Transcript
Use with ChatGPT / Claude Auto-scroll A
Introduces eukaryotic organelles and explains the endosymbiotic origin of mitochondria, including their bacterial-like membranes, genome, and ribosomes. Also presents the evidence and historical theory behind mitochondria and chloroplast evolution.
Speaker A
So we already discussed to some level the differences between prokaryotic and eukaryotic cells.Eukaryotic cells are distinguished from prokaryotic cells by the presence of membrane enclosed organell within their cytoplasm.The nucleus is the largest organelle.Those organelles provide discrete compartments in which specific cellular activities take place.Will concentrate on eukaryotic cells, animal cells, which are highly organized with many functional units, organelles.
And I would like to speak about some of them.I want to speak with you first about the mitochondria.The mitochondria is quite unique structure.It consists of two membranes.And I think that the most interesting things that related to the mitochondria as an organelle in eukaryotic cell is actually the fact that the origin of mitochondria is prokaryotic organism, a bacteria that enter the cell today.
It's quite clear that the mitochondria is a bacteria that was able to enter the cell like billion years ago.And from here the large cell and the small cell start to work together symbiotically helping each other.
So one of the way to look at this is what you see here in this photo.It's a bacteria and this is the mitochondria.So first from a general shape, the mitochondria resemble the shape of a bacteria such as E. Coli.
Well, E. Coli is a bacteria that also have two membranes.It's gram negative bacteria.And those bacterial cells have two membranes.
And although we are not absolutely sure it looks like that the mitochondria and also chloroplasts were evolved from a bacteria with two membranes.There are other suggestions that suggest that the bacterium will have one membrane.There are other bacterial cells that have one membrane which is gram positive bacterial cell.And the other membrane was coming from the cell billion years ago.So that's the way that we turn into an organism that have two membranes.But I think that probably it's quite reasonable to suggest that the mitochondria with its two membranes were evolved from gram negative bacterial cells that have two membranes.Another thing that we can see in the mitochondria is that this is an organelle with its own genome and its own ribosome.So the genome of the mitochondria have a general structure like the genome of bacterial cells.Bacterial cells has usually one circular chromosome.
And that's what we have in mitochondria as well, circular genome as well.
Some mitochondrial genes are expressed and translated in the mitochondrial ribosomes, which are quite similar to bacterial ribosomes bacteria, eukaryotic cells, they're all using ribosomes for protein translation.However, the shape, the size of the bacterial ribosome is different as compared to eukaryotic ribosomes.In general, bacterial ribosomes are smaller in size versus the eukaryotic ribosomes.And the mitochondria have similar size ribosomes similar to the bacterial ribosomes.So it's another way to look on the mitochondria as a bacteria that was captured in a large cell.
And many things were kept as they were billion years ago.The genome, the two membranes, probably the ribosomes that we have, are pretty much bacterial ribosomes in their structure.And they are being used for translation of mitochondrial products.
So when we are putting together the origin of the mitochondria, we can see that there are quite a few similarities between the mitochondria and bacterial cells.Mitochondria are the descendants of some bacteria which was endocytosed by larger cell probably 1 billion years ago, but not digested.And actually we have those type of situations even today.I mean, if you are looking into a bacteria named Listeria, and this is a pathogen that can enter into cell and it also know how to escape the activity of the cell that try to digest the bacteria.So the bacteria is infecting cells.
The cells cannot really deal with this bacteria by destroying it.The bacteria is running from one part of the cell to another.Listeria type of activity is probably what we had billion years ago when we had a bacteria enter into a large cell.
Reviews the structural and genetic similarities between mitochondria and bacteria in more detail. The section closes by introducing the classic endosymbiosis theory and its support from mitochondrial and chloroplast DNA.
Speaker A
The mitochondria have many similarities to bacterial cell, similar size and shape to prokaryotic cell.In terms of the size of the mitochondria, which is an organelle inside the eukaryotic cell.Well, I mean, it's more or less the size and in general the shape of prokaryotic cells.Double membranes, like some bacterial cell, circular DNA.Again, organelles in general don't have their own DNA.
That's a very unique example.
