Monday, April 13, 2009

DNA – The Secret of Life

DNA – The Secret of Life
Author: James Watson
Publisher: Arrow Books
Pages: 432
Dedication: For Francis Crick.
Nothing can be more rewarding than having a book about DNA straight from one of the co-discoverers of its double helix structure. Francis Crick and James Watson discovered its internal structure in 1953 and were duly awarded the Nobel Prize in Physiology or Medicine in 1962. The style and structure of the book is inimitable. An unbroken chain of sly humour makes it eminently attractive and compels the reader to get stuck to it even though the topic of discussion is pure science and technology. Though Watson was accused of ‘scientific racism’ in his later years, the book presents no such example. On the contrary, his avowed enmity to racism is amply evidenced in his tirades against the proponents of Eugenics in the beginning of last century. Eugenics prompted many states in US to adopt laws for sterilizing people with genetic disorders so that their genes won’t pass along. Many a times, the victims were mainly of African or Asian origins.
Many physicists or would-be physicists took part in the search for DNA. Erwin Schrodinger, who needs no introduction to physics students wrote a book titled, “What is Life?” in which he suggested that the language of life might be like Morse code, a series of dots and dashes. In fact, the language of DNA is a linear series of As, Ts, Gs and Cs. And just as transcribing a page out of a book can result in the odd typo, the rare mistake creeps in when all these As, Ts, Gs and Cs are being copied along a chromosome. These errors are the mutations geneticists had talked about for almost fifty years. Watson was attracted by Schrodinger’s sound logic and Crick was actually a physicist who turned to biology after reading “What is Life?”. He asserts that, “The discovery of the double helix sounded the death knell for vitalism. Serious scientists, even those religiously inclined, realized that a complete understanding of life would not require the revelation of new laws of nature. Life was just a matter of physics and chemistry, albeit exquisitely organized physics and chemistry”.
Watson discusses several genetic disorders, citing the defect at the root of all, in genes. Sickle cell anemia, a genetic disorder common in Africans, makes the red blood cells of victims tend to become deformed, assuming a distinctive “sickle” shape and the resulting blockages in capillaries can be horribly painful, or lethal. The difference between the normal gene and those afflicted with the disease amounted to a single amino acid. Glutamic acid, found at position 6 in the normal protein chain, is replaced, in sickle cell hemoglobin, by valine.
Explanation of GM foods are neat and to the point. Example of BGH is cited. Bovine Growth Hormone (BGH) is similar in many ways to human growth hormone, but it has an agriculturally valuable side effect: it increases milk production in cows. Monsanto Corp cloned the BGH gene and produced recombinant BGH. The milk yield increased by 10%. The milk produced is indistinguishable from that produced by non-supplemented cows. As the GM food debate swirls around us, it is important to appreciate that our custom of eating food that has been genetically modified is actually thousands of years old. In fact, both our domesticated animals, the source of our meat, and the crop plants that furnish our grains, fruits and vegetables, are very far removed genetically from their wild forebears. Agriculture did not suddenly arise, fully fledged, ten thousand years ago. Many of the wild ancestors of crop plants, for example, offered relatively little to the early farmers: they were low yield and hard to grow. Modification was necessary if agriculture was to succeed. Early farmers understood that modification must be bred in if desirable characteristics were to be maintained from generation to generation. And in the absence of gene guns and the like, this activity depended on some form of artificial selection, whereby farmers bred only those individuals exhibiting the desired traits – the cows with the highest milk yield, for example.
Bt Cotton is also explained nicely. Bacillus thuringiensis (Bt) naturally assaults the cells of insect intestines, feasting upon the nutrients released by the damaged cells. The guts of the insects exposed to the bacterium are paralyzed, causing the creatures to die from the combined effects of starvation and tissue damage. First used as a pesticide in France in 1938, the bacterium was originally thought to work only against moth/butterfly caterpillars, but different strains have subsequently proved effective against the larvae of beetles and flies. The success of the mechanism has inspired genetic engineers. Instead of applying the bacterium scattershot to crops, it would be better to engineer the gene for the Bt toxin into the genome of crop plants. The farmer would never again need to dust his crops because every mouthful of the plant would be lethal to the insect ingesting it (and harmless to humans). The method has at least two clear advantages over the traditional dumping of pesticides on crops. First, only insects that actually eat the crop will be exposed to the pesticide; non-pests are not harmed, as they would be with external application. Second, implanting the Bt toxin gene into the plant genome causes it to be produced by every cell of the plant; traditional pesticides are typically applied only to the leaf and stem.
In 1992, UNICEF estimated that some 124 million children around the world were dangerously deficient in vitamin A. The annual result is some half million cases of childhood blindness; many of these children will even die for want of the vitamin. Since rice does not contain vitamin A or its biochemical precursors, these deficient populations are concentrated in parts of the world where rice is the staple diet. An international effort, funded largely by the Rockefeller Foundation has developed what has come to be known as “golden rice”. Though this rice does not contain vitamin A per se, it yields a critical precursor, beta-carotene (which gives carrots their bright orange color and golden rice the fainter orange tint that inspired its name).
Watson led the Human Genome Project (HGP) in its beginning. A 3 billion dollar effort with cooperation across countries and academy and industry helped it become a grand success. The HGP has proved Darwin more right than Darwin himself would ever have dared dream. Molecular similarities stem ultimately from the way in which all organisms are related through common descent. A successful evolutionary ‘invention’ is passed down from one generation to the next. Once evolution solves a particular problem – for example, designing an enzyme to catalyze a particular biochemical reaction – it tends to stick with that solution. Some 46 percent of the proteins we see in yeast also appear in humans. Also, 43% of worm proteins, 61% of fruit fly proteins and 75% of fugu proteins have marked sequence similarities to human proteins. A comparison of the gene count of several species are given.
Common name Number of genes
Human 25,000
Mustard plant 27,000
Nematode worm 20,000
Fruit fly 14,000
Baker’s yeast 6,000
Gut bacterium 4,000
The Neanderthal genes were sequenced successfully. They had more in common with human mitochondrial DNA (mtDNA) than with those of chimpanzees, telling us that Neanderthals were unquestionably part of the human evolutionary lineage. At the same time, however, there were dramatic differences between the Neanderthal sequences and all 986 available sequences of modern human mtDNA. The sum of the genetic evidence leads us to conclude that while Neanderthals do have their place on the evolutionary tree of humans and their relatives, the Neanderthal branch is a long way from the modern human. If, when they encountered each other in Europe 30,000 years ago, Neanderthals and humans had indeed interbred, their mtDNA sequences would have entered the modern human gene pool. That we see no evidence of such input implies that modern humans eliminated the Neanderthals rather than interbreeding with them.
The rationale for skin color is given. Why did people living in higher latitudes lose melanin? The best explanation involves vitamin D3 synthesis, a process carried out in the skin and requiring UV light, D3 is essential for calcium uptake, which in turn is a critical ingredient of strong bones. As our ancestors moved out of Africa into highly seasonal environments, with less year round UV radiation, natural selection favoured pale-skinned variants because they, with less sun blocking pigment in their skin, synthesized D3 more efficiently with the limited UV available. The same logic may apply to the movements of our ancestors within Africa too. The San tribe, for instance, in South Africa, where UV intensities are similar to those of the Mediterranean, have a strikingly pale skin. But what about the Inuit peoples, who live in or close to the hardly sunny Arctic but are surprisingly dark? Their opportunities for producing the vitamin would appear to be further limited by the need to be fully clothed all the time in their climate.
Human genome has a striking similarity to that of the chimpanzee. They have 24 chromosome pairs whereas we have 23. It turns out that our chromosome 2 was produced by the fusion of two chimp chromosomes. There are also differences in chromosomes 9 and 12 and several inversions within chromosomes.
DNA fingerprinting is also explained in detail. This technique was discovered by accident by a British geneticist, Alec Jeffreys. He noticed that a short piece of DNA repeated over and over again and such repeats varied in number from individual to individual. Jeffreys determined that the repeats were junk DNA, not involved in coding for protein, but he was soon to discover that this particular junk could be put to good use.
The book covers all the aspects of genetic research and examines the burning issues in detail and with an endorsement by the author that nothing is amiss in the new technology. When ill informed people rally up against Bt Cotton and GM food, it is very helpful for the society to have a dissenting voice. Watson’s definitive approval lends weight to several counter arguments to have science have its way and keep politics and superstitions away from it.
Overall rating: 5 Star

