Montage. DNA is a protein-building code library.
A protein is like a word built of letters (amino acids) which are spelled out along the length of the DNA “page.”

May 26, 2008 – Geneticists of Leiden University Medical Centre (LUMC) are the first to determine the DNA sequence of a woman. She is also the first European whose DNA sequence has been determined. This has been announced by the researchers this morning, during a special press conference at ‘Bessensap’, a yearly meeting of scientists and the press in the Netherlands.

Following in-depth analysis, the sequence will be made public, except incidental privacy-sensitive findings. The results will contribute to insights into human genetic diversity.

DNA of geneticist Marjolein Kriek

The DNA is that of dr Marjolein Kriek, a clinical geneticist at LUMC. “If anyone could properly consider the ramifications of knowing his or her sequence, it is a clinical geneticist,” says professor Gert-Jan B van Ommen, leader of the LUMC team and director of the ‘Center for Medical Systems Biology’ (CMSB), a center of the Netherlands Genomics Initiative.

Van Ommen continues: “Moreover, while women don’t have a Y-chromosome, they have two X-chromosomes. As the X-chromosome is present as a single copy in half the population, the males, it has undergone a harsher selection in human evolution. This has made it less variable. We considered that sequencing only males, for ‘completeness’, slows insight into X-chromosome varialibity. So it was time, after sequencing four males, to balance the genders a bit”. He smiles: “And after Watson we also felt that it was okay to do Kriek”.

Eight times coverage

The DNA sequencing was done with the Illumina 1G equipment. This has been installed in January 2007 in the Leiden Genome Technology Center, the genomics facility of LUMC and CMSB. In total, approx. 22 billion base pairs (the ‘letters’ of the DNA language) were read. That is almost eight times the size of the human genome.’

Dr. Johan den Dunnen, project leader at the Leiden Genome Technology Center: ‘This high coverage is needed to prevent mistakes, connect the separate reads and reduces the chance of occasional uncovered gaps.

Johan den Dunnen: ‘The sequencing itself took about six months. Partly since it was run as a ‘side operation’ filling the empty positions on the machine while running other projects. Would such a job be done in one go, it would take just ten weeks”.

The cost of the project was approximately €40.000.- This does not include further in-depth bioinformatics analysis. This is estimated to take another six months.


In 2001, the DNA sequence was published of a combination of persons. The DNA sequences of Jim Watson, discoverer of the DNA’s double helix structure, followed in 2007, and later the DNA of gene hunter Craig Venter. Recently the completion of the sequences of two Yoruba-Africans was announced.

Source: Leiden University


A remarkably short scientific paper, known officially as a letter, was published on 25 April 1953 in Nature, by James Watson and Francis Crick.

It was perhaps the most momentous paper of the modern era, proposing a structure for the chemical, DNA (Deoxyribose Nucleic Acid), which composes the hereditary material of all living cellular organisms.

The proposed structure – a double helix – rapidly became an icon, aesthetically beautiful, and stunning in its capacity to explain how DNA is replicated in order to transmit the genetic material to the next generation.

The insight that the discovery provided, into how human characteristics arise from our individual genes, created a veritable super-highway of research, ushering in gene therapy for inherited diseases and culminating in the sequencing of the human genome.

The discovery of DNA paved the way for a whole new arena of human endeavour, the biotechnology industry. Now, DNA technology affects everyday lives. Medical and scientific experiments, based on the discovery of DNA, are having a colossal impact on the future.

By David Secko – The first inklings of genetic theory can be traced back to a common human experience: the recognition that a child has features similar to those of its parents. This ancient observation is actually one of the cornerstones of. genetics and its subsequent offspring, molecular biology.

For centuries there was little evidence beyond the anecdotal that transmitted inheritance was a reasonable theory. Though it seemed sensible that a child with the same appearance as its parents likely received these characteristics from them, little evidence supported the notion and instead a good deal of confusion surrounded it. Part of the confusion arose from years of traditional breeding programs that sought to improve the quality of domestic plants and animals. The results were often highly unpredictable, with traits like sterility and disease susceptibility arising in the offspring, apparently from nowhere. Where were these characteristics coming from?

