Except for mutations, which are "chance" occurrences that go through the screen of natural selection, DNA is replicated invariantly, and this constitutes the necessity part of Monods argument. DNAs information for the proteins is directed. As opposed to a teleological pulling toward some end product, Monod calls this directional vector teleonomic. The end products of this are all the various life forms in our biosphere.
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Hic communionis quae cogito lego, et in libris philosophorum leguntur: Percy C. Different cells work in different ways at different times, however. This too is regulated by genes. In Jacob and Monod proposed the existence of a messenger ribonucleic acid mRNA , a substance whose base sequence is complementary to that of deoxyribonucleic acid DNA in the cell.
In advancing the concept of gene complexes that they called operons, Jacob and Monod postulated the existence of a class of genes that regulate the function of other genes by affecting the synthesis of messenger RNA. For this work, which has been proved generally correct for bacteria, the two men were awarded a Nobel Prize.
Monod joined the staff of the Pasteur Institute in Paris in and became its director in Chance and Necessity. The basic tenet of this book is that systems in nature with molecular biology, such as enzymatic biofeedback loops can be explained without having to invoke final causality. Teleonomic In this book, Monod adopted the term teleonomic to permit recognition of purpose in biology without appealing to a final cause.
He goes on to explain that it is marginal because the living world is only a fraction of the universe. He goes on to state that he does not intend to make a thorough survey of modern biology but rather to "bring out the form of its key concepts and to point out their logical relationships with other areas of thought…it is an avowed attempt to extract the quintessence of the molecular theory of the code" Monod, xiii.
Monod stresses the importance of the molecular theory of the genetic code as a physical theory of heredity and brands it as the "secret of life". He continues to explain how this important discovery has made it the duty of scientists to share with and enhance other disciplines of thought such as philosophy. Toward the end of the preface Monod offers apology for any overly tedious or technical sections. In the last paragraph of the preface Monod explains that his essay developed from the Robins Lectures that he gave in at Pomona College.
Of strange objects Monod starts off chapter I entitled "Of Strange Objects" with a consideration of the difference between natural and artificial objects and states that "the basic premise of the scientific method Through a series of thought experiments and rhetorical questions he leads the reader on a difficult path to three characteristics of living beings. One is teleonomy which Monod defines as the characteristic of being "endowed with a purpose or project" Monod, 9.
Monod offers a single exception to this last criterion in the form of a crystal and at this point he states that the internal forces that determine structure within living beings are "of the same nature as the microscopic interactions responsible for crystalline morphologies" Monod, 11 , a theme that he promises to develop in later chapters.
The last general property Monod offers up as distinguishing living organisms is reproductive invariance which is the ability of a living being to reproduce and transmit the information corresponding to their own highly ordered structure.
The author defines the primary telonomic project "as consisting in the transmission from generation to generation of the invariance content characteristic of the species" Monod, 14 the preservation and multiplication of the species. Monod later retracts autonomous morphogenesis spontaneous structuration as a property of living beings and says instead that it should be thought of as "mechanism" leaving two essential properties of living beings: reproductive invariance and structural teleonomy.
He then brings up and defends against a possible thermodynamic objection to reproductive invariance and points out the extreme efficiency of the teleonomic apparatus in accomplishing the preservation and reproduction of the structure. Here the author restates that nature is objective and does not pursue an end or have a purpose and he points out an apparent "epistemological [the study of the origin, nature, methods, and limits of human knowledge] contradiction" between the teleonomic character of living organisms and the principle of objectivity.
With that cliffhanger of internal intellectual struggle Monod ends chapter one. Vitalisms and animisms In chapter two "Vitalisms and Animisms" Monod states that invariance must have preceded teleonomy, a conclusion reached by the Darwinian idea that teleonomic structures are due to variations in structures that already had the property of invariance and could therefore preserve the effects of chance mutations.
He offers the selective theory as being consistent with the postulate of objectivity and allowing for epistemological coherence. The author then says that in the rest of the chapter he will address religious ideologies and philosophical systems that assume the reverse hypothesis: that invariance developed out of an initial teleonomic principle this defies the principle of objectivity. Monod admits he is more interested in animism and will therefore devote more analysis to it.
He briefly discuses the murky metaphysical vitalism of Henri Bergson and then discusses the scientific vitalism of Elsasser and Polanyi which contend that physical forces and chemical interactions that have been studied in non-living matter do not fully account for invariance and teleonomy and therefore other "biotonic laws" are at work in living matter. The author points out that the scientific vitalist argument lacks support and that it draws its justification not from knowledge or observations but from our present day lack of knowledge.
