Following the advent of the Mendelian-chromosome theory of heredity in the s and the maturation of atomic theory and quantum mechanics in the s, such explanations seemed within reach. However, in the s and s it was by no means clear which—if any—cross-disciplinary research would bear fruit; work in colloid chemistry , biophysics and radiation biology , crystallography , and other emerging fields all seemed promising. In , George Beadle and Edward Tatum demonstrated the existence of a precise relationship between genes and proteins.
In , Alfred Hershey and Martha Chase confirmed that the genetic material of the bacteriophage , the virus which infects bacteria, is made up of DNA  see Hershey—Chase experiment. They also hypothesized the existence of an intermediary between DNA and its protein products, which they called messenger RNA. The chief discoveries of molecular biology took place in a period of only about twenty-five years. Another fifteen years were required before new and more sophisticated technologies, united today under the name of genetic engineering , would permit the isolation and characterization of genes, in particular those of highly complex organisms.
If we evaluate the molecular revolution within the context of biological history, it is easy to note that it is the culmination of a long process which began with the first observations through a microscope. The aim of these early researchers was to understand the functioning of living organisms by describing their organization at the microscopic level. From the end of the 18th century, the characterization of the chemical molecules which make up living beings gained increasingly greater attention, along with the birth of physiological chemistry in the 19th century, developed by the German chemist Justus von Liebig and following the birth of biochemistry at the beginning of the 20th, thanks to another German chemist Eduard Buchner.
Between the molecules studied by chemists and the tiny structures visible under the optical microscope, such as the cellular nucleus or the chromosomes, there was an obscure zone, "the world of the ignored dimensions," as it was called by the chemical-physicist Wolfgang Ostwald. This world is populated by colloids , chemical compounds whose structure and properties were not well defined. The successes of molecular biology derived from the exploration of that unknown world by means of the new technologies developed by chemists and physicists: X-ray diffraction , electron microscopy , ultracentrifugization , and electrophoresis.
These studies revealed the structure and function of the macromolecules. A milestone in that process was the work of Linus Pauling in , which for the first time linked the specific genetic mutation in patients with sickle cell disease to a demonstrated change in an individual protein, the hemoglobin in the erythrocytes of heterozygous or homozygous individuals.
The development of molecular biology is also the encounter of two disciplines which made considerable progress in the course of the first thirty years of the twentieth century: biochemistry and genetics. The first studies the structure and function of the molecules which make up living things. Between and , the central processes of metabolism were described: the process of digestion and the absorption of the nutritive elements derived from alimentation, such as the sugars.
Evolution and Molecular Revolution
Every one of these processes is catalyzed by a particular enzyme. Enzymes are proteins, like the antibodies present in blood or the proteins responsible for muscular contraction. As a consequence, the study of proteins, of their structure and synthesis, became one of the principal objectives of biochemists. The second discipline of biology which developed at the beginning of the 20th century is genetics. After the rediscovery of the laws of Mendel through the studies of Hugo de Vries , Carl Correns and Erich von Tschermak in , this science began to take shape thanks to the adoption by Thomas Hunt Morgan , in , of a model organism for genetic studies, the famous fruit fly Drosophila melanogaster.
Shortly after, Morgan showed that the genes are localized on chromosomes. Following this discovery, he continued working with Drosophila and, along with numerous other research groups, confirmed the importance of the gene in the life and development of organisms. Nevertheless, the chemical nature of genes and their mechanisms of action remained a mystery.
Molecular biologists committed themselves to the determination of the structure, and the description of the complex relations between, genes and proteins. The development of molecular biology was not just the fruit of some sort of intrinsic "necessity" in the history of ideas, but was a characteristically historical phenomenon, with all of its unknowns, imponderables and contingencies: the remarkable developments in physics at the beginning of the 20th century highlighted the relative lateness in development in biology, which became the "new frontier" in the search for knowledge about the empirical world.
Moreover, the developments of the theory of information and cybernetics in the s, in response to military exigencies, brought to the new biology a significant number of fertile ideas and, especially, metaphors. The choice of bacteria and of its virus, the bacteriophage, as models for the study of the fundamental mechanisms of life was almost natural - they are the smallest living organisms known to exist - and at the same time the fruit of individual choices. The geographic panorama of the developments of the new biology was conditioned above all by preceding work.
The US, where genetics had developed the most rapidly, and the UK, where there was a coexistence of both genetics and biochemical research of highly advanced levels, were in the avant-garde.
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Germany, the cradle of the revolutions in physics, with the best minds and the most advanced laboratories of genetics in the world, should have had a primary role in the development of molecular biology. But history decided differently: the arrival of the Nazis in - and, to a less extreme degree, the rigidification of totalitarian measures in fascist Italy - caused the emigration of a large number of Jewish and non-Jewish scientists.
The majority of them fled to the US or the UK, providing an extra impulse to the scientific dynamism of those nations. These movements ultimately made molecular biology a truly international science from the very beginnings. They were relatively quick to appreciate the polymeric nature of their "nucleic acid" isolates, but realized only later that nucleotides were of two types—one containing ribose and the other deoxyribose. Friedrich Miescher — discovered a substance he called "nuclein" in Somewhat later, he isolated a pure sample of the material now known as DNA from the sperm of salmon, and in his pupil, Richard Altmann , named it "nucleic acid".