The beginnings of an answer first appeared in a monastery garden located in Brno, Czechoslovakia. It was there that an Augustinian monk named Gregor Mendel (1822-1884) had placed a pea plant, Pisum sativum, with the intention of carrying out a painstakingly long breeding experiment1 (see Figure 1).

Figure 1. Mendel’s experiment

After analyzing 21,000 hybrid plants, Mendel conceived of the idea that individual units of inheritance existed, are discreet, and that two such units (one from the female parent and one form the male parent) combined to produce a characteristic of an offspring [1]. The concept of one unit of inheritance, later to be called a gene, was born.

Modern molecular biology has flowed from Mendel’s concept of transmissible genes. It was a starting point that led biologists to the identification of DNA as the primary genetic material, the uncovering of the biochemical structure of genes, an understanding of how DNA stores and regulates the flow of genetic material, and ultimately the development of techniques that allow for the manipulation of DNA.

Hunting for the Molecular Nature of Elusive Genes

While Mendel grew peas in his garden (around the year 1866) many biologists were focused instead on the use of a microscope to document the appearance of the smallest components of a living organism, the cell. A large variety of cells from different organisms were examined and in each case a similar morphological region called the nucleus was seen. Interestingly, certain dyes were found to stain small discreet bodies in all the different nuclei. These small bodies became known as chromosomes (meaning ‘coloured body’). By the turn of the century the insights Mendel had provided concerning transmissible units of inheritance began to be appreciated, and a fascinating possibility arose: could genes be located on the chromosomes that resided in the nucleus of a cell and somehow be transmitted to the next generation?

A few eyebrows were raised by the question, as it suddenly seemed possible that Mendel’s transmissible genes were actually cellular structures, which meant that they were both physically identifiable and could be subject to experimentation. Understandably, excitement about the subject grew. The wait for further breakthroughs was not long, as discoveries began to trickle out of Columbia University (USA) between 1905-1915. There, careful microscopic observation detected chromosomal differences between the sexes: the presence of two X chromosomes in cells from a female, and one X chromosome and one smaller chromosome shaped like a Y in the cells of a male [2]. Not only was it found that these chromosomes determined sex (XX = female, XY = male), but it was also shown that certain traits (and thus their genes) were transmitted only with the X chromosome [3] (see Figure 2).

Figure 2. T.H. Morgan’s Experiment

With chromosomes implicated in carrying the genes responsible for inheritance the question crossing every scientists mind was what were chromosomes made of?

It was here that a turning point was achieved. As biologists turned to the nucleus, trying to define the molecular nature of the chromosome, a shift in the field of biology occurred. In the years to come, the molecular biologish would take centre stage as the hunt for the molecular structure of a gene continued.

Methods available at the time made it very difficult to obtain a pure preparation of chromosomes, they were always contaminated with other cellular components. Nevertheless, it was discovered that chromosomes contained two components: (1) deoxyribonucleic acid, or DNA (commonly abbreviated to nucleic acid), and (2) basic proteins called histones. Even though DNA was present in much higher quantities than protein in these preparations, it was hotly debated whether or not the DNA or histones carried the genes biologists were looking for. A crucial point that kept biological circles divided was the relative structural simplicity of DNA, which was made up of four building blocks, as compared to the complexity of proteins, which were made up of 20 building blocks. Scientific opinion differed on what kind of structural complexity genes would require to dictate the intricacies of a cell; thus whether the cell used a “genetic protein” or “genetic DNA.” It took significant effort to resolve this debate, but in 1952 (many years after the 1915 studies on chromosomes) Alfred Hershey and Martha Chase [4] were able to use different radioisotopes to label proteins (35S) and DNA (32P). This technique allowed them to reveal that bacterial viruses, which were composed only of protein and DNA, reproduced themselves within bacteria by using only their DNA component. Thus, the debate was resolved: genes were made of DNA.