Those genes that are expressed by the DNA have no introns.That's another thing that makes them to look like genes that are bacterial genesis small ribosomes as compared to the size of the cytoplasmic ribosomes in eukaryotic cells.And when we are talking about antibiotics that can inhibit bacterial cells, well, we try to make antibiotics which are working on small ribosomes, the real cells that can infect us.And they are not going to help.They are going to be selective and not to target the large Ribosomes.
However, here we have a problem.We don't want the small ribosomes of the mitochondria to be affected by those type of antibiotics, because this is part of us.And we want the selectivity to even distinguish between small ribosomes of bacterial cells that are infecting us, versus not to react against small ribosomes that are found in the mitochondria.We need the mitochondria for many reasons, as you're going to see soon.
So, in general, the mitochondria is very, very likely to be a bacterial cell that enter the large cell before nucleus or after nucleus.That's not really clear.But what we start to have is symbiotic effect in between two cells that found that one cell can give the other quite a lot.And they kept living together ever since.
Speaker B
In 1981, Len Margulis proposed that current eukaryotic cells evolved from a grouping of cells.A large anaerobic, prokaryotic predatory cell likely engulfed an aerobic bacterium.The bacterium becomes surrounded by a vacuole made of the predator's cell membrane.The predatory cell is unable to digest the bacterium, which persists in the cytoplasm of its host.The combination was mutually beneficial to both organisms.
Over time, the two cells became dependent on each other and the engulfed aerobic bacteria evolved into mitochondria.The predatory cell may also have met and engulfed a photosynthetic bacterium.The photosynthetic bacterium also becomes surrounded by a vacuole made of the predator's cell membrane, and the predatory cell is unable to digest the bacterium.Over time, the two cells became dependent on each other, and the engulfed aerobic bacteria evolved into chloroplasts.Why do we think the endosymbiosis theory may be true?
Mitochondria and chloroplasts cannot be formed in cells that lack mitochondria or chloroplasts.The cell's DNA does not have the genes necessary to code for the proteins that make up the mitochondria or the chloroplasts.Mitochondria and chloroplasts each have their own DNA that's very similar to prokaryotic DNA, and they have the ability to synthesize those proteins necessary to create new mitochondria and chloroplasts.
Speaker A
This animation is from W.H.riemann Collection.
Explains the main function of mitochondria in ATP production and cellular respiration. The speaker describes the inner membrane, proton gradients, and the battery-like mechanism that powers ATP synthesis.
Speaker A
So let's talk a bit about the mitochondria.The function of the mitochondria.There are many functions.I'm not going to cover all of them.But I want to speak here on about two.
Right now I will talk about the ATP production, the cellular respiration that the mitochondria is involved with.And that's actually the creps, the citric acid cycle, which is part of the cellular respiration.So the mitochondria is responsible for generating most of the useful energy in the form of ATP, which is derived from the breakdown of lipids and carbohydrates, proteins as well, apoptosis program, cell death.And here you're going to see that mitochondria is involved as well.
So first, the mitochondria is involved in the process of ATP reduction.
So mitochondria is involved with releasing the energy of food molecules.This energy is expressed as proton gradients.
And the inner membrane of the mitochondria contains a complex of enzymes which are transforming the energy in the proton gradients into chemical energy stored in ATP.
So this is ATP, adenosine triphosphate.The ATP is required for many cellular activities.
One of them, of course, it's energy releasing energy.The ATP bonds are, when they are broken, they are going to release energy.But ADP is not just about energy.It is also nucleotide, a adenine that we are using for RNA synthesis.And after the modification, after it is modified, it can be used also as a deoxyribose, in other words, as the A for the DNA.
So that's another thing that we are getting from ATP.ATP is an important cofactor of many enzymes.We are using ATP for phosphorylation of tyrosine, serine, threonine residues, which actually make a huge difference in the activity of proteins that are being phosphorylated in such a way.The mitochondria is an organelle with two membrane, the outer membrane, which is quite smooth and it allows small molecules to pass through this membrane.And the inner membrane, which is strictly regulates the type of molecules which can move across.
It's highly folded, see it here.But you can see it even better in this electron microscopy.
It's highly folded to increase surface area.So we want as much as possible, surface area of the mitochondria in order to have a place for a lot of reactions that are making ATP.For making ATP, we need an organelle which have two chemical environments, one which is between the outer membrane and the inner membrane, and the second one which is inside the inner membrane.In general, the structure of mitochondria look like this, an organelle with two membranes.And in this organelle you have two chemical environments.
