 Something bad has happened. A double-stranded RNA virus has entered your body. It's now on its way to your cell where it's going to inject its nucleic acid into your cell and then produce a boatload of virus babies. At least that's what we are expecting right? Except it turns out that no virus babies are made. When the viral double-stranded RNA enters your cell or it's injected into your cell, it's supposed to integrate itself with your DNA so that it can produce this mRNA strand which will eventually give you viral proteins. Now these viral proteins are super essential for the formation or for the production of the virus babies. So that means that something is disrupting this entire process in such a way that these viral proteins are not made at all. So if there are no viral proteins, there are no virus babies. So let's dig deep and find out what is this something and how is this disruption really working. Let's take a closer look at the cell and all of these components that I've drawn out. So this is our virus right over here and it has injected that double-stranded RNA right into your cell. So this is the double-stranded RNA. Whenever the cell senses this viral RNA in its cytoplasm, an enzyme out of nowhere will show up and start chopping this viral RNA into small pieces. This enzyme it's called Dicer. So this pink colored blob right over here, this is the enzyme Dicer and it's going to chop off this really long RNA into really tiny pieces. So after chopping off, it's going to look something like this. So we're just chopping it off. So now you have like really smaller pieces of this longer double-stranded RNA. Now this chopping whenever Dicer chops it off, this chopping leaves behind something that is recognized by this yellow blob over here. Now this yellow blob is a multi-enzyme complex. So think of it in this way that whenever Dicer chops off the longer RNA, it leaves this neon sticker at the end of each chopping and this neon sticker is recognized only by this yellow-colored multi-enzyme complex. So the minute it sees any tiny RNA or any small piece of RNA with that neon sticker, it's going to quickly bind itself or bind that piece of RNA with itself. Now once these smaller RNA pieces are loaded on to this multi-enzyme yellow-colored complex right over here, it's going to split the RNA into its strands. So remember this is a double-stranded RNA. I'll just write it down so nobody forgets, including me. So if this is the double-stranded RNA, it's chopped down and these are still double-stranded. So let's remember that and when it is split apart, these two strands, they completely separate. So one of these strands, it runs in the 5' 3' direction and this is the sense strand. So this is the sense strand and there's another strand which runs in the opposite direction and this is called the anti-sense strand. Now what this complex is going to do, it's going to get rid of this sense strand and hold on to this anti-sense strand. Now can you guess why that is so? Why are we sticking with the anti-sense strand and not with the sense strand? Why can't we reverse this whole thing? Why can't we get rid of the anti-sense one and stick to the sense strand instead? Well, so you see that this complex, it has a purpose for this anti-sense strand. What it's going to do, it's going to use this anti-sense strand as a guide and look for its complementary mRNA. Now if you remember in DNA replication, we had a coding strand and a non-coding strand. So the non-coding strand is the anti-sense strand. That's the one that we use as a template to produce an mRNA. So if over here I start writing it down, so okay. So if this pink one is the anti-sense strand and then this anti-sense strand will act as a template to which an mRNA strand will be formed. So if this is the anti-sense strand then this is the mRNA strand. So in that case what will happen, this anti-sense strand is running in the 3 prime 5 prime direction. So the mRNA strand that will be produced, it will run in just the opposite direction and it will have the complementary base pairs to this anti-strand. So which is why this mRNA will bind with this anti-sense strand. It's complementary to one another because of the base pairs or the complementary base pairs. So similarly, and this was the anti-sense DNA that we were talking about. So similarly, this anti-sense RNA, let's not forget this is an RNA, so this anti-sense RNA works in a very similar manner. So this anti-sense RNA will look for its complementary base pairs in the mRNA sequence and look for that mRNA which is complementary to it. And once it finds it out, it's going to bind to that mRNA. And if we had chosen the sense strand instead, then this sense strand will never be used as a guide or it will never act as a guide because this sense strand and this mRNA strand, they will have the same base pairs. How will it even bind, right? They are, they both work in the same, they are both working in the same direction or they run in the same direction. And at the same time, they have the same complement, the same base pairs. So the sense strand will never work, but the anti-sense strand will. So because of this relationship that it has, the anti-sense strand will quickly find the mRNA sequence which is complementary to it. And once this, and why do we need to even find this mRNA strand at all, right? This complementary mRNA strand because we want to get rid of this strand completely. So once the complex finds