The Biochemical Structure of DNA is Unraveled

While the debate fumed over “genetic protein” versus “genetic DNA” in the 1920s, much about the chemical nature of nucleic acid was elucidated [5]. It was found to be composed of regularly repeating subunits called nucleotides. Only a limited number of nucleotides were found to exist in nature and all contained three elements: (i) a phosphate group(s) linked to a (ii) sugar, which was joined to a (iii) flat ring molecule commonly called a base (see Figure 3). The limited number of natural nucleotides is partially a result of the fact that only five types of natural bases exist: guanine (G), adenine (A), cytosine (C), thymine (T), and uracil (U). Each nucleotide was found to possess the ability to link to others to form chains. Surprisingly, only two similar types of chains existed, DNA and RNA. The most obvious difference between the two types was that the base uracil was only found in RNA, while the base thymine was found only in DNA.

Figure 3. The DNA double helix.

With the relatively simple chemical composition of DNA understood, a more philosophical question still remained: how did DNA govern and dictate the natural variety of life on Earth? This question boiled down to a crucial missing link, how the chemical structure of DNA, essentially a chain of nucleotides linked together, enabled it to act as a carrier of inheritance.

As this question was being asked, another interesting fact was obtained about the chemical characteristics of nucleotides; their bases (G, A, C, T, U) could chemically bind to each other. Not only that, they did so in an exceptionally specific manner. Adenine bound only to thymine in DNA (and uracil in RNA), while guanine bound only cytosine. As a consequence of this the amount of adenine equaled the amount of thymine, while the amount of guanine equaled the amount of cytosine in a DNA molecule [5]. This was later known as Chargaff’s rule, after the Austrian chemist Erwin Chargaff.

Soon after this was discovered, X-ray diffraction studies showed that DNA adopted a regular and precise helical structure. Enough data was now in place for a famous leap of scientific faith to be taken. In 1953, Watson and Crick [6] correctly deduced that DNA forms a double helix with two strands of nucleotides wrapped around each other (see Figure 3). The binding rules for nucleotides ensured that each strand was a complementary copy of the other (for example an adenine in one strand was always bound to thymine in the other strand). Thus, the two strands were complementary anti-parallel chains of nucleotides wound around each other to form a double helix. Our understanding of the molecular nature of inheritance took a step forward with Watson and Crick’s leap of logic, for it was immediately understood that such a structure would provide DNA with a simple mechanism to accurately reproduce itself: just pull the two strands apart and use one strand to create a complementary copy of the other using the nucleotide binding rules [7]. If done for both strands, two exact copies of the original DNA molecule would be created, a process eventually shown to be exactly the way DNA is copied in a cell.

The realization that DNA formed a double helix solved a large part of the question of how DNA was involved in all lifeforms by revealing how to make endless copies of a DNA molecule. But it would still be years before the molecular mechanism of inheritance was fully understood.

Cracking the Genetic Code

At the turn of the 20th century many scientists were beginning to turn their attention to the biochemical basis of heredity. Investigators in many disciplines wanted to understand the underlying biochemistry that dictated the physical appearance of an organism. The study of proteins took center stage. Of particular interest was an important class of proteins, termed enzymes. These proteins were able to catalyze biochemical reactions and were soon found to be responsible for biochemical function. During this period it was determined that proteins were composed of 20 naturally occurring amino acids linked together in a chain (called a polypeptide), much like DNA.

Even before the composition of genes was known, a link between proteins and genes was evident from the study of diseases in which cells fail to perform known biochemical reactions. An example was alkaptonuria, a rare genetic disease resulting from a failure to correctly breakdown two amino acids (phenylalanine and tyrosine) found in a regular diet. The build up of by-products from this blocked pathway produces the black urine characteristic of a patient with the disease. In 1908, Archibold Garrod [8] correctly surmised that the absence or deficiency of a given enzyme required for normal cellular biochemistry, in the case of alkaptonuria it was an absence of an enzyme required to break down amino acids, resulted in a metabolic disease. Since such defects in proteins could be inherited, it appeared that genes could dictate the production of the proteins in an organism. It took almost three decades for adequate knowledge to be gained about cellular metabolism to determine if Archibold Garrod’s link between genes and proteins was true. In the end, it was once again studies of defects in well-known metabolic reactions that showed that a gene directed the production of a single protein, a fact which is now generalized as the “one gene = one protein” rule.