One of them is represented by the green.The other one is represented by the yellow color.The outer membrane is fairly smooth and the inner membrane is more strict in regulating things that are getting in and out.
And the matrix here, this green part, is the components enclosed by the inner membrane.Well, the energy that the mitochondria is making is based on using two compartments.Actually we are doing it all the time.Your cell phone, my microphone, all of those things are powered by something that give you an energy by using two compartments.It's a battery.
Battery have two compartments.One of them is positively charged, the other one is negatively charged.And electrons from the negative portion are moving to the positive part.And as they are moving, they are producing energy.So again we are talking about a system that is using some sort of gradient of certain things here, of electrons that are moving from high concentration to low concentration of electrons.
And by doing so they are making energy.I wanted to watch a short video which is describing making energy by two gradients.
Uses an animation and textbook explanation to show how electrons and protons create a gradient across the mitochondrial membrane. The section details how ATP synthase uses that gradient to convert ADP into ATP.
Speaker C
Our body is made up of trees, trillions of cells.They all require energy to function.This energy is created within our cells in the mitochondria.Here food is converted into chemical energy called ATP.ATP is released by the mitochondria so cells can use it.
Mitochondria consist of two an outer membrane separating it from the the cytosol and an inner membrane surrounding the so called matrix.The area between these membranes is called the intermembrane space.
ATP is generated at the inner membrane of mitochondria by an efficient mechanism called oxidative phosphorylation involving several membrane protein complexes.
Nutrients provide high energy electrons in the form of NADH which are used by the protein complexes to pump protons from the matrix to the intermembrane space.
This continuous pumping creates a proton gradient where the positively charged protons are attracted to the more negative matrix.
When the protons re enter the matrix through the ATP synthase protein complex, they catalyze the production of ATP.
Speaker A
A couple of lectures ago I gave you this as an example for a combination of active and passive transport of molecules which are linked together in order to make ATP.
So let's go to the textbook.So here we are talking about two different stages.First we.The first stage is to make the gradients of protons of hydrogens.And the second one is to use this gradient in order to make ATP using this ATP synthetase.
So the net flow of molecule here is always down the concentration gradients from a Compartment of high concentration 1 with lower concentration of this molecule.So this what we learned when we talked about the movement of small molecules in a passive way.So gradients create a potential energy which can be used in biochemical activities.So here in the mitochondria, using energy from food gives the energy for active transport of hydrogen ions, protons by hydrogen pumps.So that's the first the active portion of this activity.
So this create high concentration of hydrogen on one side of the membrane versus the other side.And from here the gradient drives the rotation activity of the ATP synthetase which lead to ATP production.
So the net flow of molecules is down the concentration gradient and that create a potential energy allow rotation of the ATP synthetics.
So what I would like to do now is to go to this animation and to give you the general idea how this process is to take place.So the energy associated with the gradient is used for synthesizing ATP from ADP and PI.
So.
This is the mitochondria.Here you can see the two membranes, the inner membrane have the system which allow first to develop the high concentration of hydrogen on one side of the membrane and the 80% tails to use this gradient.
So, So the ADP synthetase is using the high concentration of the hydrogen that was developed by the other system by the pumps, by the hydrogen pumps.
So the high concentration of the hydrogen is in between the two membrane, the INL and the outer membrane.That's where you're going to find the high concentration of the hydrogen.And from there they are moving to the matrix by using the ATP silted tails on the way they are activating it, they are turning it around like a motor.And that's actually the power which is making the ATP for us.
So the bit is helping making the ATP synthes to rotate.
So what you see here is the hydrogen ions, their high concentration.What you see here is PI and this is adp.The product is going to be ATP.
So ADP and this is the product after all, ATP.
So for every three hydrogens move downstream, downstream the gradient we get one molecule of ATP.So every time that the hydrogen moves from high concentration to low concentration, we are getting a portion of the ATP synthesis activated in order to turn the ADP into ATP.And that's the product that we need.So that's the activity which is induced by the high concentration of hydrogen, the gradient of hydrogen which can cross the membrane throughout the ATP synthetase.And that's what give the ATP synthetase the ability to make a TP from ADP npi.
