Biology Reference
In-Depth Information
The double-headed arrow in Step 9 indicates that IDSs and survival actions are
synonymous or identical. This idea has been referred to as the
IDS-cell function
identity hypothesis
(Sect.
10.2
).
11.2.5 Two-Dimensional Genes: The Quality-Quantity
Complementarity of Genes
The currently most widely accepted definition of a gene is “a segment of DNA that
encodes an RNA or a protein molecule.” This definition was probably established
around 1961 when the
triplet genetic code
was discovered (see Table
11.1
and
Crick et al. 1961). Such a definition of a gene is no longer adequate to completely
account for what we can now measure about a gene. For example, the DNA
microarray technique invented in the mid-1990s (see Sect.
12.1
) measures two
aspects of a gene simultaneously: (a) the nucleotide sequence and (b) the copy
number (also called abundance, levels, or concentrations) (see Fig.
11.6
). The
former reflects the qualitative aspect of a gene and the latter reflects the quantitative
aspect, and
quality
and
quantity
are complementary to each other in the Bohrian
the two irreconcilably opposite properties, sequence, and copy number, just as light
can be regarded as the complementary union of irreconcilably opposite waves and
particles (see Sect.
2.3.5
). We may represent this idea algebraically as shown in
Eq.
11.12
:
Gene
¼
½
S
;
CN
(11.12)
where S is the nucleotide
sequence
and CN is copy number. In Fig.
11.6
, Ss are
given in the column on the right-hand side of the figure, and CNs (in relative units)
are indicated on the
y
-axis. Eq.
11.12
also indicates that a gene is two-dimensional,
since a gene is a function of two independent variables, S and CN. Eq.
11.12
also
applies to gene products, RNAs, and proteins.
RNA
¼
½
S
;
CN
(11.12a)
Protein
¼
½
S
;
CN
(11.12b)
The microarray data measured in budding yeast undergoing glucose-galactose
shift (described in Sect.
12.3
) demonstrate that there is a good correlation between
metabolic functions of the cell and the kinetic behavior (or trajectory) of an mRNA
molecule (Sect.
10.2
), leading to the following triple correlation:
Gene X
mRNAX
CellFunction X
(11.12c)
