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Transcript
Characterization of Extrasolar Planets What Life? R.U. Claudi Intrusion in the Biology Habitability around the Sun and the other stars Search for life Operative definition for Life A system is alive if it: -contains informations -exchanges energy with the environment - can to breed -is subject to random variation of its information baggage To Continue the generalization… Physical structures based on solid physics and the electronics of liquid crystal… …with habitat that could be both rocky planets with Tsup 200 250 K, or asteroids… …but it is difficult to imagin a natural process that can generate them … …or System based on the electromagnetic plasma … http://www.cv.nrao.edu/~awootten/allmols.html …for which the habitability is given by the interstellar medium condition Carbon based Chemistry …. it easy oxidizes itself: CO2 it easy reduces itself: CH4 100% 100% 100% 100% 100% 100% 100% 94% 89% 29% 81% But expecially it can combine itself with other atoms in order to make coplex molecules http://www.cv.nrao.edu/~awootten/allmols.html … in acqueous solution Evolution Chemical Reactions Solution Solid Liquid Too Slow Alcohol Hydrocarbons NH3 CH4 Water Why water?: characteristics ε=80 it allows the salts dissociation Capacity to build H bonds with dissolved molecules It is an optimum thermal mediator water remain in liquid phase in a large temperature range Common Ice has a lower density that water Alternative Liquid Solvents T fusion C -182.0 T boiling C -164.0 C 2H 6 -183.0 -88.6 Methanol CH3OH -97.0 64.7 Ethyl CH3CH2OH -114.0 78.3 Ammonia NH3 -77.7 Hydrocarbons Methan Ethan CH4 Alcohols -33.3 they are characterized by a low value of the dielectric constant, in some cases they do not make H bonds with solutes, in other cases they attack the organic material (e.g. ammonia) …in other words: Living system based on carbon chemestry that exploits water as solvent for chemical reaction… DOES IT REMEMBER SOMETHING? Physical structures based on chemestry and organized in linear macro molecules Acido Peptico Nucleico (PNA) p-RNA Palad PaladThy Bibl.:Maurel M.C., 1999 Organic compounds of living beeing Structural Elements Proteins Carbohyidrates Enzymes Transmission of signal in to the cell Energy provision Lipids Nucleic Acids Provision and transfer of information Proteins and Amino acids • Proteins are made by molecular chains known as amino acids • Proteins are made by chains with 14500 amino acids, but they could reach 30000 amino acids. • Only 20 amino acids (in nature there are more). • All of them have L chirality, only the Glycine has D chirality) Carboxyl group: COOH O O H Glycine N H O C C H O H N H C H H C C C H N H H Amine Group: NH2 L-Alanine H O C C O H H C D-Alanine H H alanine H Peptide link H N H O H H O C C N C C H H H H O H C H H O H H N H H C H H glycine O H C Central carbon atom H O H Alanine H H The 20 amino acids Alanine Glutamic A. Leucine Serine Arginine Glutamine Lysine Threonine Asparagine Glycine Methionine Tryptophan Aspartic A. Histidine Phenylalaline Tyrosine Cysteine Isoleucine Proline Valine desossiribonucleic Acid (DNA) 1 sugar (deoxyribose) nucleotide 1 phosphate group 1 Nitrogenous base Pyrimidine Purine Dimension of the DNA Super Helix …and protein synthesis no information formation Transcription Decoding Correspondance between amino acids and triples Start: AUG (in m-RNA) Stop: UAA; UAG,UGA (in m-RNA) Energy retrieval Chemical Energy available for the cell upon the break of phosphoric bonds due to enzymatic hydrolysis ATP: Adenosine triphosphate N H2 High energy bonds: 30 kJ/mol N N Adenosine O O O O P~ O P ~O P O O O N N O Ribose O CH2 OH + OH Energetic Process Three main process: Photosynthesys: Energetic process that save energy Glucose Oxidation: Fermentation: Ethanol Bio chemical Process that release energy SOMETIMES LIFE IS A HARD JOB Aerobic Batterium that obtain the necessary energy by the iron and sulfur oxidation Ph 1.3-4.5 T 30-35 C Dimension Thiobacillus Ferrooxidans 1.0 m Evidence of a common ancestor •All the living beeings exploit DNA, RNA, proteins, sugars and lipids •Could be created only one hierarchy of species of continuos complexity •Similar Organisms from a biological point of view share the most part of DNA •Common ancestor means transitional fossils •Primordial limb and organs like, e.g., the wings of penguins Phylogenetic Tree and common ancestor procaryote Eucariote Metanococcus CO2, H2, T 50°-86° Alobacterium 5M/Litro di NaCl • ESTREMOPHILES Archaea Sulfolobus Ph 1-5, T 65°-90° Strain-121 T 121° (14/8/2003) Pre-Cambrian Life Procaryotes Iron formation Free oxigen accumulation Eucaryotes multicelluar life CO2 O2 CO2 O2 Animals molluscs Humans Crust Formation Plants and flowers 4 Gya 3 Gya 2 Gya 1 Gya Dinosaurs and Birds Trilobites Cambrian Explosion Three lines of evidence… …that life existed 3.85 Gya and that it was constituted by unicellular beeing 1. Stromatolites Finding 2. micro fossils Finding 3. 12C enrichment in the fossil organisms Origin of life: Ancient fossils •Most Acient fossils have 3.5 Gy and they have been found at Apex Chert in West Australia and South Africa •Evidence of organic material formation up to 3.5 Gya in the ISUA formation in Greenland •Stromatolites with 3.5 Gy of age in Australia Cambrian Explosion •Small fossil shells (1-5 mm) •Shells, skeletons and teeth lead towards an evolutive explosion of specie •In 35 My all the modern species pop up •Osseous and hard parts of bodies let grow uo the fossil number (Cambrian Explosion) Orgin of life: Urey-Miller Experiment After a week 15% of carbon transform itself in organic compounds. 2% in amino acids (Glycine, α-alanine and βalanine) •Critiques: –Primeval Atmosphere was not strongly reducer, not so much! –UV Radiation role? –Both chiralities are present with the same abbunndance Origin of Life: Thermal Vents The necessary energy to the life chemistry could be taken by the geothermal heat. Water protects by the UV radiation Water emitted at 450 C Estremophiles, e.g.: Strain 121 Water warmed up to 1000C Origin of life: panspermia •Amino acids have been found in space (amino acid precursors found in molecular clouds, glycine in Sagitarius B2). •Excess of diversity of L chirality amino acids found in the Murchison meteorite (Boatta, 2002) • Amino acids production in laboratory from spatial ice once it is UV irradiated (“Nature 416”, 28 Mar 2002). Murchison’s Meteorite Conclusions •A living system is the result of a slow evolution process due to the sum of several events with plausible probability •As soon as the environment becom “Habitable” life start to generate •The living system based on the carbon chemistry and on water is the most probable •On Earth the information encoding and decoding system is based on DNA and RNA, but we saw that could exists other system for information supply…