Biology Reference
In-Depth Information
if we assume that each of the 10 positions in the 10-nucleotide message can be
occupied by any one of the six nucleotides, A, C, G, T, A
0
and T
0
, where A
0
and T
0
are covalently modified nucleotides. Hence the Hartley information content of the
message would be log
2
(6
10
)
¼
10 log
2
6
¼
10
2.6
¼
26 bits. That is, if the
¼
above decanucleotide (deca
10) is chosen out of all possible decanucleotides
formed from the six elements, A, C, G, T, A
0
and T
0
, then the amount of information
that can be carried by the decanucleotide (or by any one of the rest of the set,
including, say, TTTTTTTTTT or AAAAAAAAA) is 26 bits. Because Hartley
information or Shannon information cannot distinguish between individual
messages, they are unable to convey any meaning of a message.
Turvey and Kugler (1984) made the interesting suggestion that there are two
kinds of information - (1) the orthodox information (also called the
indicational/
injunctional information
), often associated with symbol strings, that
indicates
and
instructs
(e.g., stop signs, genes), and (2) the “Gibsonian” information (also called
the
specificational information
), not expressible in terms of symbol strings that
provides
specifications
(e.g., visual information from surrounds guiding a driver to
stop at a desired location at a desired time). “Information” is akin to “compounds”
in chemistry. Although all compounds are made out of one or more of the slightly
more than 100 elements in the periodic table, the kinds of compounds found on this
planet alone is astronomically large (10
9
-10
12
?), and chemists have come up with
rational methods for denoting and classifying them. It is clear that the number of
the kinds of information that we can conceive of is probably similarly large. Just as
there are many ways of classifying chemical compounds (e.g., natural vs. synthetic,
organic vs. inorganic, acid vs. base, biological vs. abiological, stable vs. unstable,
toxic vs. nontoxic, monomers vs. polymers, volatile vs. nonvolatile, and solid vs.
liquid vs. gas), there should be many ways of classifying information. The ones
suggested in Fig.
4.1
and by Turvey and Kugler (1984) may represent just the tip of
the iceberg of information.
The information concept plays a fundamental role in biology akin to the role of
energy in physics and chemistry. The pivotal role of information in biology is
illustrated by the following list of information-related expressions widely used in
biology:
1. Genetic information.
2. The
sequence information
of proteins, RNA, and DNA
3. Functional versus structural information of biopolymers.
4. The
control information
carried by transcription factors.
5. The
regulatory information
encoded in the promoter regions of DNA.
6. DNA carries genetic information.
7. Hormones carry regulatory information.
8. Protein shapes carry the
information
specifying their target ligands or receptors.
9. Intracellular dissipative structures (or dissipatons) carry
genetic information
(called the Prigoginian form of
genetic information
[Ji 1988]).
