HIV

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NaziaC
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HIV

Unread post by NaziaC » Thu Dec 16, 2010 6:50 am

কালকে আমার Intro bio exam পড়তে গিয়ে একটা interesting question পাইলাম-
Some individuals are resistant to HIV infection even after repeated exposure. Assuming that these individuals express a normal level of CD4 receptors, how can you explain their resistance to HIV?
NB: CD 4 is the receptor necessary for the docking of the virus with the cell.
have fun thinking about it. =)
"Be less curious about people and more curious about ideas."

NaziaC
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Re: HIV

Unread post by NaziaC » Mon Jan 17, 2011 8:46 pm

What's up, guys?
Do you want some hints? Here you go!
1. How does HIV enter your cell & which cells do they specifically attack?
=> Very simply speaking, HIV has 2 glycoproteins on its envelope gp41 & gp120. These glycoproteins bind to proteins called CD4 & MHC class 1 & 2 (like plug-pins bind to sockets). These specific proteins are available on the surface of a specific class of cells in our immune system called the T-helper cells. So HIV always attacks only the T-helper cells.

2. What does HIV do after entering the cell?
=> HIV is an RNA virus. What it does is it makes a DNA strand using its RNA as a template and an enzyme called reverse-transcriptase. Then it goes on making the second strand of DNA. After a while it has made a double-stranded DNA from its RNA, right? Then HIV uses another enzyme called integrase to incorporate its own genome into human-genome. SO NOW THE AFFECTED PERSON IS CARRYING THE HIV GENOME WITH HIM.

3. How does the genome work while inside your body?
=> So HIV is a very cunning virus. It does not start replicating as soon as it is incorporated in human genome. It sits there idle even for 10 years in some case. So when the person gets affected by some other disease, his T-helper cells begin to multiply to fight against the second disease. With that proliferation, the HIV genome gets activated & starts to express the HIV proteins. Only then the person starts to express the symptoms.

In case of this question 1 & 3 do not work. Because the question says the receptors work perfectly. So the answer is hidden in point 2, maybe? Think!

The process I described here is as simply explained as possible. The actual thing is more complex & has a lot of questions involved. If you have more questions, I'd love to think about them!
"Be less curious about people and more curious about ideas."

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Abhijeet Dutta
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Re: HIV

Unread post by Abhijeet Dutta » Sat Jan 29, 2011 11:05 pm

I must say you explained well with having the simpler interpretation in mind :D
I actually have a question that I asked to my teacher and He advised me to ask a "Virologist"
I hope you're gonna help.
"As far as I have known about HIV's history, I read that it came from a monkey type specie to a human.
I don't know if its true or not. It stays in blood as T-lymphosite cell is in WBC. So from monkey how it came to Human Body??(Don't want to imagine that our Human had tasted the roost of a monkey!! That's just a history I knew But as Genome is the thing that is what helps it to work or survive I'm having an assumption about the genetic linkage! It may lead to the evolution hypothesis given by Darwin.Well that's what I felt, not a biological guy but just assuming. Your explanation will be great to clear the point. )
I have read that "Flu" viruses have got an unique property to change their outlook each time they attack Human body so our body actually can't detect the enemy though it has the antibody ready for its diminishing(As I told you I'm just a hither thither leaner in Biology so if you would be kind to explain with a touch detail as I've got somewhat enthusiasm also)
Just got a info that HIV can also mutate making the immune system puzzled to figure it out.
Do this have any connections??
And your questions' answer might be
"Probably the production of viruses depends largely on its decoding in the genome of human body.
So if a persons' body is made to undecode the Genome of any thing like HIV then he can show some resistance against it."
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NaziaC
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Re: HIV

Unread post by NaziaC » Sun Jan 30, 2011 5:45 am

Hehehe!!! Don't worry! Humans didn't necessarily taste the roost of a monkey!
What it means is that probably the primitive gene in HIV mutated into a pathologically active gene(one that causes AIDS) in monkeys' body for the first time. & the mutated HIV virus entered human body through food/air/water & began its work.
Your question about the mutation part is really interesting.
So there's an enzyme called Polymerase that nucleic acids (DNA & RNA) use to replicate & amplify. So normally, for example, in our body, each time one cell divides a daughter DNA strand is made from the mother DNA using DNA dependent DNA polymerase. This polymerase enzyme has a proof-reading activity called 3'to 5' exonuclease activity. Suppose, your mother DNA has the base T in one place. Your replication machinery, by mistake, copied a C instead of T (Yes, It does commit mistakes). Then the proof-reading quality of the DNA dependent DNA polymerase will allow it to refine the mistake. So this kind of polymerisation has little chance of mutation.
But in case of a retro-virus (http://en.wikipedia.org/wiki/Retrovirus), like HIV & some flu strains, it is making a DNA using its RNA as a template. Then it's using another type of Polymerase called RNA dependent DNA polymerase. Unfortunately, this type of polymerase does not have a proof-reading quality. So the replication machineries very often copy the wrong bases & mutations occur more frequently. As I said, HIV is a cunning virus. For its survival it uses this weak-point of the RNA dependent DNA polymerase & adds frequent mutations in its genome. Our immune system does not recognise the mutated form of HIV & that's why it is so hard to fight it off.
Does that make any sense?
Good job! You did it!
Now here goes my answer:
Yes, the problem( or should I say a blessing?) is that those people do not have integrase in their cells. So the HIV genome fails to incorporate into human genome & replicate. So they have a good resistance against HIV.
"Be less curious about people and more curious about ideas."