Saturday, April 4, 2009

Four Elements


Four Elements
Author: Rebecca Rupp
Pages: 351
Publisher: Profile Books
An eminently readable scientific book, presented in an easy to read and simple language. It traces the origins of scientific thought and the quest for elements which are the building blocks of matter. The book presents a historical survey of water, air, fire and earth, the ancient Greek’s fundamental components of the universe. Thales of Miletus posited that water was the basic element of matter. His pupil, Anaximander (610-546 BC) chose earth, Anaximenes (585-525 BC) chose air and Heraclitus chose fire. Empedocles combined all four in a ‘unified theory’. Plato taught his atomic theory in his academy. It was the closing of Plato’s Academy in 529 AD (after 900 years of service) on orders of Justinian that traditionally marks the beginning of the dark ages. Aristotle added the fifth element, ether to the list. Abu Musa Jabir Ibn Hayyan (Geber) postulated that all matter is composed of sulfur and mercury which could then be recombined in a different ratio to generate another metal, say, gold. Effective recombination required a catalyst, which Geber referred to as al-iksir (or elixir). Paracelsus of 15th century combined the Greek and Arabic scholars while Robert Boyle (17th century) refuted all these and built the foundations of modern Chemistry.
The book then delves into varied and interesting data on each of the four elements, beginning with water. A very interesting anecdote is given, proving the gullibility of the unsuspecting public. Nathan Zohner, a student in the US collected signatures of 86% of his class to ban the substance “Dihydrogen Monoxide” which he claimed is responsible for thousands of deaths annually (by accidental inhalation), is a prime component of acid rain, and has been shown to accelerate the corrosion and rusting of many metals. In gaseous form, it causes severe – even fatal – burns. And the stuff is addictive. Dependency on it is irreversible: complete withdrawal results in certain death!
The book then explains water’s molecular structure and properties, water cycles, presence of it in early earth, history of swimming, and on and on. It is an excellent browser’s paradise. So many topics, in so few pages. A perfect beginning for those who want more.
An excellent work by Ms Rupp. Nothing more, nothing less.
Overall rating: 4 Star