out or once the complex uses this anti-sense strand to find the complementary mRNA, it's going to release these certain types of enzymes. Do you see this pink colored scissors I've drawn out? So this is a type of enzyme called slicer. So I'll just type it down. This is slicer. I don't know why I keep saying type, it's writing it down. Anyway, so this is the slicer enzyme and what it's going to do, it's going to chop off this mRNA into pieces. And if this mRNA is chopped off, these viral proteins won't be produced at all. So if there are no viral proteins, there are no virus babies. So do you see what really went down? Not only are we eliminating this double-stranded RNA that the virus had injected into our cell, but we're also getting rid of any mRNA that can possibly produce viral proteins. So if this virus was sneaky enough to still have some mRNA produced, we are also getting rid of that. So there's no mRNA, no double-stranded RNA left anymore, no viral proteins, absolutely no virus babies. So this entire process in which several enzymes help RNA to disrupt or interfere itself is called RNA interference. So I will write this down, possibly in a different color. So this is RNA interference or in short we call it RNA small i. So this entire process is called RNA interference and all of these components of this process have their own names as well. For example, when Dyser chops off this longer double-stranded RNA, then it gives these really smaller pieces of RNA, right? Then these are called literally small interfering RNA or SI RNA. So I couldn't write the whole thing because I don't have space. So let's write it somewhere else. Let's move this a little bit here. So SI, wait, both needs to be small, so this can't be capital. So SI RNA, this stands for small interfering, interfering, I need more space, clearly, interfering RNA. This is the same RNA that has the neon stickers attached to it, the same stickers which will be recognized by this yellow blob of a complex. And this complex, it also has a name of its own. It's called RISC and if we expand that then it comes to RNA-induced silencing complex. Now why silencing complex? Why are we calling it a silencing complex? So essentially when we are stopping this mRNA from translating into its proteins, we are actually stopping a gene from expressing itself. So in a way, we are silencing the gene. So which is why this entire process of RNA interference or RNAi is also called gene silencing or gene knockdown. So this entire process is also called gene silencing or knockdown. But RNA interference doesn't just protect you or defend you from these outside threats, like viral RNAs. It also protects you from inside threats. And one of these threats, they come in the form of something called micro RNA. So I'll write it down here. It's called micro RNA or in short we call it small m, small i, mi RNA. So these micro RNAs have been long associated with the development of various types of cancer. If we don't get rid of them, we might succumb to cancer more often. Thankfully RNA interference can also play a part and get rid of these micro RNAs as well. So how does that happen? So one of the things about micro RNA, again, let's zoom in. Okay, so this over here that you can see this hair pin like structure over here, this is the micro RNA. So we'll just write it down. This is the micro RNA. Now when, so the thing about a micro RNA is that it's actually a single stranded RNA sequence. But what it does, it folds back on itself and with the help of this forming this hair pin like loop structure. And it forms a structure, something similar to this. So it also has a sense and an antisense strand, although it started out as a single stranded RNA sequence. Now when this happens, then dice are what it's going to do. It's going to come over here and chop off this hair pin structure right from the middle. So this hair pin structure, it will chop it off like this. Then what is remaining from this is this double stranded MI RNA. This is also an MI RNA. And this looks very similar to this small interfering RNA from that viral RNA cycle that or the process that we saw this one. So these two are very similar to one another. They both have two strands and they both have the same number of base pairs. So they're pretty look pretty similar looking. So again, the entire process now flows as it goes on for our viral RNA process. Again, risk shows up and it's going to bind to this MI RNA sequence, the micro RNA sequence. And then it's going to split this into two strands, the sense and the antisense strand once again. And it will get rid of the antisense strand and it will keep only the antisense strand and it's going to look for its complementary mRNA and find that and then slicers are going to show up and cut off this mRNA. No mRNA, no proteins. So RNA interference is very specific that way. Like it will follow a very specific path and it will kind of stick to that and which is exactly what happens here. It is so precise. It has this one pathway to follow. It will only chop off those complementary mRNAs that binds with this antisense strand and it sticks to that. It doesn't really deviate much, which is why RNA interference or this entire process has become a breakthrough in the medical field, not just medical field but in biology in general. So and its applications, there are so many applications of RNA interference that we would actually need another whole video to just talk about them.