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Abhijeet Dutta
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Re: HIV

Unread post by Abhijeet Dutta » Sun Jan 30, 2011 10:45 pm

You did well and I tried hard to capture the points but as you don't know I'm general student of biology but a full geek to Physics so this kind of biological things have wrecked my brain to somewhat extent(Matha Gurachche!!!)
But ur writing was good enough though link was a tough one.
HIV uses our own system against us by inserting the provirus into our genome that carries the viral info and gradually build the total DNA of HIV in our cell and once one is being made it then starts to effect other cells and process goes on ..................(dot kom pore jabe!!)

Your link also helped me a lot .
I'm wanting to know if the mistake making habit of replicationary system is pretty fluent and why it actually make the mistakes(I may be getting into technical mechanisms but it will be again great if you clarify it.)”
And your quote, "the mutated HIV virus entered human body through food/air/water & began its work."
If that happened then I'm scared!!!(Ore Baba re!!)
Please just add more info there because as u got the point, it seems like food/air is not safe so how can I take any step against it besides u know the society has got a bad concept about it.
And thirdly, the mutation of genes there is just the permutation and combination of nitrogen base(If I'm not wrong)
So if there is any link to the "Evolution" Hypothesis that I asked before but couldn't get your point clearly there(Its your fault!! You write so well that sometimes if one or two points are not precisely described seems like not described at all !!!)
And with that portion I wanna probe(too much asking actually!!) if our Genetical Guys know precisely about this game of Permutation and Combination and if they can assume how life evolved both of virus and simple life + how it can change in future with surprisingly newer speices.
If u want can answer one by one as I asked many things(which I think need some writing to do) that requires you beauty of well explanation.
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NaziaC
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Re: HIV

Unread post by NaziaC » Mon Jan 31, 2011 4:00 am

No, what I meant is that the primitive from of the virus might have entered human body through air/water/food/ even blood. The present HIV that causes AIDS is transmitted by some body fluids, surely.
I haven't studied evolution that much. So I'm sorry I can't tell you about that. Is Saumitra bhai in this group? He might have answers.
The mistake is not VERY frequent. I forgot the exact number, but it's one base in some millions. Making mistakes is the characteristic of every single entity in this world & our body is not an exception. :)
"Be less curious about people and more curious about ideas."

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Abhijeet Dutta
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Re: HIV

Unread post by Abhijeet Dutta » Mon Jan 31, 2011 10:28 am

Thanks for the answers.I asked too much but none the less I got some useful ideas now.
:)
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miTTTir
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Re: HIV

Unread post by miTTTir » Fri Feb 25, 2011 11:20 am

First of all, evolution is not a hypothesis, it is a statistical fact according 'modern Darwinian synthesis'. But there are certain applied areas to explain things based on evolution, are regarded as 'evolutionary hypothesis'.
According to the best documented historical evidence and supported by recent genetic studies, the 'black death' or the Plague epidemic exerted a strong 'selection pressure' over the human population of Europe for 150 years till 19th century causing half of its population to die out, thus bringing about a major shift in their 'gene pool'. The lucky guys who survived the Plagues had mutations beneficial for them to fight the disease off naturally. And resistance to HIV is thought to be a by-product of those mutations.
There are a lot of terms in 'quotes' above those have very precise technical definitions. But It'd be exhausting for me to explain them all here! And yes, 'how did HIV evolved as we know it?' - is a completely different question, which we will discuss later, maybe.

miTTTir
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Re: HIV

Unread post by miTTTir » Fri Feb 25, 2011 11:32 am

HIV has evolved from SIV which is a virus that infects apes. In sub-Saharan Africa, people use to eat monkeys and often gets SIV in this process. SIV is not harmful for human. It was just a matter of time for SIV already present in human body to evolve into something else that could survive and propagate in humans or get into oblivion, both chances being likely enough. Yes, close evolutionary relationship between apes and humans have aided in the evolution of SIV to HIV, because it needed only a few amino acids to change in viral surface proteins due to close similarity of ape and human immune system.

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