Covers mitochondrial genome structure, maternal inheritance, and why mitochondrial DNA is useful in tracing ancestry. It also explains how mitochondrial mutations can contribute to disease, aging, and optic neuropathy.
Speaker A
So the mitochondria has a circular genome that's what we mentioned earlier.It genes are expressed and translated in mitochondrial ribosomes.The product are mainly proteins that participate in a mitochondrial function.And certain regions, the D loop over here is not making proteins and it is not highly conserved over the evolution and can serve as a tool to look for differences between closely related species.The mitochondria genome is transmitted by eggs, not sperm, to the next generation.
And accordingly it represents maternal line, mother to daughter to daughter, where sons are the dead end for mitochondrial DNA.They cannot transmit this DNA to anybody else.So that's the reason that when we are checking mitochondrial genomes, what you see is the maternal line, the female line, mother to daughter.And there are many implications for this.I mean, when we try to sequence certain organisms.
First of all, we are using a mitochondrial genome because we have a lot of mitochondria in each cell.So you have a lot of this genome there as compared to the one set, actually diploid set of the genes that we have in the nucleus.So a lot of time like sequencing the Neanderthal tarts led us first of all to check for the mitochondrial genome and for example to try to see how the Neanderthals are related to Homo sapiens.And that's actually one of those things that we can do by using mitochondrial DNA looking for the tree of life related to certain organisms.Although we need to know that we are using only the maternal line, while the DNA in the nucleus, both maternal and paternal line.It's actually everybody is involved in this stage.
So human mitochondrial DNA is a single circular chromosome with 16 unworth 569 base pairs.Each mitochondrion contain 5 to 10 copies of the mitochondrial chromosomes.So after all, since we have hundreds of mitochondria in each cell, you can get something like thousand molecules in one cell.The mitochondrial DNA is mainly coding the DNA and it's small.There are quite a few proteins that you want to make from this DNA.
And the non coding, which is mainly regulation, is usually very very restricted as compared to what we have in the nuclear genome.That only 1.5% is a coding region.The 93% that is coding is regions are responsible for make for 12 genes.The rest is control region.7% is about controlling the expression of those genes.
A few more things about the mitochondrial DNA contain genes for ribosomal RNA transfer RNA some all of the proteins related to oxidative phosphorylation and electron transport.Now you probably can imagine that the mitochondrial DNA is not enough for all the activities of the mitochondria.Many of those genes that their product is being used in the mitochondria are from the nuclear chromosome.So this is a very nice symbiotic relationship.The mitochondria can actually enjoy the fact that it's in another cell, larger cell, with more space on the DNA for all the things that mitochondria meet.
So most of the proteins that are being used by mitochondria are made by nuclear chromosomes.So we have a good relationship.We are making the product for this bacteria that is inside our cell and they are in turn making for us the ATP and a lot of other things.
So how mitochondria is inherited.The genes of the mitochondria are responsible for some specific phenotypes.And again, mitochondria inherited from the mother only affected males.If you have a certain type of mutations in your mitochondria, males cannot transmit those traits to any of their kids simply because they do not have the ability to transmit this mitochondrial DNA.So they are the dead end for this DNA.
If they are going to survive and they want to have kids, they are not going to suffer from the same conditions.
A relatively unprotected and unrepaired, not like the nucleus that have all the activities related to DNA repair mechanisms.Mitochondrial DNA suffers more than 10 times the damage that nuclear DNA does.In general, major defect in mitochondrial function is usually going to be lethal.It's going to kill at the level of early embryonic development.So most affected embryos would die before birth.
However, we have some mitochondrial diseases that can affect different parts of the body and that can lead to cancer and to aging.The mitochondria is involved with the process called apoptosis, programmed cell death.And cancer is related to this type of phenotype.When apoptosis is not working appropriately, we can have cancer and aging.It's actually the other way around.
When there is too much cell death, the aging process is going to be accelerated.
So there is one specific disease that we know quite well which is involved with mitochondrial mutations.It's called the liver hereditary optic neuropathy.And this is a sudden and irreversible loss of sight.Vision loss result from the death of cells in the nerves that rely the visual information from the eye to the brain.It's part of the optic nerve.
And we know about several genes which are involved with this process and the one and the four genes that are made by the mitochondria.So there is at least one significant direct disease which is induced by mutations of the mitochondria.
