Computing vs. Genetics - Advancing Artificial Intelligence Through Biological Process Applications - page 173

Looking at the code, we find that XYC and
XYU always code the same amino acid, whereas
XYG and XYA almost always do. It is clear then
that the first two letters of each codon are signifi-
cant factors, whereas the third appears to be less
important and not to fit in as accurately as the
others. The structural basis for these equivalences
is evident owing to the nature of the anticodons
of the t-RNA molecules. However, and this is
what we want to stress in this paper, the last base
of the codon is fundamental from the functional
viewpoint, as it is the one that will characterise
the behaviour of the protein and the original gene
in which it is located. The generalised degeneracy
of genetic code has two biological implications.
On the one hand, degeneracy reduces the noxious
effects of mutations to a minimum. One plausible
reason why code is degenerated is that redundancy
provides a safety mechanism. But utility is also

a possible ground: it is quite plausible that the
silent mutations may have long-term benefits.
On the other hand, code degeneracy can also be
significant insofar as it allows DNA to largely
modify its base composition without altering the
sequence of amino acids it encodes. The content of
[G] + [C] could encode the same proteins if they
simultaneously used different synonyms.

8. Termination signals: The last characteristic

of the code refers to the fact that of the 64
possible triplets, there are three that do not
encode any amino acid, and these are UAG,
UAA and UGA.

2 TEST

Suppose that we find that a series of events E 1 , E 2 ,
…, E j occur in a given sample with frequencies o 1 ,

Table 2. Genetic code

Position 1
(5' end)

Position 2 Position 3

(3' end)

U C A G

Serine
Serine
Serine
Serine

Tyrosine
Tyrosine
Stop
Stop

Cysteine
Cysteine
Stop
Tryptophan

Phenylalanine
Phenylalanine
Leucine
Leucine

U
C
A
G

U

Arginine
Arginine
Arginine
Arginine

Leucine
Leucine
Leucine
Leucine

Proline
Proline
Proline
Proline

Histidine
Histidine
Glutamine
Glutamine

U
C
A
G

C

Isoleucine
Isoleucine
Isoleucine
Met (Start)

Asparagine
Asparagine
Lysine
Lysine

Threonine
Threonine
Threonine
Threonine

Ser
Ser
Arginine
Arginine

U
C
A
G

A

Valine
Valine
Valine
Valine

Alanine
Alanine
Alanine
Alanine

Aspartic acid
Aspartic acid
Glutamic acid
Glutamic acid

Glycine
Glycine
Glycine
Glycine

U
C
A
G

G

Table 3. Sample with associated frequencies

Event E1 E2 … Ej

Observed frequency o1 o2 … oj

Expected frequency e1 e2 … ej