Information Technology Reference
In-Depth Information
C
T
G
A
Figure 1.1.
Base pairing in the double stranded DNA molecule. Note that the
bulkier G and A pair, respectively, with the smaller C and T, putting the two strands
exactly the same distance apart. Note also that the information contained in one
strand is basically the same contained in the other. In fact, DNA strands are said to
be complementary.
other and are locked in the interior of the double helix. This makes DNA
chemically inert and stable, which are desirable qualities of information keep-
ers. In fact, in the cell, DNA is further protected in the protected environ-
ment of the nucleus in eukaryotes or the nucleoid in prokaryotes. But most
important to us, is that DNA is incapable of both catalytic activity and struc-
tural diversity: first, the potential functional groups (the bases A, T, C and G)
are locked up in the interior of the helix and, second, the molecule lacks
tertiary structure, another prerequisite for catalytic activity and structural
diversity.
Simplifying, DNA may be seen as a long string composed of four different
letters (A, T, C, and G) in which the sequence of the letters (or primary
structure) consists of the genetic information. The genetic information or the
blueprints of all organisms on Earth are written on the four letter language of
DNA. For instance, the average mammal genome contains about 5
X
10
9
base
pairs (or letters, if only one strand is considered) of DNA and codes for
approximately 300,000 protein and RNA genes which are the immediate prod-
ucts of expression of the genome. Below we will see how the genetic infor-
mation is expressed as proteins.
1.1.2 RNA
As I said earlier, in the global picture of information metabolism, RNA might
be seen as a working copy of a particular sequence of DNA. When a protein
gene is expressed, a copy of the gene in the form of messenger RNA (mRNA)
