<< I asked a similar question the other day, but no answers yet so I'll
repeat it here: How can it be known that this DNA "is not used by
organisms"? Is current understanding of genetics really that good?
>>
The short answer, No. Like most of science, it humbles.
Of course with the human genome for one set of genes is
nearly finished --- although Celera is actually not "finished"
exactly. So in principle, we know where the genes "are".
However, that doesn't mean we really understand what the
space between them is doing.
For example, DNA folds into chromosomes. How does it
do that. Well, we have theories about twisting (like a when
you roll a rubber band,it folds), but how does that produce a
specific *global* fold of a chromosome? err..... This is the
majority of the "junk" in our genome. I forget the exact
percentage but something like the better part of 95 %.
There is not that much stuff that "codes".
There are also introns. Some people also called this
"junk" not so long ago. Actually, cell differentiation
(making a brain cell instead of a liver cell, etc.) is dependent
on that "junk" to make it happen. This is the result of what
they call "alternative splicing". When messenger RNA is first
constructed (in the nucleus), it has exons (the coding
information for proteins) and introns (non coding "junk"
inserts). The introns are spliced out, and this early form
of RNA is modified with a vast array of proteins in to a
"mature" messenger RNA while is shuttled out to the
cytosol (the area outside the nucleus) where it is used
to make a protein.
When the introns are spliced out in an alternative splicing
process, different coding sequences are created depending
on how the vast array of proteins signal these introns.
How does it work? errr.....
There are some explanations, but the point is that we really
don't understand that much about the system as a whole.
Isolated parts, extrapolations, but there is a long long way
to go.
by Grace alone do we proceed,
Wayne
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