm trying to get is that we can take all of these

ways of bringing in macromolecular material into the cell once it's brought into the cell they fuse with lysosomes

make these intermediates they get broken down accordingly to each particular enzyme in the macromolecule the residual

lysosome is called a secondary lysosome it can spit things out or it can well I can spit it onto the cell or spin it out

of the cell that's the big things to understand the last particular function that we have to talk about lysosomes is

called autolysis all right my friends last part is autolysis so basically this is where the cell eats

itself that's essentially what it is so autolizes where the cell is literally eating itself so what happens is is

usually you have such extensive cellular damage so let's say that this cell has gone under extensive

cellular damage like Beyond repair extensive cellular damage

Beyond repair when that happens your lysosomes were seated receive a

pretty intense signal so let's imagine that you have extensive damage to the DNA you have extensive

damage to particular organelles you have extensive damage to particular proteins and what happens is after this extensive

damage occurs it then stimulates and activates these lysosomes it sends them powerful signals and you know what the

lysosomes do they're like oh shoot this cell is beyond repair we're going to have to we're gonna have to finish this

up and then what it does is it literally releases its contents all these nasty hydrolytic enzymes directly

into the cytoplasm now imagine having these hydrolytic enzymes that can literally break down every single

macromolecule just uncontrollably released into the cellular environment I have proteases

they can break down every protein I have lipase they can break down the cell membrane and the membranes of organelles

I have nucleases it can break down DNA RNA I have glucosidases it could break down

all the different types of carbohydrates this cell will literally start to eat itself and that is the process here

where this will undergo an intense process where the cell will literally cause cell

to eat itself eats itself I mean this is literally in layman's terms what's literally

happening and it's a pretty interesting process so it is a little bit different from something like apoptosis but again

this is when there's such extensive cellular damage Beyond repair that the lysosomes receive signals to release

their interest component their hydrolytic enzymes into the actual cytoplasm and start breaking down all

the different types of organelles this is autolysis and that covers the structure and function of lysosomes I

hope it made sense I hope that you guys enjoyed it and as always until next time foreign

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