He goes on to point out that today the mechanism of invariance is sufficiently understood to the point that no non-physical principle "biotonic law" is needed for its interpretation. Monod next points out that our ancestors had a history of animating objects by giving spirits to them so as to bridge the apparent gap between the living and non-living. To them a being made sense and was understandable only through the purpose animating the being and so if mysterious objects, such as rocks, rivers, rain, and stars, exist it must also be for a purpose essentially there are no inanimate objects to them.
Nature is explained with the same conscious and purposive manner as human activity. Monod points out that this animist line of thought is still present in philosophy that makes no essential distinction between matter and life and frames biological evolution as a component of cosmic evolution evolutive force operating throughout the entire universe. He contends that these lines of thought abandon the postulate of objectivity and also contain the anthropocentric illusion. At the end of this chapter Monod states that the thesis he "shall present in this book is that the biosphere does not contain a predictable class of objects or of events but constitutes a particular occurrence, compatible indeed with first principles, but not deducible from those principles and therefore essentially unpredictable" Monod, In his view the biosphere is unpredictable for the same reason that the particular configuration of atoms in a pebble are unpredictable.
He then points out that society is willing to accept a universal theory that is compatible with but does not foresee the particular configuration of atoms in a pebble but it is a different story when it comes to humans; "We would like to think ourselves necessary, inevitable, ordained from all eternity.
All religions, nearly all philosophies, and even a part of science testify to the unwearying, heroic effort of mankind desperately denying its own contingency" Monod, It is this contingency of human existence that is the central message of Chance and Necessity; that life arose by chance and all beings of life, including humans, are the products of natural selection. It starts off by stating that proteins are the molecular agents of teleonomic performance in living beings.
Monod continues by writing that living beings are chemical machines, every organism constitutes a coherent and functional unit, and that the organism is a self-constructing machine whose macroscopic structure is not determined by outside forces but by autonomous internal interactions. The author spends much of the chapter reviewing general facts of biochemistry. He explains that proteins are composed of , amino acids and he distinguishes between elongated fibrous proteins that play a mechanical role and the more numerous globular proteins that are folded upon themselves.
He talks about the extraordinary specificity of action that enzymes display as exemplified by their ability to not only recognize a specific geometric isomer but an optical isomer as well. He points out that enzymes are optically active themselves, L isomers are the "natural" isomers, and that the specificity of action and the sterospecificity of the reaction conducted by an enzyme are the result of the positioning of the molecules with respect to each other.
Monod writes that an enzymatic reaction can be seen in two steps: The formation of a sterospecific complex between protein and substrate and the catalytic activation of a reaction within the complex he stresses again that the reaction is oriented and specified by the structure of the complex. He next considers the energetic differences between covalent and non-covalent bonds and how the speed of a reaction is affected by activation energy.
Since the activation energy of a covalent bond is high the reaction will have a slower speed than that of a non-covalent bond which occurs spontaneously and rapidly. The author points out that non-covalent interactions attain stability only through numerous interactions and when applied over short distances. To attain stable non-covalent interaction there is a need for complementary sites between two interacting molecules so as to permit several atoms of the one to enter into contact with several atoms of the other.
In this complex the molecule of substrate is strictly positioned by the multiple non-covalent interactions with the enzyme. Enzymatic catalysis is believed to result from the inductive and polarizing action of certain chemical groupings of the specific receptor. Monod reminds us that this reaction comes at the expense of chemical potential energy.
Microscopic cybernetics In chapter four "Microscopic Cybernetics" the author starts out by repeating the characteristic of extreme specificity of enzymes and the extreme efficiency of the chemical machinery in living organisms. The rest of the chapter is a discussion of the principles that cell metabolism works by. Monod first brings up allosteric enzymes that are capable of recognizing compounds other than a substrate whose association with the enzyme protein has a modifying effect of heightening or inhibiting the enzyme activity with respect to the substrate.
Monod lists and defines four regulatory patterns. The first is feedback inhibition. Feedback activation is when the enzyme is activated by a product of degradation of the terminal metabolite.
Parallel activation takes place when the first enzyme of a metabolic sequence is activated by a metabolite synthesized by an independent parallel sequence. Activation through a precursor is defined as when an enzyme is activated by a precursor of its substrate and a particularly frequent case of this is activation of the enzyme by the substrate itself. Allosteric enzymes are usually under the simultaneous control of several allosteric effectors. Next Monod makes reference to his own research and talks about the S shaped non-linear curve that is characteristic of allosteric enzymes when activity is plotted against concentration of an effector including the substrate.
Allosteric interactions are mediated by discrete shifts in the proteins structure and this allows certain proteins to assume different conformational states. Cooperative and antagonistic interactions of ligands are indirect: ligands interact with the protein not with other ligands.
