Ask A Scientist© Molecular Biology Archive

>
> > >   name        Jim
> > >   status      student
> > >   age         15
>
> > >   Question -  On a radio program that I heard last
> > night, the guy said
> > > that one gram of DNA has the ability to store as
> > much information as 1
> > > trillion CDs. is this true. Also stated in this
> > program, was that if
> > > there was a strand of DNA the size of a pin head,
> > and you wrote down all
> > > of the information into a book, that book would be
> > 500 times the distance
> > > from the earth to the moon big. Both of these
> > statements sound rather far
> > > fetched. So what I'm looking for is if this
> > information was factual or fiction?
> >
>Is this fact or fiction? Or is it neither? You are
>comparing different quantities and qualities. DNA is a
>chemical molecule of a particular size, and you can
>measure it's length. DNA is a chain consisting of 4
>bases, that build a double-stranded molecule.  A
>stretch of 3000 basepairs (two antiparallel strands of
>3000 bases each) would be 1 micrometer long (1/1000
>mm). So you can calculate how many basepairs were
>needed for a km, and extrapolate that to the distance
>moon-earth.
>
>DNA has a mass, and from the molecular mass of the
>bases you could calculate a weight, however for DNA to
>be biologically functional it needs to be wrapped
>around protein, so the mass of a functional chromosome
>is more than that of the DNA only. The same accounts
>for the volume DNA occupies. Would this 'pin head' be
>the volume DNA occupies in the cell, or a
>chrystallized form?
>
>We use letters as symbols for the bases, as a
>short-hand notation. That is completely arbitrarily.
>We could have called the bases by their names (guanine
>for G, cytidine for C, etc.) or given them different
>names, or use their molecular structures instead, and
>that would increase the size of representing a DNA
>stretch on paper with a factor 10 or more.
>
>But what does this mean in terms of information? A
>book consists of letters, and these letters form
>words, then sentences, then pages.  A word in a book
>can be 1, 2 or 20 letters, a sentence consist of 3 or
>30 words, a book of 10 or 1000 pages. How much do you
>need to read before you identify a book? When I quote
>'In the beginning...' you probably recognize this as
>the bible, but 'Once upon a time...' could be any
>fairytale. You can only leave out a few words without
>changing the meaning of a sentence, and you would not
>accept a print of a book with pages missing.
>
>In analogy the information carried by DNA is stored in
>genes. You may need 300 bases for a short gene in a
>bacterium, or 300 000 bases for a gene in a eukaryote
>(also counting the interrupting sequences that we call
>introns). Some properties are stored in one gene only,
>but more often you need many genes for a certain
>characteristic. There may be 20 genes needed for
>bacteria to survive a midsummer day (heat stress), 200
>genes for cell division, 2000 genes for human
>behaviour. Every organism has a surplus of DNA, and
>could survive when parts were missing, to a certain
>limit. However most is essential to that particular
>organism, otherwise it wouldn't be there.
>
>How would you convert such 'information' into the
>quantity 'size' (distance moon-earth) or 'bits' (cd's)
>or 'volume' or 'weight'? The codes that we use for the
>bases, and thus for the genes, bear no correlation to
>the amount of information stored. A long gene is not
>'smarter'. The amount of DNA is not even a measure for
>amount of information stored. Simple organisms can
>contain more DNA than more complex organisms.
>Information has no unit.
>
>Trudy Wassenaar
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>It's hard to know if that is true or not. I'm sure that its based on
>mathematic calculations.  Remember that we are dealing with molecules which
>are too small to see. Every cell in your body (except red blood cells)
>contain all the genetic information necessary to make you.  The DNA is
>supercoiled and packed into each cell.  If you took one gram of cells (which
>would be ALOT of cells) each having their complement of DNA that would be
>ALOT ALOT of DNA.   So although I don't know the exact amount, mathematically
>it must be ALOT!!!
>
>vanhoeck

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