Forget your Hans Grubers, Lord Voldemorts, and Jean-Baptiste Emanuel Zorg — it’s
time to meet some real supervillains.
Well, supervillains as far as the human body is concerned.
They’re called retroviruses, and they actually change their host cell’s DNA.
You’re probably familiar with viruses: they’re super small — roughly a thousand times smaller
than most bacteria, which themselves are much smaller than most of the cells in your
These microbes are essentially a floating protein shell with a little bit of DNA or
RNA inside, which are the molecules they use to store their genetic information.
The virus only attaches to certain types of cells, depending on the type of virus.
Once it finds the cell it needs and latches on, the virus releases its guts into the cell,
where it then uses the machinery of the cell it’s infected to make more viruses.
细胞中的制造工厂 核糖体 会读取病毒的RNA
Ribosomes in the cell, which are basically the cellular manufacturers, read the viral
RNA and start making the amino acids the RNA says to make.
Those amino acids become enzymes, which create protein shells and more viral DNA and RNA,
which then come together to form more viruses.
The new viruses pile up until they explode out of the cell, releasing more viruses into
Viruses can use this process to spread really fast.
幸运的是 在它们吞没一切之前 我们能制造出
Luckily for us, we can create antibodies to recognize and destroy cells infected with
viruses before they overwhelm everything.
Still, even regular viruses can be pretty dangerous to the health of a cell.
But, retroviruses make regular viruses look like a bunch of dumb babies.
Retroviruses get their supervillain status because of an enzyme called reverse transcriptase.
Reverse transcriptase reads the virus’s RNA and turns it into DNA, which then makes
its way into the cell’s DNA and attaches itself.
Once the viral DNA is in the cell’s DNA, the cell just starts copying the new DNA along
with its own.
After the retroviral DNA infects a cell, it can lie dormant for a while before it activates
On top of this these viruses are reproduced a ton, so it provides lots of opportunities
All of this makes it incredibly difficult for the immune system to fight them off.
Let’s take a look at a real-world example: HIV.
HIV targets a certain kind of immune cell in the human body called CD4.
These cells are also known as helper T cells.
After breaking into the cell, HIV’s RNA and reverse transcriptase enzymes start creating
lines of HIV DNA.
That DNA makes its way into the CD4 cell’s nucleus, and sews itself into the cell’s
Now that it’s part of the cell’s genetic makeup, it can start wreaking havoc.
Sometimes it can cause damage almost immediately.
Othertimes, it can stay dormant for years while it’s reproduced all around the infected
host’s immune system.
The virus eventually disables the cells that it infects, or sometimes even kills them.
Having a compromised immune system exposes the human body to all sorts of different dangers,
and HIV eventually progresses into AIDS, a serious and often fatal condition.
Fortunately, there are treatments for retroviruses.
In the case of HIV, the patient’s usually given a cocktail of drugs to fight the spread
of the virus.
These drugs usually do one of two things: prevent reverse transcriptase from becoming
active, or stop HIV from entering the cell.
But they can’t cure HIV — they can only slow it down.
Even though they’re so hard to fight, retroviruses might have helped shape human evolution — and
we might even be able to use them to /fight/ disease.
By analyzing the human genome and comparing it to what we know about retroviral genomes,
researchers estimate that somewhere between 1 and 8 percent of the human genome came from
These viruses infected our ancestors millions of years ago, and the changes they made to
their DNA stuck around.
These days, most of those virus genes have mutated to the point where they’re totally
inactive and don’t really affect our lives at all.
But a few have been linked to diseases, especially autoimmune diseases and some cancers.
Hopefully, learning more about those links will help researchers develop new treatments.
And some researchers are looking into how to use retroviruses /themselves/ as treatments.
Since retroviruses can change a cell’s DNA, they can be used to insert new genes to fight
diseases, like certain cancers.
There have been some problems with these treatments, though, since retroviruses can be kind of
unpredictable when it comes to changing a cell’s genome.
For example, they might insert the new gene right in the middle of another gene, which
could interfere with important processes in the cell.
But researchers are looking into ways to make retroviruses insert new genes only in very
So the ability that makes retroviruses so dangerous might also eventually make them
a powerful treatment.
Thanks for watching this episode of SciShow, which was brought to you by our patrons on
If you want to help support this show, just go to patreon.com/scishow.
And don’t forget to go to youtube.com/scishow