The “one gene = one protein” rule and the understanding that genetic information is specified in the four nucleotide bases of DNA (A, C, G and T) led to a period of scientific excitement in which scientists wondered how four bases of DNA could encode the 20 known amino acids that make up proteins? By the 1950’s, scientists simply assumed the linear sequence of nucleotides in a DNA strand corresponded to the linear sequence of amino acids in a protein polypeptide. The first biochemical evidence of this assumption was that the position of mutations in a protein correlated to the position of mutations is a gene (i.e. they appeared in the same relative places in the molecules). A co-linear relationship seemed to exist between the two. A quick mathematical calculation determined that at least three nucleotides would be required to specify each of the 20 natural amino acids, since blocks of two nucleotides could only be combined to code for 16 of the 20 known amino acids and single nucleotides could only code for four. Random combination of four nucleotides produces 64 possible triplets, but it was not clear at the time how these 64 combinations would code for 20 amino acids.

In 1961, a historic set of experiments were begun by Marshall Nirenberg and Heinrich Matthaei [9] that solved the above question and marked the beginning of modern molecular biological techniques. They were able to create a synthetic nucleotide chain composed only of uracil (i.e. UUUUU), which they went on to add to cells that had been broken apart. When they did this they witnessed the production of a polypeptide chain. Even more interesting, it was composed of only a single amino acid, phenylalanine. Next, they began adding defined lengths of uracil chains to the extracts. By doing this they found that only multiplies of three nucleotides produced amino acid chains. For example, a chain of three uracils (UUU) gave a single phenylalanine, similarly a chain of four or five uracils (UUU-U or UUU-UU) also produced only one phenylalanine, while a chain of six (UUU-UUU) produced two phenylalanines linked together. Hence it was determined that a triplet of uracils in a gene coded for the amino acid phenylalanine in a protein. Production of all the possible combinations of three nucleotides (called a codon) soon revealed which triplets coded for which amino acids. It was found that 61 combinations coded for the 20 amino acids, while the three remaining codons were used as “stop” signals for the end of a protein.

The genetic code was now broken. Scientists understood how a protein was encoded in the molecular structure of DNA. With this information it was not long before the underlying mechanisms of how a cell used DNA to make protein became clear.

Producing Genetic Messages from DNA

All living organisms depend upon the production of proteins encoded by the information held within their DNA. Despite the variations that exist between organisms, it was soon found that all cells make use of the same general mechanism for decoding the information in DNA into proteins, termed gene expression. Even though the amino acid sequence of proteins is dictated by the nucleotide sequence of many genes, proteins are not directly synthesized from DNA. Instead, genes produce proteins in two discreet stages, which involve many different types of enzymes, proteins and RNA molecules.

The first stage is called transcription (see Figure 4), in which an RNA copy (or transcript) of a specific gene is produced. This RNA copy of the gene is called a messenger RNA (mRNA), since it is the genetic message that will produce a protein. Production of mRNA requires an enzyme called RNA polymerase. It begins the process by binding to specific nucleotide sequences in the DNA (called a promoter), located just up from the gene that specifies a protein. A complex process unwinds the DNA in this area so that the polymerase can begin to move along the DNA strand like a train along a rail. As the RNA polymerase moves along it synthesizes an RNA copy according to the nucleotide sequence it encounters (done by pairing a new nucleotide to a complementary nucleotide in the DNA using the base pairing rules, followed by linking them together). This procedure continues until the polymerase hits a defined sequence called a terminator, which causes the polymerase to fall off the gene and release the mRNA. Once released, an mRNA is free to float through the cell bearing its genetic message and ultimately engages in the second stage of producing a protein from a gene.

