abiotic synthesis of organic monomers and polymers pdf

Abiotic synthesis of organic monomers and polymers pdf

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1. Introduction


A5. Abiotic Synthesis of Genetic Polymers

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He hypothesized that this mixture resembled the atmosphere of the early earth. The mixture was kept circulating by continuously boiling and then condensing the water.

At the end of a week, Miller used paper chromatography to show that the flask now contained several amino acids as well as some other organic molecules. However, it is now thought that the atmosphere of the early earth was not rich in methane and ammonia — essential ingredients in Miller's experiments. The question is: were these molecules simply terrestrial contaminants that got into the meteorite after it fell to earth? Live bacteria could easily survive such a trip.

Whether or not the molecules that formed terrestrial life arrived here from space, there is little doubt that organic matter continuously rains down on the earth estimated at 30 tons per day. They achieved this by bombarding a mixture of formamide and clay with powerful laser pulses that mimicked the temperature and pressure expected when a large meteorite strikes the earth.

Formamide is a simple substance, CH 3 NO, thought to have been abundant on the early earth and containing the four elements fundamental to all life. Another problem is how polymers — the basis of life itself — could be assembled. While no ribozyme in nature has yet been found that can replicate itself, ribozymes have been synthesized in the laboratory that can catalyze the assembly of short oligonucleotides into exact complements of themselves.

The ribozyme serves as both. To function, the machinery of life must be separated from its surroundings — some form of extracellular fluid ECF. This function is provided by the plasma membrane. Today's plasma membranes are made of a double layer of phospholipids.

Specialized transmembrane transporters are needed for ions, hydrophilic , and charged organic molecules e. However, the same Szostak lab that produced the finding described above reported in the 3 July issue of Nature that fatty acids , fatty alcohols , and monoglycerides — all molecules that can be synthesized under prebiotic conditions — can also form lipid bilayers and these can spontaneously assemble into enclosed vesicles.

These workers loaded their synthetic vesicles with a short single strand of deoxycytidine dC structured to provide a template for its replication. When the vesicles were placed in a medium containing chemically modified dG, these nucleotides entered the vesicles and assembled into a strand of Gs complementary to the template strand of Cs. Here, then, is a simple system that is a plausible model for the creation of the first cells from the primeval "soup" of organic molecules.

Several colonial flagellated green algae provide a clue. These species are called colonial because they are made up simply of clusters of independent cells. If a single cell of Gonium , Pandorina , or Eudorina is isolated from the rest of the colony, it will swim away looking quite like a Chlamydomonas cell.

Then, as it undergoes mitosis, it will form a new colony with the characteristic number of cells in that colony. The figures are not drawn to scale.

The situation in Pleodorina and Volvox is different. In these organisms, some of the cells of the colony most in Volvox are not able to live independently. If a nonreproductive cell is isolated from a Volvox colony, it will fail to reproduce itself by mitosis and eventually will die. What has happened?

In some way, as yet unclear, Volvox has crossed the line separating simple colonial organisms from truly multicellular ones. Unlike Gonium , Volvox cannot be considered simply a colony of individual cells. It is a single organism whose cells have lost their ability to live independently. If a sufficient number of them become damaged, the entire sphere of cells will die. What has Volvox gained? In giving up their independence, the cells of Volvox have become specialists. No longer does every cell carry out all of life's functions as in colonial forms ; instead certain cells specialize to carry out certain functions while leaving other functions to other specialists.

In Volvox this process goes no further than having certain cells specialize for reproduction while others, unable to reproduce themselves, fulfill the needs for photosynthesis and locomotion. In more complex multicellular organisms, the degree of specialization is carried much further. Each cell has one or two precise functions to carry out. It depends on other cells to carry out all the other functions needed to maintain the life of the organism and thus its own. The specialization and division of labor among cells is the outcome of their history of differentiation.

One of the great problems in biology is how differentiation arises among cells, all of which having arisen by mitosis, share the same genes.

Link to a discussion of the solution. The genomes of both Chlamydomonas and Volvox have been sequenced. Although one is unicellular, the other multicellular, they have not only about the same number of protein-encoding genes 14, in Chlamydomonas , 14, in Volvox but most of these are homologous.

Volvox has only 58 genes that have no relatives in Chlamydomonas and even fewer unique mRNAs. How to explain this apparent paradox? My guess is that just as we have seen in the evolution of animals [ Examples ], we are seeing here that the evolution of organismic complexity is not so much a matter of the evolution of new genes but rather the evolution of changes in the control elements promoters and enhancers that dictate how and where the basic tool kit of eukaryotic genes will be expressed.

