When flu viruses attack! Learn how flu viruses get into and out of your cells using Hemagglutinin and Neuraminidase proteins on their surface. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.
When flu viruses attack!
- Let's talk about exactly how flu causes so much damage
- to ourselves and why it makes us feel
- so lousy whenever we get the flu.
- And I start up with drawing the flu virus here.
- This is our influenza virus,INFLUENZA VIRUS.
- And we have on influenza a couple of features
- that we have to remember.
- So you know, on the out side there is a sort of envelope.
- And what's on the inside of this envelope
- are 8 bits of RNA, 8 pieces of RNA.
- And so this RNA is important to remember
- because in the human cell in our cells, I'm going to draw one of our cells right here,
- we have instead of RNA we have DNA, remember.
- And so this is our nucleus.
- And on the inside of the nucleus is our DNA.
- So this is our DNA over here.
- So the virus has RNA and we have DNA.
- In the outside of the human cell, I should have been labelling this over here, this is HUMAN CELL.
- The outside of the human cell has something called
- SIALIC ACID
- There are these little strings over here. They are coming of
- and I'm drawing them far larger than they are in real life.
- They're not nearly this big.
- But there are these little, tiny little things called sialic acid.
- And this sialic acid becomes very important in understanding how the influenza virus
- gets into and out of our cells
- So the outside, remember, of the influenza virus there were couple of proteins
- And I'm gonna draw one of these proteins here.
- I'm gonna make it look like a hand.
- So this is a little hand and this protein is called HEMAGGLUTININ
- In fact previously I called the H protein and you can call that if you want.
- But the full name is hemagglutenin.
- And what hemagglutenin does is that it actually holds onto sialic acid.
- In fact that's an easy way to remember, right, because H and H go together
- It holds sialic acid.
- That becomes very important because that allows it the first step towards getting into the cell
- That is another protein on the outside here.
- I'm gonna make it look like a pair of scissors.
- Because it will kind of remind us what this one does.
- And this is called neurominidase.This one is called neurominidase.
- And I'm gonna pass on explaining what it does just for the moment.
- I'll tell you a little bit what it does.
- So then the first step to get into the cell is for hemagglutinin to hold on sialic acid.
- And than there are few other small molecular steps that happen,
- important ones but I'm gonna suffice to say gets inside.
- And once the influenza virus gets inside,
- these are RNA segments they're let loose.
- So these segments are gonna start making their way towards the nucleus.
- So once they get into the nucleus they are in the same kind of area that DNA is.
- And what they do is remarkable.
- They basically take over.
- These little RNA start making many copies of themselves.
- And what they want to do is make our human cell into a factory.
- They want to make a factory and this factory is gonna make little proteins, viroproteins.
- And it's gonna make viral RNA.
- And what it's not gonna do the one thing that cell is no longer gonna to be very good at doing
- is its normal job.
- So the human cell of course had some job to do
- and it's not gonna have the resources or the time to do it
- because it's basically been taken over by this viral RNA.
- So what happens then is that the viral RNA is basically turned into a factory and
- what it wants to do is make more and more copies of it selves.
- Let me just show you what that would look like.
- Here is a daughter cell, lets say it goes over here.
- And I'm gonna clean this up a little bit, just to make sure that we're looking at a nice and neat picture.
- Let's say something like this.
- So this is our daughter cell on the other side.
- And these cells are gonna try to make their way out of the human cell, right?
- Because now they're a package, they are ready to go.
- And where these suppose they wanna go next?
- Where they gonna wanna find their own human cell to invade.
- Because they wanna to continue this process.
- We've got more human cells over here down below.
- We've got maybe let's say one human cell up here.
- So we've got new targets for this virus.
- And this virus is going to seek out these targets and try to make its way inside
- again using its hemagglutinin.
- But before it can do that it's gotta break loose, right?
- Because it's still attached to that sialic acid.
- It's here where neurominidase comes in.
- And neurominidase it basically, it nicks.
- And there is with the N is helpful for remembering it.
- It nicks or cuts sialic acid.
- It's if a nicker cut that sialic acid it can break free.
- As I remember the two proteins as hemagglutinin holds sialic acid to enter the cell
- that is on entry and the neuraminidase is gonna nick the sialic acid
- and that important for exiting the cell.
- But we still haven't answered the question : how does all this cause our symptoms?
- or what happens is as these cells get turned into factories
- they start dying or getting damaged.
- And all their content start leaking out.
- So all these contents from the cell start leaking out and as they do they create inflammation.
- Let me bring a little bit up the canvas.
- If you have an inflammation, let's say that inflammation is happening in your nose
- well you might say : well I have a runny nose or a stuffy nose.
- Or if that inflammation is happening in your throat you might say: well I have a sore throat, might hurt.
- And if it's happening in your lungs you might have a cough.
- So one of those respiratory symptoms, remember that we've got two categories,
- All other respiratory symptoms, I'm gonna shorten it as RESP.
- Those are gonna be explained by inflammation or at least a part of inflammation.
- And remember there are also constitutional symptoms, right?
- With constitutional symptoms, those were things like having a fever or having fatigue.
- And the reason for that is that your immune system is going wild and crazy
- when you have influenza.
- It's gonna be attracted to all of those chemicals, we call these cytokines that were being released .
- And it's gonna to be attracted to the fact that you've got actual virus particles in the area,
- you know that is being infected.
- So that strong immune system is going to create some of your symptoms.
- It's actually gonna rave up your temperature.
- You'll start having a fever, chills.
- And because your energy is spent on this attack
- you're going to be fatigued.
- you're going to be fighting off the virus so you going to be fatigued,
- you might have the body aches.
- So lot of these kinds of symptoms you get as result of a strong immune response.
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