Introduces the nucleus as the largest organelle and discusses possible ideas about its evolution. The speaker then explains nuclear DNA organization, the nuclear envelope, pores, and the nucleolus.
Speaker A
Okay, I Want to move to another organelle, the largest organelle that we have in animal cell.And this is the nucleus.How the nucleus was evolved, it's not very clear actually in the last few years when we found that there were some viruses that are infected.Amoeba is unicellular organism that are extremely complicated as compared to any virus that we knew about it earlier.And in many ways you can find similarities between this virus or few viruses actually Mimivirus, Pandora virus and others that actually can make them like a nucleus in some ways.
So although we don't really sure about this, it's not 100% clear those viruses were actually just found not very long time ago.But one of the idea to ask yourself how the nucleus was evolved is quite complicated organelle and have quite a specific structure as you are going to see in a second one of the idea.It's actually similar in some ways to the way that mitochondria was evolved by something that was able to enter into a large cell and actually start to help the cell to do better.So when it comes to the nucleus, this is one of the direction that we have today, although we are still not there.
So the nucleus, few words about the nucleus.This is the largest organelle, the genome, Our genome.DNA is packed there into chromosomes.
The nucleus membrane allow gene expression to be regulated by post transcriptional mechanisms such as splicing.So this is in general the structure of the nucleus.
So the nucleus contains DNA, RNA and proteins.Rna?Yes, I mean the DNA is expressed in the nucleus into rna.So you are going to find RNA there as well.
So the DNA is packed into chromosomes and during the time when the cell is resting, not during cell division, they're going to be located when they are bound to the inner portion of the membrane of the nucleus.
So the nuclear envelope surrounding the nucleus consists of two membranes.So this is the envelope here is made out of two membranes.They're actually arranged as a sac, so it's directionally connected to each other.But when you are looking on every site on these nucleus, you are going to see two membranes.
So the nuclear envelope is bound to the chromosomes, the outer membrane of the nucleus, the inner membrane of the nucleus.And in between each sac you have the nuclear pores.
So this envelope which have those large pores, they allow many large molecules to get in and out, such as RNA molecules.After RNA is going to be fully mature, it can get out of the nucleus, proteins can get in, can get out of the nucleus.And the presence of the nuclear nucleus membrane allow genes expression to be regulated by post transcriptional mechanism such as splicing.
The chromatin.The chromosome is attached to the inner membrane and here you see the nucleus.The nucleus is a spherical body located within the nucleus and it is actually making the ribosome.It helps to assemble the.The ribosomes contain mainly RNA and proteins and here they can be assembled into the small and large subunits of the ribosome.
And here you see the rough endoplasmic reticulum which is connected to the nuclear envelope.Like you can see it here, it's actually an extension of the nuclear envelope in a way.
So on the endoplasmic reticulum, on the rough endoplasmic reticulum you see the ribosomes.So ribosomes are assembled in the nucleolus.They need the permission to get out through the nuclear pore and then they are going to be found in the cytoplasm.And from time to time, depending on the protein that they are going to make, they can be integrated with the endoplasmic reticulum.With the rough endoplasmic reticulum again, we'll talk about it quite a lot.
Explains how proteins are sorted and directed to the correct cellular destination. This section introduces free and membrane-bound ribosomes, the rough ER, and the movement of proteins toward the Golgi apparatus.
Speaker A
Sorting and targeting of proteins because of the complex internal organization of eukaryotic cells, the sorting and targeting of proteins to their appropriate destinations are essential tasks.Protein need to be delivered to the correct organelle.Let's start with a short introduction from Biovision.
Speaker D
Pores in the nuclear envelope allow the import of particles containing MRNA and proteins into the cytosol.
Here, free ribosomes translate the MRNA molecules into proteins.Some of these proteins will reside in the cytosol.Others will associate with specialized cytosolic proteins and be imported into mitochondria or other organelles.
The synthesis of cell secreted and integral membrane proteins is initiated by free ribosomes which then dock to protein translocators.At the surface of the endoplasmic reticulum, nascent proteins pass through an aqueous pore in the translocator.Cell secreted proteins accumulate in the lumen of the endoplasmic reticulum while integral membrane proteins become embedded in the endoplasmic reticulum.Membrane.
