RNA seems to have
a big role in regulating gene expression and
so do many of these non-coding regions. We
are going to take a deeper look into transposable
elements or transpose on some jumping genes
because I think they are particularly interesting.
Very very lively area of research at the moment.
If we look at this Pi chart, you can see that
there are a lot of different sorts of transposons.
Some of them are dead. We will look at those
in a little more detail. We have some long
terminal repeats those, towards the ends of chromosomes.
We have some short interspersed elements.
We have got more and more acronyms here, science
and lines and we have lines long interspersed
elements and then we have the rest of the
DNA. Over 45 percent of our genome is made
up of transposable elements or jumping genes.
So tell me they don't have some sort of role
and we are finding out that they really do.
The rest of the genome with non-coding and
coding DNA that is 55 percent. So a lot of our
genome has to do with these transposable elements.
Let us take a little bit of a closer look at what
some of them do. LINES are long interspersed
elements. They are long. They are about 6000
base pairs. They can price about 21 percent
of the human genome. That is kind of a lot.
They have their own machinery that allows
them to transpose themselves. Basically, they
can cut themselves out of the genome and they
can copy themselves and insert themselves
into another genome. They contain genes that
code for proteins that allow them to do all
of these themselves. It is pretty cool.
That is when I first started realizing they must
be up to something. They have a purpose if
they have all those types of machinery. We
might see retrotransposons. A lot of transposons
are retrotransposons. That don't mean they
are really old, but it means more that they
are able to make a copy of themselves. We
have transcription. We make mRNA and that
mRNA if they have a gene for reversed transcriptase
can then be reversed transcribed back into
DNA so that they can put that transposable
element somewhere else in the genome. Literally
these genes do jump around all over the genome.
Pretty exciting I think.
Inside of LINEs sometimes we find SINES, short
interspersed elements. They are shorter and
they utilized the machinery of the LINEs, the
long interspersed elements. They are often
embedded inside long interspersed elements
to use their machinery.
Again LINE involved genes that code for
the machinery or the enzymes or proteins involved
in transcription and translation of themselves
and the endonucleases that might cut DNA and
allow them to pop back into a sequence somewhere
else. Often signs are seen to interrupt genes.
Let us say theoretically, we didn't want this
particular gene expressed a sign may come
jumping in there and jump into that gene and
stop it from making any sense. It is interrupting
the genes so when that gene or that gene would
not be transcribed into a successful mRNA
or translated into a successful protein. SINEs
embedded in LINEs often involved in interrupting
in other genes. Then we have long terminal repeats.
repeats also code for the round reverse transcriptase
so that they can transcribe themselves from
messenger RNA making a DNA copy that they
can stuff back into the genome some where else.
Very exciting stuff with all of these different
transposable elements because they all seem
to be having some sort of impact on gene expression
and moving junks of DNA around, again a huge
area of research presently. So the final piece are
these dead transposons. It seems
like dead transposons are transposons that no longer have
the machinery associated with them to transpose
themselves. We really don't have a clear understanding of
what that transposons do or if they are simply
dead or do they have some other kind of role.
The long and the short of it is, there is
a lot of material that is not coding DNA that
probably impacts how DNA is actually expressed.
That could account for why we have much less
coding gene than we have thought we might
have when we were initially sequencing the
genome. Our complexity could come around because
of all of these different pieces of DNA particularly
transposons and RNA coding sections that might
regulate gene expression.