Biology Reference
In-Depth Information
Table 10.2 The five classes of factors affecting the behavior of living cells
Determinants
Examples
Explanations
1. DNA
Mutations in certain genes (e.g., p53
gene [Levine et al. 2004]) lead
to cancer and other pathological
consequences
Mutated genes lead to alterations in
protein amino acid sequences
which often lead to altered protein
conformations and functions
2. RNA
Colon cancer cells show statistically
significantly different patterns
of changes in mRNA levels
compared to those of normal
cells (Stengel 2005)
RNA molecules not only mediate
(through mRNA) but also regulate
(through snRNA, and microRNA,
etc.) the coupling between
genotypes (DNA) and phenotypes
(proteins)
3. Proteins
A diarylquinoline drug, known as
R207910, binds to the membrane
component of the ATP synthase
in
Mycobacterium tuberculosis
,
thereby killing the organism
(Andries et al. 2005)
Proteins are the only macromolecules
in the cell (except ribozymes) that
can harvest free energy from
chemical reactions by catalyzing
them. This means that, without
proteins, no energy-requiring
processes (without which no life
can exist) can be carried out by the
cell. Proteins are molecular
engines/motors/rotors/machines
out of which the cell is constructed
(Alberts 1998) (Chap.
10
)
4. Biochemicals Depriving oxygen kills all aerobic
cells
Without biochemicals, no chemical
reactions can occur inside the cell,
depriving the cell of all free energy
sources and hence of life
5. Environment Most cells can survive only within
narrow ranges of environmental
conditions to which they have
adapted through long
evolutionary history, including
temperature, pressure, humidity,
neighboring cells, radiation,
and nutrient chemicals, etc.
Most cells have evolved to survive and
perform their specialized functions
only under stringently defined
environmental conditions. For
example, although all the cells in
the human body have about 25,000
genes, different subsets of them
are expressed in different parts
of our body, depending on their
micro-environmental conditions
,
leading to the liver, the kidneys,
the heart, or the brain, etc.
Several testable predictions in the field of DNAmicroarray technology (Alon et al.
1999) may be formulated based on the model of the cell shown in Fig.
10.2
:
1. When the level of a mRNA molecule changes in a cell due to some perturbations,
it is impossible to attribute such changes solely to DNA changes (e.g., changes in
transcription rates), because proteins (e.g., transcription factors, RNA polymerase,
histones, DNA topoisomerases, etc.), biochemicals (e.g., ions, pH, ATP, etc.), and
environmental conditions (e.g., tissue specificity, microcirculatory situations,
neighboring cells, etc.) may be responsible for a part or all of the changes in
mRNA levels being measured (cf. the “equipotency hypothesis” above).