Proteins are transported from the endoplasmic reticulum to the Golgi apparatus by vesicles traveling along the microtubules.
Speaker A
So ribosomes found in two locations in the cell, three ribosomes which are present in the cytosol and membrane bound ribosomes which are attached to the rough endoplasmic reticulum 3 and membrane bound ribosomes produces different proteins.
Three ribosomes produce proteins used inside the cell itself or to migrate to other organelles such as mitochondria and nucleus.
Membrane bound ribosomes produce proteins that are going to be packed in secretary vesicles.
They are going to be exported from the cell or to be integrated in the membrane.
The other option is for those vesicles to turn into lysosomes.Proteins that are going to be secreted from the cell, all going to be integrated in the plasma membrane or are going to have some other roles required to be made by radio ribosomes which are bound to the ER, endoplasmic reticulum.
So I would like to speak with you now about the endomembrane system which start with the endoplasmic reticulum, then the vesicle are going to move to the Golgi apparatus and then proteins are going to move as vesicles to their destination.
I would like to talk with you about the endoplasmic reticulum.Now we are going to speak mainly about the RAS endoplasmic reticulum.It is rough under the microscope because there are a lot of ribosomes there.The main role of the rough endoplasmic reticulum is to be involved in making proteins.But actually there is another portion of the endoplasmic reticulum that smooths endoplasmic reticulum without ribosomes, but it is involved in lipid and steroid hormone synthesis.
The smooth AR is involved with a lipid metabolism such as making steroids molecules, cholesterol, testosterone and phospholipids for biological membranes.And they are extremely important.Those cells that are making for us, those type of steroid hormones are containing a lot of the smooth ER, and that can be their main function.But I want to speak with you mainly about the rough endoplasmic reticulum.And this is a system which is involved with protein translation, folding and processing.
And those proteins are going to be sent in vesicles to the Golgi apparatus.
Speaker B
Two membranous organelles, the Golgi apparatus and the endoplasmic reticulum or er, are the main components of the cell's endomembrane system.A primary function of these organelles is to produce mature proteins that will be exported from the cell, incorporated into membranes or moved into other parts of the endomembrane system.For simplicity, we'll describe these organelles from a two dimensional point of view.New proteins made in the ER either enter the lumen of the ER or are embedded in the membrane inside the er.Enzymes add sugar groups to some of the proteins, creating glycoproteins.
The ER directs its proteins to the Golgi apparatus transport.Vesicles bud off from the er, taking with them a cargo of membrane and lumen proteins.The vesicles fuse with the Golgi apparatus, adding to the Golgi volume and protein content.The sacs of the Golgi apparatus are called cisternae.The part of the Golgi apparatus that lies nearest to the ER is the CIS region.
The part nearest the plasma membrane is the trans region.The middle cisternae make up the medial region.In one model for protein transport within the Golgi, the proteins are delivered in vesicles from one compartment to the next.Each compartment contains Golgi enzymes that perform modifications to the proteins.For example, in this particular sac, a sugar residue is cleaved from proteins.
Mature proteins in the trans region of the Golgi are packaged into vesicles in preparation for travel to their final destination.In this case, proteins are targeted to the plasma membrane for secretion outside of the cell.
Describes the Golgi apparatus as the cell’s sorting and packaging center. The speaker explains vesicle budding, cisternae, protein modification, and how cargo is sent to membranes, secretion pathways, or lysosomes.
Speaker A
Well, from the endoplasmic reticulum, we are going to move to the Golgi apparatus.
Well, the Golgi apparatus is based on vesicles.The way that proteins are reaching the Golgi apparatus and the way that they are moving from the Golgi apparatus is based on vesicles making vesicles and letting vesicles to be fused with larger membranes.Vesicles are carrier of molecules in the cell from the ER to the Golgi apparatus, for example.So the first step is that the protein need to move from the ER to the Golgi apparatus and the process is involved, pinching out vesicles from the ER to be fused in the Golgi apparatus.The vesicle is formed, it's going to be disconnected to reach the target compartment and to be fused with this target compartment.
And everything which is inside the vesicle is going to be inside the target compartments.Proteins which are going to be integrated in the membrane are going to keep their orientation when they are getting into the target compartment.So this square structure is going to be outside in the donor compartment, but it's going to be found the same way in the target compartment as well.And they're going to be outside in the vesicle as well.So if this is a protein that you, you can see it here.