Figure 4. DNA transcription and translation.

ecoding Genetic Messages

The process of decoding mRNA transcripts is termed translation and once again involves many types of proteins and RNA molecules. In particular, translation requires two types of RNA termed ribosomal RNA (rRNA) and transfer RNA (tRNA). Ribosomal RNA is intimately involved in the synthesis of proteins through the interaction of various types of rRNA to form a complex called a ribosome. This is the cellular machine that creates proteins from mRNA. A ribosome forms a donut structure with the mRNA passing through its center; a specific site within the mRNA (called the ribosome binding site or RBS) then binds to the ribosome, causing the second type of RNA, the tRNA, to spring into action. tRNAs are universal adaptor molecules that carry amino acids and a complementary triplet of nucleotides called an anti-codon that recognizes each codon in an mRNA. As mentioned before, codon is the name given to triplets of nucleotides in mRNA that code for particular amino acids. An anti-codon is just a complement of a codon. Through this method each triplet in an mRNA molecule will bind to a tRNA that bears its complementary triplet codon. For example, a string of A-U-G nucleotides in an mRNA will bind a tRNA that has a U-A-C triplet, all of which is based on the nucleotide binding rules. Since each tRNA molecule carries an amino acid, the triplet codon will result in a specific amino acid being brought to the ribosome. At the ribosome these amino acids are bound together into a polypeptide chain (i.e. a protein) in exactly the linear order that the mRNA dictates, a sequential process that will produce a protein corresponding directly to the nucleotides in the mRNA.

Central Dogma of Molecular Biology

Over a century of work has gone into the current framework of molecular biology, but at its core, our understanding can be broken down to what has become known as “the central dogma” of molecular biology: DNA is copied into genetic messages, which are then translated into proteins that go on to perform the underlying biochemistry of an organism.

The hunt to understand inheritance has been an important scientific journey. It has required a broad range of disciplines, from chemistry to microbiology to zoology, as well as the development of many new and exciting technologies. This integration of disciplines, combined with the resolution of many engineering difficulties, eventually resulted in the emergence of the field of biotechnology,an exciting enterprise that is bringing molecular biology to the forefront of society and causing us to reshape the way we see the world.

Shareholder Rebellion Ruffling Feathers at Exxon Mobil

By Clifford Krauss, May 27, 2008, Houston, The New York Times — The Rockefeller family built one of the great American fortunes by supplying the nation with oil. Now history has come full circle: some family members say it is time to start moving beyond the oil age.

The family members have thrown their support behind a shareholder rebellion that is ruffling feathers at Exxon Mobil, the giant oil company descended from John D. Rockefeller’s Standard Oil Trust.

Three of the resolutions, to be voted on at the company’s shareholder meeting on Wednesday, are considered unlikely to pass, even with Rockefeller family support.

The resolutions ask Exxon to take the threat of global warming more seriously and look for alternatives to spewing greenhouse gases into the air.

One resolution would urge the company to study the impact of global warming on poor countries, another would encourage Exxon to reduce its emissions and a third would encourage it to do more research on renewable energy sources like solar panels and wind turbines.

A fourth resolution, which the Rockefellers are most united in supporting, is considered more likely to pass. It would strip Rex W. Tillerson of his position as chairman of Exxon’s board, forcing the company to separate that job from the chief executive’s job.

A shareholder vote in favor of that idea would be a rebuke of Mr. Tillerson, who is widely perceived as more resistant than other oil chieftains to investing in alternative energy.

The Rockefellers say they are not trying to embarrass Mr. Tillerson, also Exxon’s chief executive, but think it is time for the company to spend more of its funds helping the nation chart a new energy future.

“Exxon Mobil needs to reconnect with the forward-looking and entrepreneurial vision of my great-grandfather,” Neva Rockefeller Goodwin, a Tufts University economist, said in a statement to reporters.

“The truth is that Exxon Mobil is profiting in the short term from investments and decisions made many years ago, and by focusing on a narrow path that ignores the rapidly shifting energy landscape around the world,” she added.

The resolution on Exxon’s chairmanship was offered for several years before the Rockefellers became publicly involved and last year was supported by 40 percent of shareholders who voted. Royal Dutch Shell and BP already separate the positions of chairman and chief executive, as do many other companies.

