OriginofLife “Know then thyself , presume not GOD to scan … The proper study of mankind is MAN…” Biochemistry Project 1 by Imran * Jimmy * Lingareddy
Introduction What does life need? A miracle? “Time-Line” For the Origin of Life The major View points Spontaneous formation of organic molecules “RNA” world Metabolic View
What does life need? A way of harnessing energy to do useful work, a way of storing and reproducing genetic information, a way to keep the inside separated from the outside.
Molecules of life : In order to understand life we need to understand the chemistry of life. There are 4 major classifications :
Nucleic Acid Lipids Carbohydrates Proteins
A Miracle? Francis Crick was the co-discover of the DNA molecule. Crick received a Nobel price for discovering the structure of DNA. He said this about the formation of life: “The origin of life appears at the moment to be almost a miracle.”
The major view points Among the many theories of the origin of life, three major viewpoints have been identiﬁed: Spontaneous formation of organic molecules “RNA” world Metabolic View
Spontaneous formation of organic molecules Stanley Miller and Harold Urey (1953) attempted to reproduce conditions at the ocean’s edge under a reducing atmosphere. The primordial Earth was a very different place than today, with greater amounts of energy, stronger storms, etc. The oceans were a "soup" of organic compounds that were formed by inorganic processes. Miller's (and subsequent) experiments have proved that life originated in a different way, over 3 billion years ago. He placed simple inorganic molecules into his apparatus to produce a variety of complex molecules:
Spontaneous formation (continued) In subsequent experiments, nucleic acids were detected; a likely scheme for their formation is from polymerization of cyanide (which can be readily formed in a primitive atmosphere) Tetramer can be rearranged to form
Spontaneous formation (continued) The nitrogen bases of the nucleotides are broadly divided into two groups mainly: purines and pyrimidines based on the type of cyclic ring present in the base. Purines Adenine (A) or 6-aminopurine Guanine (G) or 2-amino,6-oxypurine Pyrimidines: Cytosine (C) or 6-amino,2-oxy pyrimidine Thymine (T) or 2,6-oxy,5-methyl pyrimidine Miller’s experiment only produce Adenine.
RNA World There was a stage in the development of life with nothing but self-replicating RNA molecules. It is assumed that RNA acted as a precursor of both protein and DNA, in the sense that it can serve both as catalyst (like protein enzymes) and as carrier of genetic information. Proteins, DNA, and cell membranes added later in this scenario.
RNA World (Continued) Jack Szostak, American biologist was awarded the 2009 Nobel Prize for the discovery of how chromosomes are protected by telomeres. He has shown that certain catalytic RNAs can, indeed, join smaller RNA sequences together, hinting at the potential for self-replication. Given the right starting conditions, such a self-replicating RNA might increase its number at the expense of the "lifeless" ones surrounding it.
RNA World (Continued) Lets watch a video about Jack Szostak’s discoveries
RNA World (Continued) Where did the first RNA come from? The first RNA polymers may have formed on clay templates as clay molecules have very regular structures James Ferris, Professor of Chemistry at Rensselaer Polytechnic Institute, has discovered that the building blocks of RNA polymer were linked together on the surface of a common clay, montmorillonite.
RNA World (Continued) There are still some open questions about the RNA World to act as an ultimate origin of life. The RNA system is too complex to have arisen without synthesis by a genetic precursor or prior enzyme-less metabolism. There are now good leads for simple, spontaneous processes to initiate on the early Earth for the synthesis of nucleotides.
Metabolic View One of the key ideas advanced by Wächtershäuser is that an early form of metabolism predated genetics. Metabolism here means a cycle of chemical reactions that produce energy in a form that can be harnessed by other processes. The idea is that once a primitive metabolic cycle was established, it began to produce ever more complex compounds. The Miller-Urey experiment explained before was an experiment that simulated hypothetical conditions present on the early Earth and tested for the occurrence of chemical evolution.
Metabolic View (continued) This metabolism-first model has a strong champion in Harold Morowitz, who paints the two major models for life's origin as "heaven and hell” and found the probability of creation of single bacterium. Ferric citrate is a structure formed from the transition metal iron and citrate, a compound produced by plants, algae, and many bacteria. Morowitz propose that structures like this could have catalyzed the formation of molecular building blocks, leading ultimately to the formation of complex molecules essential for the origin of life.
Metabolic View (continued) A totally new and highly controversial theory on the origin of life on earth, is set to cause a storm in the science world and has implications for the existence of life on other planets. Research by Professor William Martin of the University of Dusseldorf and Dr Michael Russell of the Scottish Environmental Research Centre in Glasgow, claims that living systems originated from inorganic incubators – small compartments in iron sulphide rocks.
Metabolic View (continued) As hydrothermal fluid - rich in compounds such as hydrogen, cyanide, sulphides and carbon monoxide - emerged from the earth's crust at the ocean floor, it reacted inside the tiny metal sulphide cavities. They provided the right microenvironment for chemical reactions to take place. The iron sulphide cells, is where life began.
Metabolic View (continued) Mike Russell’s designed an appartus which will recreate the first moments of life on Earth, and give experimental support to the metabolic view. He hopes to reproduce life’s first steps, by reacting the carbon dioxide in the ‘ocean’ water with the hydrogen in the ‘spring’ water to make the simple organic molecules methane and acetate. Russell thinks that if his reactor produces just about anything from tar to E. coli it will have been worthwhile "recreating the origins of life"
Acknowledgements http://www.reuters.com/article/idUSN2323973520070523 http://www.spaceref.com/news/viewnews.html?id=1079 http://rpi.edu/dept/chem/chem_faculty/profiles/ferris.html http://www.spaceref.com/news/viewnews.html?id=1079 Evolution of the first metabolic cycles, Proc. Natl. Acad. Sci. USA, Vol. 87, pp. 200-204, January 1990 http://www.internetchemie.info/news/2010/sep10/origin-of-life.html http://blogs.discovermagazine.com/cosmicvariance/files/2010/03/Whitfield-Nascence-man.pdf http://www.spaceref.com/news/viewnews.html?id=1079 http://www.spaceref.com/news/viewnews.html?id=1079