Again, the square part is outside facing the cytosol is going to stay facing the cytosol when it comes to the vesicle or when it comes to the target compartment.So the transfer of material by vesicle is based on vesicles budding from compartments donor and moving to the following compartment recipients carrying inside the molecules to be transferred.This way, the cargo is moving from one lumen to another lumen of the next compartment, when all the orientation of the molecules outside or inside are going to be kept.Here you can see this again.Membrane.Both the lipids and the embedded proteins, integrated proteins that you have from the donor compartments are transferred to the target compartment and preserve in the target compartment membranes the asymmetric orientation that they had before.
So the extracellular region in the donor compartment will retain extracellular in the target compartment as well.
So here, as we know as vesicles are being formed, we can go to the Golgi complex, which is based on vesicles fusion and vesicle assembly, the Golgi complex.
It is important that translated proteins are delivered to their specific cellular location.To accomplish this, the protein need to be transferred to the Golgi apparatus.The Golgi apparatus is the sorting organelle, the post office of the cell.And this is because the Golgi apparatus receives protein from one location and target them to other locations.
So what is the structure of the Golgi apparatus?
The Golgi consists of flattened membrane sacs that contain enzymes ready to modify proteins for shipment to their specific locations.
So the proteins from the rough endoplasmic reticulum are sent to the Golgi.As the protein move throughout those Golgi apparatus sacs cisterna, the protein is going to be modified by enzymes and eventually it's going to be packaged into vesicles which are going to send the protein to its appropriate location.
So the Golgi apparatus is made out several cisternas.First the C. Cisterna located close to the R, followed by the medial and trans cisterna, and at the very end, the trans Golgi network.
So the protein is going to move throughout those cisternas and when it reaches the trans Golgin network, it's going to be packaged into vesicles and to be transported to the appropriate location.
And the process start at the er.At the er, the protein is going to to be encapsulated by a vesicle and to move to the Golgi apparatus.
And over there the cis cisterna is going to be formed by fusion between those vesicles that contain the protein inside.And the proteins are going to move throughout the system.And to be modified by enzymes.And that's the way that they are going to reach eventually to the trans Golgin network when they are going to be sent to their appropriate location.
So protein are going to be sorted throughout the trans Golgi network and are going to be grouped together.
And vesicles which are formed from each part of the trans Golgi network are going to take their cargo to the appropriate location.
So that's the general idea that by which protein in the C. Cisterna are going to reach eventually into the trans Golgin network where they are going to be packed into vesicles to be transmitted to their appropriate organ.They can be sent to make lysosomes.They can be sent to the membrane of the cell.Those proteins can be integral membranes or to be secreted out of the cell.
So the Golgi apparatus main function is the final packaging location for proteins.
It is involved with modifying molecules by enzymes.
Carbohydrates groups are attached package them into small membrane bound sacs, vesicles and those vesicles.But from the trans Golgi network of the Golgi complex, the TGN final mature proteins are moved to their destination which can be the membrane for secretion or integration in the membrane.
Covers lysosome function, acidic activation of digestive enzymes, and roles in autophagy and phagocytosis. The section ends with programmed cell death, necrosis, and how lysosomes contribute to tissue damage and development.
Speaker A
What's going to dictate this is actually what's happened in the error.If the protein enter the lumen of the ar, it's going to be secreted from the cell.Or if it's going to.If it is integrated in the membrane, it's going to stay in the membrane later on.So it's going to stay as membrane protein for its entire life.And the other destinations can be endosomes that are maturing to lysosomes.Lysosomes are the cells garbage disposal system, the cleanup crew, the source of lysosomes.They bud off the Golgi apparatus.
They are breaking down molecules into their best components Using strong digestive enzymes.
They can digest food and waste material within the cell.Worn out organelles such as mitochondria as an example.
And there are very important players in the immune system.Lysosome degrade bacterium that is taken by phagocytosis.Our phagocytosis is mainly the activity of macrophages neutrophils which are part of the immune system.But there are unicellular that are using phagocytosis in order to eat in order to pick up bacterial cells and to use them as food.
This introduction was made by McGrew Hill.