“You need a board asking the tough questions,” Peter O’Neill, a private equity investor and great-great-grandson of John D. Rockefeller, said in an interview. “We expect the company to figure out how in this changing world to adjust.”

Kenneth P. Cohen, vice president for public affairs at Exxon, said the shareholders pushing the resolutions were “starting from a false premise.” He added that the company was already concerned about “how to provide the world the energy it needs while at the same time reducing fossil fuel use and greenhouse gas emissions.”

Fifteen members of the family are sponsoring or co-sponsoring the four resolutions, but it appears that some have much more solid support in the sprawling family than others.

Mr. O’Neill said that 73 out of 78 adult descendants of John D. Rockefeller were supporting the family effort to divide the chief executive and chairman positions. The goal of that resolution is to improve the management of the company, which could strengthen its environmental policies and improve more traditional pursuits like exploring more aggressively for new oil reserves.

David Rockefeller, retired chairman of Chase Manhattan Bank and patriarch of the family, issued a statement saying, “I support my family’s efforts to sharpen Exxon Mobil’s focus on the environmental crisis facing all of us.”

The Rockefeller family has always been identified with oil and the legacy of Standard Oil, but for several generations, it has also been active in environmental causes and acquiring land for preservation. John D. Rockefeller’s grandsons devoted themselves to conservation issues, and Rockefeller charitable organizations have long promoted efforts to fight pollution.

Ms. Goodwin, one of the most vocal Rockefellers on the environment today, is co-director of the Global Development and Environment Institute at Tufts.

In recent years, family members have quietly encouraged Exxon executives to take global warming seriously, but their private efforts did not go far. Until now, they have avoided publicity in their efforts, and the youngest Rockefeller generations have generally shunned attention.

Exxon executives said the company spent $2 billion over the last five years on programs to reduce emissions and improve efficiencies and had plans to spend $800 million on similar initiatives over the next three years. They said the company reduced the release of greenhouse gases from its operations last year by 3 percent, and it was working with Stanford to research biofuels and solar and hydrogen energy.

Since taking over the company two years ago, Mr. Tillerson has gradually shifted the company’s positions away from those of his predecessor, Lee R. Raymond, who was considered a skeptic on the science of global warming.

But with gasoline prices soaring and concern growing over global warming, Exxon, the biggest of the investor-owned oil companies, is a target for politicians and environmentalists. Chevron, BP and Shell, Exxon’s largest competitors, have given their investments in renewable fuels a much higher profile.

Similar or identical environmental proposals have not passed at previous Exxon shareholder meetings, but the public support of the Rockefeller family has given old efforts new energy.

The involvement of the Rockefellers, said Robert A. G. Monks, a shareholder who has been urging a separation of the chairman and chief executive jobs for years, shows that “this is not just a matter of the self-appointed good guys against the cavemen, but also a matter of the capitalists wanting to make money.”

Nineteen institutional investors with 91 million shares announced last week that they would support resolutions asking Exxon to separate the top executive positions and tackle global warming. They included the California Public Employees’ Retirement System, the California State Teachers’ Retirement System and the New York City Employees’ Retirement System.

California’s treasurer, Bill Lockyer, who serves on the boards of the two California funds, said the company’s “go-slow approach” on global warming “places long-term shareholder value at risk.”

Under Exxon’s rules, a shareholder proposal that passes is not binding without the support of the board. But Andrew Logan, director of the oil program at Ceres, a coalition of institutional investors and environmentalists, said, “boards tend to strongly consider proposals that get significant support.”

Paul Sankey, an oil analyst at Deutsche Bank, said that he thought a separation of the chief executive and chairman jobs might be a good management move and that “we might see a mild benefit to Exxon’s public image.” But he added, “On balance, we wouldn’t expect any change in strategy.”

The Fraternal Order of Police, which represents public safety officers, whose pensions are invested in Exxon, has publicly opposed the shareholder effort to change company policy.

“The Rockefeller resolution threatens to degrade the value of Exxon Mobil,” the organization wrote in a letter to Mr. Tillerson that criticized the splitting of the top executive jobs.