FIFTY YEARS
OF DNA DISCOVERY: CONTROVERSIES OLD AND NEW
Dinesh
C Sharma*
The year 2003
is very significant in the history of modern science. This year
marks 50 years of the discovery of the DNA double helix by James
Watson and Francis Crick, as well as 25 years of the first test-tube
baby, pioneered by Robert Edwards and Patrick Steptoe. These are
not ordinary celebrations when the work of scientists concerned
is remembered and customary tributes are paid. These discoveries
heralded a new era in modern biology. Building on them the world
today is at the verge of another revolution in biology. From double
helix, we have moved to the mapping of human genome. And from
test-tube babies, we have moved to the era of human cloning. Both
these developments have immense significance for the human race,
as scientists start playing with life.
DNA is often referred
to as the molecule of life. Genes are instructions that give organisms
their characteristics. And these instructions are stored in each
cell of every living organism in a long string-like molecule called
deoxyribonuleic acid or DNA. DNA molecules are subdivided into
finite structures called chromosomes. In humans the number of
chromosomes is 46 (23 pairs) and this complete set of genetic
information is called genome.
The DNA molecule
takes the form of a double helix that resembles a long spiral
staircase. The rungs linking the two sides of the staircase are
composed of pairs of nucleotides – either adenine and thymine
or cytosine and guanine. A, T, G and C letters are used to denote
these nucleotides. Particular combinations of these DNA base pairs
or genes contain coded instructions for formation and functioning
of proteins which make up the body and govern its biological functioning.
In other words, they control biological processes required for
an organism to live and reproduce. There are nearly 3 billion
rungs. If unwound, DNA would stretch over five feet, but it is
only 50 trillionth of an inch wide! If the total amount of DNA
in 100 trillion or so cells in human body is laid end-to-end,
it would run to the sun and back some 20 times.
When we talk about
human genome sequencing and mapping, we are actually talking of
sequencing the DNA. "Sequencing" is the process of determining
specific order and identity of the three billion base pairs, with
the ultimate objective of identifying all the genes. "Mapping"
is the process of identifying discrete DNA segments of known position
on a chromosome which can then be used for sequencing. Having
the sequence of the human genome is only a fist step in finding
the genes, understanding how they operate and how particular genetic
irregularities are linked with diseases. Using this DNA information
to diagnose, prevent or treat diseases is the second step - a
complicated task engaging all modern biologists.
The discovery of
DNA structure heralded a revolution in understanding human biology
at molecular level. In India, pioneering work was done by G N
Ramachandran (1922-2001) and his colleagues in the area of structural
studies on proteins. His research in molecular biophysics attracted
scientists from various streams including mathematics and computer
science. "Ramchanadran Plot", devised in early 1960s,
still remains the simplest and the most commonly used tool for
the validation of protein structures. His contribution to x-ray
crystallography have been immense, and he made major contributions
in the area of image reconstruction ("Ramachandran effect").
India’s presence in cutting edge areas of bioinformatics today
is in some way attributed to Ramachandran research.
James Watson, who
currently heads Cold Spring Harbor Laboratory in New York, has
remained active and has been in the thick of the debate on the
human genome project. He has also been at the centre of controversies
– 50 years ago and now in 2003. When Watson and Crick announced
their discovery in the scientific journal, Nature, and
subsequently got the Nobel Prize, there was controversy in the
scientific circles. It was pointed out that the duo had ignored
the role played by another scientist Rosalind Franklin, and also
of Erwin Chargaff. According to Crick, it was only after he and
Watson completed their DNA model that they got access to Rosalind’s
x-ray diffraction data and realized the extent to which they supported
the model. The controversy on credit for the double helix discovery
got revived, and some new evidence is to be released shortly.
This week, Watson
has landed in another ethical controversy relating to the genome
data. He has suggested that genetic engineering could be used
to tinker with human traits. For instance, he has said that stupidity
is a disease and it can be cured! In a message to Indian scientists
last month, he spoke about "manipulating" genetic information.
He said "through working out and later manipulating the sequences
of A, T G and C letters, we will increasingly be able to understand
life at the molecular level and use this knowledge to improve
the quality of human life".
In fact, Watson has
opened a Pandora’s Box of ethical issues of how and which genetic
information is to be used in what way. About 5000 human diseases
are known to have a genetic component, and 1000 disease-associated
markers or genes have already been isolated. We are very close
to having power over the genetic destiny of human species. The
new science is throwing up grave social and moral questions that
need to be addressed. Perhaps the most important question to be
asked in the golden jubilee year of double helix discovery is:
are we ready to let scientists play god?(PIB Features)
*Senior
Science Writer
