The genomic medicine

A section of DNA; the sequence of the plate-li...

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Hi guys,

check this video out. The general scientific director of National Human Genome Research Institute is showing how to purify DNA from Strawberry by using everyday household items. It is absolutely a fantastic idea that clarifies also the basic chemical principle of the DNA. After all purifying DNA is not so complicate!

Dr. Erik D. Green started his pioneering studies for whole genome analysis during his post-doc at the Washington University School of Medicine genetics department. His complete biography can be found here. Dr. Green has recently published a very interesting review on the achievement of scientific community in the field of genomic with the title: “Charting a course for genomic medicine from base to bedside”. He summarizes 5 principal achievements: understanding the structure of the genome, understanding the biology of the genome, understanding the biology of the disease, advancing the science of medicine and finally improving the effectiveness of health care (by the 2020!). Very interesting review full of very usefull link. Enjoy the reading.

Arsenic instead of Phosphorus: the extreme adaptation of living creatures.

The structure of deoxyribonucleic acid (DNA), ...

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Since the discovery of the DNA structure by Watson and Crick in 1953, molecular biology has revealed most of the secrets of life. Biologists discovered that any living organisms, from plants to bacteria and from algae to men, are made of cells that use DNA with the same structure and composition as information database for the production of proteins constituted with the same 20 Aa. All the basic mechanism of DNA replication and protein assembling is highly chemically (mostly carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus) and functionally conserved.

The work of Wolfe-Simon and colleagues subvert completely this view. With a selection procedure using a medium inoculated with Mono lake sediments rich in arsenic, they purified a bacterial clone  (called GFAJ-1)  that is not only able to growth in presence of arsenic (probably by expressing proteins that reduces his toxicity) but also to use AsO4-3 (that correspond to physiological composition of phosphorus: PO4-3) as a building brick for DNA and other basic molecules.

 

In the figures, it is possible compare the bacteria grown in phosphorus (left) and the ones grown in arsenic (right). The latter show a swollen shape probably due to large vacuole-like regions, structures not explained by the authors.

They further analyzed the bacteria ability to proliferate (although very slowly, 1 duplication every 10 days) in presence of arsenate showing that is slower than in presence of phosphorus but quicker than in absence of both arsenate and phosphorus. In addition they performed a detailed analysis of bio-molecule composition with particular interest in DNA molecule using mass spectrometry techniques. In the authors point of view, their results demonstrate that arsenic participate to DNA formation, replacing phosphorus.

Here is an interesting interview to the authors of this research:

Controversial issues

As expected, such important statement is strongly debated in the scientific community. The results of this paper may be in conflict with the chemical laws as we know them. Therefore strong experimental evidences are needed in order to support these findings. And this is maybe the weakest point of this work: the experimental evidences have strong limitations and many gaps that make biologists and chemists be skeptical of this high impact paper. Dr. Rosie Redfield exposes very well the limitations of the experimental work on her blog (http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html)