QPMPA Journal September 2011 - Qualified Private Medical ...

science
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Francois Jacob, Jacques Monod and
their colleagues discovered that genes
were co-ordinately controlled. E. coli does
not make enzymes for metabolizing sugar
in milk, but when placed in a medium
with lactose, genes to produce enzymes
metabolizing that sugar are induced.
Work showed that the inducer (whatever
it may be) deactivated a repressor and
stopped synthesis of the messenger RNA.
The group of co-ordinately controlled
genes and their regulatory DNA sites was
called “Operon”. It was assumed that
this model might prove to be the way
genes control organisms undergoing
embryological development.
As most cells in developing organisms
seemed to have the same amount of DNA,
it had long been a puzzle how they differentiated
into the many different cell types
in the body. However, further work
showed that gene regulation is far more
complex. In addition, behaviour of the
nervous system was found to be extremely
strange at molecular level. Returning to
fruit flies, Seymour Benzer induced behavioural
mutations in it. Sydney Brenner
developed the nematode worm,
Caenorhabditis elegans, to study its nervous
system and genetics of behaviour.
Nirenberg used neuroblastomas to study
development of neural tissue.
Molecular biology enabled numerous
other fields to go molecular. Descriptive
cytology turned into molecular. The immunological
relationship between antibodies
and antigens was re-characterized
at the molecular level. However, not
all attempts to find the molecular basis
of biological phenomena met with success,
like the claim that RNA molecules
coded memories. In the 1970s, molecular
biology itself was going genomic. The
genome is a collection of nucleic acid
base pairs (adenine pairs with thymine
and cytosine with guanine). The number
of base pairs varies widely among species.
For example, H. influenza has
roughly 1.9 million base pairs while a
Watson
Homo sapiens sapiens has more than
3 billion. Genomics owes much to the
development of new computational
methods for producing, storing, and interpreting
long sequences of enormous
amounts of data.
Frederick Sanger developed proteinsequencing
techniques and used them
to elucidate the amino acid sequence of
insulin. Kary Mullis developed polymerase
chain reaction, a procedure wherein
small samples of DNA were amplified. In
the mid 1980s, USA originated a project
to sequence human genome (initially to
determine the impact of radiation on
humans induced by atom bombs in Japan).
While the human genome received
most of public attention, hundreds of
other genomes including cat, mouse, and
rice were sequenced. One of the startling
revelations was… the human genome
contained 20,000 to 25,000 genes; the
Crick
cats have 20,285 genes, the mouse
24,174, and rice a whopping 50,000. Rice
was more complex than man was. However,
just as a number of disciplines “went
molecular”, molecular biology itself was
wrestling with complexities posed by split
genes and overlapping genes and how a
mere 20,000 genes can construct a human
while a grain of rice requires 50,000
genes. Thus, genomics is now supplemented
by post-genomics.
Developments in genomics and postgenomics
have sparked a number of
philosophical questions about molecular
biology. Since the genome requires a
vast array of other equally indispensable
mechanisms to make a protein product,
can DNA alone really be causally
prioritized. Similarly, in the face of such
interdependent mechanisms involved in
transcription, regulation, and expression,
can DNA alone be privileged as the bearer
of hereditary information? Or is the information
distributed across all such
entities and activities? In addition, if so,
how should be this systems-level analysis
conceptualized? Is post-genomics
simply a collection of mechanisms, or is
there ‘something’ epistemologically and
metaphysically stable that controls systems
and mechanisms? What actually is
this ‘information?’
Genes as linear DNA sequences of bases
carry “information” for the production
of proteins. During protein synthesis,
the information is “transcribed” from
DNA to messenger RNA and then translated
to proteins. During DNA replication,
and subsequent inheritance, it is
often said that what is passed to the
next generation is the “information” in
the genes, namely the linear ordering
of bases along DNA strands. Historians
of biology have tracked the information-talk
of molecular biology, and
philosophers of biology have doubted
whether a definition of “information”
can be provided at all that adequately
captures its usage in this field.
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QPMPA.JMS . Vol. XXV . No. 3 . June-Sept. 2011