Allosteric proteins are oligomeric made up of identical protomer subunits and each protomer has a receptor for each of the ligands. As a consequence of protomer assembly each subunit is constrained by its neighbor. Upon dissociation each protomer can assume a relaxed state and this concerted response of each protomer accounts for the nonlinearity of enzyme activity: a ligand molecule that stabilizes the relaxed state of one of the monomers prevents the others from returning to the associated state.
These simple molecular mechanisms account for the integrative properties of allosteric enzymes. Monod again references his own work as he talks about the lactose system consisting of three proteins in Escherica coli. He explains that galactoside permease one of the proteins in the lactose system enables the galactoside sugars to penetrate and accumulate within the cell. When Escherica coli are grown in a medium with no galactosides the three proteins are synthesized very slowly about one molecule every five generations.
About two minutes after adding a galactoside inducer the rate of synthesis of the three proteins increases a thousandfold. Monod explains that the rate of mRNA synthesis from the lactose operon determines the rate of the proteins synthesis.
He lists the components of the regulatory system as i, the regulator gene that directs constant synthesis of the repressor protein R , o, the operator segment of DNA that the repressor specifically recognizes and forms a stable complex with, and p, the DNA promoter where RNA polymerase binds. Synthesis of mRNA is blocked when the repressor is bound to the operator.
When the repressor is in the free state it is able to recognize and bind beta galactosides thus dissociating the operator repressor complex and permitting synthesis of the mRNA and protein. Monod spends some time stressing that there need be no chemical relationship between a substrate and an allosteric ligand and it is this "gratuity" that has allowed molecular evolution to make a huge network of interconnections and make each organism an autonomous functional unit.
In the last part of the chapter Monod criticizes "holists" who challenge the value to analytically complex systems such as living organisms and that complex systems cannot be reduced to the sum of their parts.
Monod first gives an example of dissecting a computer and then points out how teleonomic performances can be seen on a molecular level. He also states that the complexity of the cybernetic network in living beings is far too complex to study by the overall behavior of whole organisms.
Molecular ontogeny At the start of chapter five "Molecular Ontogenesis" Monod states he will show that the process of spontaneous autonomous morphogenesis depends upon "the sterospecific recognition properties of proteins; that it is primarily a microscopic process before manifesting itself in macroscopic structures.
Monod mentions oligomeric globular proteins again and how they appear in aggregates containing geometrically equivalent protomer subunits associated into a non-covalent steric complex. With mild treatment protomers are separated and the oligomer protein loses function but if the initial "normal" conditions are restored the subunits will usually reassemble spontaneously. This spontaneity is due to the fact that the chemical potential needed to form the oligomer is present in the solution of monomers and because the bonds formed are non-covalent.
The author continues to mention the sterospecific, spontaneous assembly of ribosomes and T4 bacteriophage from their protein constituents in vitro. Next Monod reviews the primary and tertiary structure of proteins. In reviewing the tertiary structure, what he calls the native shape, he talks about the non-covalent interactions which bind the amino acids and the folding that determines the molecules three-dimensional shape including the sterospecific binding site.
The author then writes that a primary structure exists in a single or a small number of related states, as is the case with allosteric proteins precisely defined conformational native state under normal physiological conditions. Prior to folding there is no biological activity. The sequence of the amino acid residues and the initial conditions determine the protein folding and therefore dictate the function. Monod splits up organism development into four broad stages: First the folding of the polypeptide sequence into globular proteins, then the association between proteins into organelles, thirdly the interactions between cells that make up tissue and organs, and lastly "coordination and differentiation of chemical activities via allosteric-type interactions" Monod, Each stage is more highly ordered and results from spontaneous interactions between products of the previous stage and the initial source is the genetic information represented by the polypeptide sequences.
The author then spends some time developing the fact that the preceding sequence of amino acids had no bearing on what the next amino acid will be. He says this "random" message seems to be composed haphazardly from a random origin and he ends the chapter poetically when he writes "Randomness caught on the wing, preserved, reproduced by the machinery of invariance and thus converted into order, rule, and necessity.
El azar y la necesidad
Milabar Synthesis necesjdad mRNA is blocked when the repressor is bound to the operator. Prepared sluggishness sometimes while doing between apps Get the ServiceUI. Descargar gratis el libro la rebelion de las ratas DownloadDescargar gratis el libro la rebelion de las ratas. He contends that these lines of thought abandon the postulate of objectivity and also contain the anthropocentric illusion. He says necesivad the important message of science is that in the defining el azar y la necesidad jacques monod a new source of truth which demands revision of ethical premises and a total break with the animist tradition.
El Azar y la Necesidad
EL AZAR Y LA NECESIDAD