Speaker E
Lysosomes are membrane bound Vesicles that contain hydrolytic enzymes.These enzymes digest particles or cells taken into the cell by phagocytosis.They also digest old organelles such as mitochondria.The hydrolytic enzymes that degrade proteins, nucleic acids, lipids and carbohydrates are formed, formed in the endoplasmic reticulum and then transported to the Golgi apparatus by transport vesicles.
The lysosomes arise from the Golgi apparatus when particles such as viruses or bacteria are ingested by phagocytosis.The lysosome fuses with the particle containing vesicle called a phagosome and delivers the hydrolytic enzymes.Lysosomes also fuse with organelles such as defective or worn out mitochondria.This results in the destruction and recycling of these structures.
Speaker A
So lysosomes, as I mentioned earlier, the source of lysosome is the Golgi apparatus.
It is an organelle with a single membrane.Inside this organelle you can find many hydrolytic enzymes, like 50 enzymes.You can put pretty much destroy every type of molecule that you have in the cell if it is inside the lysosome.And those enzymes are activated by low ph.
So the lysosome enzymes are activated by low ph.They carry hydrolasers that degrade many different things, clearotides, proteins, phospholipids.And you want to have some control over their activity.You want to have a very strict control.And the strict control to make sure that they are going to work only in the lysosome is the low ph that you have there.
You have approximately a pH of 5.5, which is acidic ph.And those enzymes that are going to be in the lysosome are going to be activated by the low ph.And that's quite important because if they leak out of the lysosome or if they are secreted outside of the cell by accident, or in the case of a disease, they're not going to be active in ph 7.2, that is the normal ph that we have in our system.So although they are going to be out, they are not going to cause the damage.And they can be activated only when the pH is low 5, 0.5 or so.
One important function of the lysosome is auto fagging, which is killing things or destroying things that are inside this housekeeping function.For example, removing one organist like mitochondria, the lysosome is going to be fused with the mitochondria.And to put all those strong Digestive enzymes inside the mitochondria.And this way the mitochondria is going to be destroyed.Heterophagi, which is destroying cells from the outside of the eukaryotic cell.
So the lysosome destroy other organisms like bacteria.After phagocytosis, after the bacterium is enclosed by vesicle, it's called the phagosome.Vesicles containing lysosomal enzymes fuse with it.The bacteria is subjected to low ph and activated enzymes that degrade the bacterium.The bacteria is food also for many eukaryotic cells.
So when in our system, the phagocytosis and the destruction of content of the phagosome by the lysosome here, it's a matter of an immunity.The immune system works this way.But when it comes to many eukaryotic unit cellular cells, you are going to see the same activity, but for different reason.Here the bacteria is going to serve as a food to those microorganisms, tetraimina and other unicellular eukaryotic cells.So that's actually the same idea.And interestingly, the systems here are extremely similar because between unicellular eukaryotic cells and macrophages, despite the fact that we have almost billion years apart in the evolution in between us.But this system is pretty much the same in both cases.
So other activities that lysosomes are going to be involved with this is with programmed cell death.See, I mean those fingers that you see here in this frog certain point, it was not look like fingers, but it was look like some sort of a bow at the end of the hand over here.Now, in order to make those fingers, you need to kill those cells that are located over here.And lysosomes have quite a lot of activities that are related to this type of a program cell death.
And that's also the way that we are being developed.Our fingers are being developed in a similar, with a similar way.So lysosomes are associated in program cell death during embryonic development and also in other stages.Programmed cell death is involved among other things with recycling of cells.
Unprogrammed cell death is in those cases that we have sudden damage, for example, lack of oxygen to the heart.Now this is not the regular program cell death.It's also called necrosis.This process called necrosis, it's not involved with the same level of sophistication of different proteins talking with each other.It's a damage that lead to a lack of oxygen.
Damage that is involved with lack of oxygen can lead to the death of cells in a less organized way.But still, the lysosomes have a lot of things to do in this stage as well.Non programmed cell death, such as cardiac ischemia, lack of oxygen as a result of blockage of the blood flow.In myocardial infarction, the lysosomes can kill the affected cells.In some cases, that's actually the damage that we have in the heart.
Sometimes the myocardial infarction by itself is not causing the real damage that takes place afterwards by too much cell death.More than we need, actually.