This substance was found to exist only in the chromosomes. In Phoebus Levene at the Rockefeller Institute identified the components the four bases, the sugar and the phosphate chain and he showed that the components of DNA were linked in the order phosphate-sugar-base. He called each of these units a nucleotide and suggested the DNA molecule consisted of a string of nucleotide units linked together through the phosphate groups, which are the 'backbone' of the molecule.
However Levene thought the chain was short and that the bases repeated in the same fixed order. In Nikolai Koltsov proposed that inherited traits would be inherited via a "giant hereditary molecule" which would be made up of "two mirror strands that would replicate in a semi-conservative fashion using each strand as a template". Zimmer published results in suggesting that chromosomes are very large molecules the structure of which can be changed by treatment with X-rays , and that by so changing their structure it was possible to change the heritable characteristics governed by those chromosomes.
He was not able to propose the correct structure but the patterns showed that DNA had a regular structure and therefore it might be possible to deduce what this structure was.
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In , Oswald Theodore Avery and a team of scientists discovered that traits proper to the "smooth" form of the Pneumococcus could be transferred to the "rough" form of the same bacteria merely by making the killed "smooth" S form available to the live "rough" R form. Quite unexpectedly, the living R Pneumococcus bacteria were transformed into a new strain of the S form, and the transferred S characteristics turned out to be heritable.
Avery called the medium of transfer of traits the transforming principle ; he identified DNA as the transforming principle, and not protein as previously thought. He essentially redid Frederick Griffith 's experiment. In the s, three groups made it their goal to determine the structure of DNA. A third group was at Caltech and was led by Linus Pauling. Crick and Watson built physical models using metal rods and balls, in which they incorporated the known chemical structures of the nucleotides, as well as the known position of the linkages joining one nucleotide to the next along the polymer.
Of the three groups, only the London group was able to produce good quality diffraction patterns and thus produce sufficient quantitative data about the structure. In Pauling discovered that many proteins included helical see alpha helix shapes. Pauling had deduced this structure from X-ray patterns and from attempts to physically model the structures. Pauling was also later to suggest an incorrect three chain helical DNA structure based on Astbury's data. Even in the initial diffraction data from DNA by Maurice Wilkins, it was evident that the structure involved helices.
But this insight was only a beginning. There remained the questions of how many strands came together, whether this number was the same for every helix, whether the bases pointed toward the helical axis or away, and ultimately what were the explicit angles and coordinates of all the bonds and atoms. Such questions motivated the modeling efforts of Watson and Crick. Today, something of the reverse is happening with the techniques and approaches developed by evolutionists permeating molecular biology.
For example, phylogenetic analysis plays a critical role in tracing the origins of antibiotic resistance Dantas et al. In the past, this synergy has come awkwardly, perhaps because of a difference in scientific cultures. The book masterfully covers the field of evolutionary biology from a multicultural perspective through the collaborative writings of a population geneticist, paleontologist, microbiologist, human geneticist, and developmental biologist. Like none before it, this book should successfully introduce evolutionary biology to the present generation of students while drawing appropriate connections to molecular foundations, concepts, and the potential for new, integrative directions.
In some ways, Evolution is suitable for any student new to the subject of evolutionary biology. The book is organized into four sections: an overview, the origin and diversification of life, evolutionary processes, and human evolution. The overview combines the history of evolutionary biology with the history of molecular biology. Also sketched are the historical circumstances before the birth of molecular biology; the events leading up to the discovery of the structure of DNA; and the technical advances enabling the study of DNA, RNA, proteins, and their relationship to one another and to the evolutionary process.
The frequent comparison of failed and successful theories simultaneously conveys the excitement of discovery and the fallibility of human effort at the cutting edge of biological science. These chapters are paired and integrated, setting the stage for an extensive summary and interpretation of evidence for evolution and the remainder of the book.
In the meaty midsections of the book, students are presented with the two fundamental aspects of evolutionary biology—pattern emphasizing current knowledge and theories on the origins of life, deep history, and the origins of phylogenetic diversity and process emphasizing the mechanisms of population change. While molecular perspectives are given throughout, the excitement of recent genomic and proteomic advances fortunately do not upstage a clear articulation of the pillars of evolutionary process such as mutation, genetic drift, population structure, and selection.
In fact, these subjects enjoy a spectacular and detailed delivery. Particularly astute analyses center on the role of optimization and constraints, evolutionarily stable strategies, and maintained polymorphisms, bringing together different traditions in evolutionary biology.
Molecular evolution meets the genomics revolution.
The overall treatment is quite thorough, with clear writing and engaging illustrations and photographs. At pages, the book is an intense introduction to evolutionary biology, and students who are serious about digesting the material in this text will gain an impressive perspective on the subject. In other ways, Evolution will not be suitable for some courses. The genetic sophistication and integration of molecular concepts immediately bumps the discussion up to a more advanced level and could easily overwhelm beginning university students. Prior exposure to genetics and molecular biology is critical; without it, the pace through the text will surely be slow.
DNA and amino acid sequence evolution 7.
DNA and amino acid sequence evolution 2 8. DNA and protein sequencing technologies, applications and experimental design considerations 9. DNA and protein sequencing technologies, applications and experimental design considerations Rates and patterns of molecular evolution 1: Rates of mutation and nucleotide substitution, causes of variation, patterns of substitution and replacement Rates and patterns of molecular evolution Molecular phylogenetics and tree construction Molecular phylogenetics and tree construction 2 Reticulate evolution and examples of phylogenetic networks: tree of life, origins of archaebacteria and eukaryotes, domains of life