The evidence is compelling that all these organisms are close relatives; that is, belong to the same clade. They illustrate how colonial forms could arise from unicellular ones and multicellular forms from colonial ones.

When I headed off to college in , I wrote an essay speculating on the possibility that some day we would be able to create a living organism from nonliving ingredients. By the time I finished my formal studies in biology — having learned of the incredible complexity of even the simplest organism — I concluded that such a feat could never be accomplished.

Several recent advances suggest that we may be getting close to creating life. But note that these examples represent laboratory manipulations that do not necessarily reflect what may have happened when life first appeared. In , scientists at the J. Craig Venter Institute JCVI reported in Science 29 February that they had succeeded in synthesizing a complete bacterial chromosome — containing , base pairs — starting from single deoxynucleotides.

The entire sequence of the genome of Mycoplasma genitalium was already known [ Link ]. Using this information, they synthesized some 10, short oligonucleotides each about 50 bp long representing the entire genitalium genome and then — step by step — assembled these into longer and longer fragments until finally they had made the entire circular DNA molecule that is the genome.

The same team showed in the previous year see Science 3 August that they could insert an entire chromosome from one species of mycoplasma into the cytoplasm of a related species and, in due course, the recipient lost its own chromosome perhaps destroyed by restriction enzymes encoded by the donor chromosome and began expressing the phenotype of the donor.

In short, they had changed one species into another. But the donor chromosome was made by the donor bacterium, not synthesized in the laboratory. However, there should be no serious obstacle to achieving the same genome transplantation with a chemically-synthesized chromosome. They've done it! The same team reported on 20 May in the online Science Express that they had successfully transplanted a completely synthetic genome — based on that of Mycoplasma mycoides — into the related species Mycoplasma capricolum.

The recipient strain grew well and soon acquired the phenotype of the M. In the 4 April issue of Science Annaluru, N. In the 10 March issue of Science , the same team now reports the synthesis of five more yeast chromosome as well as an additional half chromosome. Each of these works when it replaces the wild-type chromosome. Remarkably, even when substituting 2 or 3 of their synthetic chromosomes in a single cell, the cell remains viable carrying out its normal functions.

Abiotic Synthesis of Organic Molecules 1. Miller's Experiment 2. Molecules from outer space? Deep-Sea Hydrothermal Vents 4. The First Cell? Creating Life? Link to a discussion of the possibility of life on Mars and more on the ALH meteorite.

1. Introduction

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He hypothesized that this mixture resembled the atmosphere of the early earth. The mixture was kept circulating by continuously boiling and then condensing the water. At the end of a week, Miller used paper chromatography to show that the flask now contained several amino acids as well as some other organic molecules. However, it is now thought that the atmosphere of the early earth was not rich in methane and ammonia — essential ingredients in Miller's experiments. The question is: were these molecules simply terrestrial contaminants that got into the meteorite after it fell to earth?


Metrics details. How life on Earth began remains an unexplained scientific problem. This problem is nuanced in its practical details and the way attempted explanations feedback with questions and developments in other areas of science, including astronomy, biology, and planetary science. Prebiotic chemistry attempts to address this issue theoretically, experimentally, and observationally.

Keeping in mind the importance of amphiphilic lipids for the formation of semipermeable membranes, a review summary of the sources of appropriate precursors, and chemical reactions for the abiotic synthesis of lipids is presented here within the framework of the theory of chemical evolution. It covers the presence in different cosmic environments of precursors for the formation of the biochemical molecules necessary for the emergence of life on Earth. It starts 1 with a short introduction. Then the following matters are briefly reviewed: 2 The circumstellar and interstellar molecules, some of which, could generate straight chain fatty acids through C 9.

In evolutionary biology , abiogenesis , or informally the origin of life OoL , [3] [4] [5] [a] is the natural process by which life has arisen from non-living matter, such as simple organic compounds. There are several principles and hypotheses for how abiogenesis could have occurred. The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. Life functions through the specialized chemistry of carbon and water and builds largely upon four key families of chemicals: lipids cell membranes , carbohydrates sugars, cellulose , amino acids protein metabolism , and nucleic acids DNA and RNA. Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules.

A5. Abiotic Synthesis of Genetic Polymers

These genetic polymers have one property that at first glance seems not conducive to a genetic molecule. Both are polyanions, which must be packed into a cell and folded onto itself to form the classic dsDNA helix and many different RNA structures. This problem is solved to some degree by the presence of counterions that help mask the charge on the negative backbone of the nucleic acids. The presence of phosphate in the phospodiester backbone linkage does confer an important advantage over other possible links carboxylic acid esters, amides and anhydrides. The electrophilic phosphorous atom is hindered from nucleophilic attack by the negative O attached to the phosphorous.

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