Understanding RNA Interference: Mechanisms and Applications

in today's video we're going to talk about an amazing molecular biology concept called RNA interference or RNA I

where this I stands for interference now what is this RNA interference and where is it used to understand what is RNA

interference let's first look at the mechanism of gene expression so in the gene expression mechanism we start with

DNA which is transcribed the genes in the DNA are transcribed to give mRNA and the MRNA is translated to give proteins

and the proteins carry out all the cellular functions needed for life so where does this RNA interference come in

this gene expression well this is a mechanism of regulating this gene expression so by regulating we mean that

the protein production is going to somehow be stopped no proteins will be produced by this mechanism of RNA

interference because it is interfering in this process specifically where the MRNA is being translated into proteins

right it is interfering in this process now what carries out RNA interference RNA interference is carried out by

double stranded RNA yeah you heard me right not double stranded DNA but it is double stranded RNA double

stranded RNA generally doesn't occur in cells naturally it occurs as genetic material for some viruses it is not

normally found in cells but it can be produced inside our cells under special circumstances we'll talk about that

later when we talk more about RNA interference so what are the types of double standard RNA that can trigger

this RNA interference mechanism there are two types of double strandard RNA that can trigger RNA I they are small

interfering RNA or Si RNA and micro RNA or M RNA keep care while writing SI RNA because SI should be in small letters

and RNA should be in capital letters similarly while writing micro RNA Mi should be in small letters and RNA

should be in capital letters also don't get confused between micro RNA and M RNA M RNA stands for micr RNA and mRNA is

the gene transcript that we get after transcription so how are these dsrnas involved in regulating the gene

expression first we'll start with small interfering RNA one thing to know about small interfering RNA is that they're

usually found when there is a viral infection when a double standard RNA virus infects a host then the host's RNA

interference mechanism is kicked off that is what produces this small interfering RNA this has a lot of

potential uses I mean the SI rnas can be cloned and artificially expressed it has a lot of potential uses we'll talk more

about that in further videos so because they don't naturally occur in our cells SI rnas are exogenous in contrast M RNA

or microrna may be produced within our cells under special circumstances which makes them endogenous so first we'll

talk about the SI RNA and how it is formed so here we have a host cell which is now being invaded by a double

standard RNA virus now this virus is going to inject its genome into the host cell which is this double standard viral

RNA and this is going to hijack the host cells Machinery to produce viral proteins which is exactly what we want

to avoid because those viral proteins would then be involved in producing more viruses and in causing infection so how

does Si RNA prevent that from happening so we're going to focus only on the double strandard RNA that is now inside

the cell from the virus because it's not usually found in the cell this unusual RNA a is recognized by a protein known

as daiser keep care when you're writing this name daiser this D should always be Capital so this daiser protein is going

to come and recognize this double standard RNA now what this dacer like the name suggest is going to do is it's

going to chop this double standard RNA into smaller pieces that's very important for the formation of Si RNA

because the SI RNA is nothing but these small chopped bits of double standard RNA so once daer comes in contact with

this double standard RNA it's going to chop this long strand of RNA into smaller bits which are known as small

interfering rnas now you have to remember that the RNA is going to have opposite polarity like DNA right because

it is double standard one is going to run from five Prime to three prime the other is going to run from three prime

to five Prime now when daer is chopping this up it's going to add certain tags here certain molecular tags that can be

recognized by a complex of proteins not just one protein it's a complex of many protein subunits that's going to come

and bind to this double standard SI Arin now one such protein that is part of this complex is known as Argonaut and

when this complex of proteins binds to this SI RNA it forms something known as RNA induced silencing complex or risk

and it is this risk that's going to trigger the interference mechanism it is going to make sure that translation of

mRNA does not occur now which mRNA are we specifically talking about we're going to talk about the viral mRNA

that's going to produce viral proteins right so once this risk is formed one strand of this double standard SI RNA

this is going to get degraded this is known as the sense strand only the other strand which is known as The anti-sense

Strand will remain now why is this important you see this anti-sense strand has sequences complementary to this

viral mRNA let's say the sequence here is a u because this is RNA do DNA g c so there's going to be a bit of RNA here

that's going to have a complimentary sequence to this sequence this is going to be u a c g now what is going to

happen is that this risk complex this is going to come and bind to this specific part of this viral mRNA and that is

going to activate this Argonaut protein which is also known as slicer and like the name suggests this slicer is going

to slice this viral mRNA into little pieces like it's going to chalk the MRNA into little bits now with the MRNA now

chopped into pieces translation cannot occur the viral proteins cannot be produced by means of translation this is

the entire goal of this RNA interference mechanism so this small interfering RNA is going to become part of this RNA

induced silencing complex risk the sense strand is going to be degraded The antisense Strand containing risk now is

going to come and bind to one part of viral mRNA and then slicer which is Argonaut is going to chop this viral

mRNA into pieces making sure that translation does not occur now one thing you have to remember is this s RNA is

highly specific to specific mrnas these s rnas have Target sequences that will bind to only specific mrnas and not any

other mRNA that is in the cell now that we've learned about sna let's move on to Mna and how it performs RNA interference

so I told you earlier that Mna is endogenous right which means that it is produced within our cells as well now

where it is produced is first it is produced in the nucleus from DNA specific parts of DNA that don't code

for any protein so this is non-coding RNA so from DNA a non-coding single

strandard RNA is produced by transcription now certain proteins within the nucleus like drosa this is

going to convert the single standard RNA into a double standard RNA by folding it upon itself so this RNA strand is going

to fold upon itself forming a hair pin Loop like structure that then makes it a double standard RNA these base pairs are

actually now complimentary if this is a this is u if this is G this is C like that then

this double standard RNA now this is the micro RNA this is going to be move to the cytoplasm in the cytoplasm it will

encounter dicer this dicer what it's going to do is it's going to chop this hair pin Loop here it's going to chop

this part of this Mi RNA so we're going to be left with just a double standard RNA sequence that has one sense Strand

and another anti- sense Strand and now the process is similar to the sna process and the risk complex containing

that Argonaut protein is going to come and bind to this double standard Mna after which the sense strand is going to

be degraded and now this complex risk complex this can Target mrnas in two methods one way is like how the sna

worked it can go and chop the MRNA by binding to this target mRNA specific sequences like say this is G CC this is

is going to contain c g g this is going to come and bind to this and slicer again which is Argonaut this is going to

chop the Mna into bits and pieces so no translation will occur another method by which Mna can prevent the expression of

this target mRNA is by targeting its three prime utr or the three prime untranslated region now this three prime

utr is a region located near the three prime end of the MRNA that acts as a transl ation termination sequence so it

tells the translation process that you've reached the end of the MRNA there is no more mRNA to be translated so what

this Mna does is that it goes and binds to this three prime utr region of the target mRNA by doing so it's going to

prevent the translation of the protein now this is very useful because this way Mna becomes highly nonspecific towards

the Target mRNA it can Target a wide range of mrnas by binding to the three prime utr region This is highly useful

because now the mrnas can be used to prevent the translation of mrnas that can lead to proteins that cause cancer

so these mrnas have been formed from mutated onco genes or DNA repair genes and now if proteins are produced from

this mRNA it's not going to be able to regulate the cell cycle and cell division or contact inhibition so those

proteins that can lead to cancer can be prevented from being produced when the Mna binds to the three prime utr region

of those Target mrnas now this is highly useful in the field of genetic engineering as well because the m rnas

and the S rnas can be used in the field of Agriculture to produce pest resistant plants we'll take a look at how this RNA

interference mechanism is used to produce pest and plans in another video