Acid nucleic và nguồn gốc sự sống

ACID NUCLEIC VÀ NGUỒN GỐC SỰ SỐNG1NUCLEIC ACIDSTwo classes of nucleic acids are found in cellsDeoxyribonucleic acidDNARibonucleic acidRNAMany of the functions of these nucleic acids are related or overlapping2NUCLEIC ACIDSDNAPolymer of deoxynucleotidesGenetic material of all cellular life and of some virusesOrganized into “genes”Blueprints for proteinsRNAPolymer of nucleotidesGenetic material of some virusesIntermediates in gene expressionRibosome componentsSome possess enzyme-like activity“Ribozymes”3(DEOXY)RIBONUCLEOTIDESNucleic acids are polymersDNA monomers are deoxyribonucleotidesRNA monomers are ribonucleotides4(DEOXY)RIBONUCLEOTIDESNucleic acid monomers consist of three partsSugarNitrogenous basePhosphate group(s)These three parts are assembled by condensation reactions5(DEOXY)RIBONUCLEOTIDESBoth DNA and RNA possess a pentose sugarRibose in RNADeoxyribose in DNALacks the 2’ OH group possessed by ribose6(DEOXY)RIBONUCLEOTIDESBoth DNA and RNA possess four nitrogenous basesGuanineAdenineCytosineThymine (in DNA)Uracil (in RNA)7(DEOXY)RIBONUCLEOTIDESOne or more phosphate groups are attached to the 5’ carbon of (deoxy)riboseTriphosphates used in polynucleotide synthesisOnly one is incorporated into a DNA or RNA chain8(DEOXY)RIBONUCLEOTIDESSome ribonucleotides have additional functionse.g., ATP is involved in energy transfers within cells9POLYNUCLEOTIDESNucleotides are joined via condensation reactions3’ OH and 5’ phosphate OHNew nucleotides are added to the 3’ end of growing chainTwo strands of double-stranded polynucleotides are NOT covalently linkedInteract through H-bonds10POLYNUCLEOTIDESStructure of a single strand of DNA or RNABackbone of alternating sugar and phosphate groupsNitrogenous bases projecting from this backbone11POLYNUCLEOTIDESMost DNA and some RNA is double-strandedBases project from the sugar-phosphate backboneBases of two strands interact through H-bonds12POLYNUCLEOTIDESDNA is organized into units called genesA gene is a blueprint for a proteinRNA is an intermediate in gene expressionDNA  RNA  protein13ORIGIN OF LIFELife on Earth initially arose amidst a sea of various biological moleculese.g., Amino acids, sugars, purines, ATP, etc.The production and accumulation of these biological molecules preceded the origin of life on Earth14ORIGIN OF LIFEStanley Miller and Harold Urey recreated the assumed early atmosphere (1953)Contained H2O, H2, CH4, and NH3Lacked free O2Energy input in forms of heat and electrical sparksMimic geothermal heat and lightning15ORIGIN OF LIFEThe initial Miller-Urey experiment and various similar experiments succeeded in producing:All 20 amino acidsSeveral sugarsLipidsPurines and pyrimidinesATP (when phosphate was added)etc.16ORIGIN OF LIFEThe atmosphere replicated in these experiments likely differed from the earth’s early atmosphereAtmosphere likely possessed little or no O2Atmosphere likely possessed more CO, CO2, and N2 than that in Miller’s experimentStill, the Miller-Urey experiment did demonstrate that key organic molecules critical to life could be produced abiotically from inorganic precursors17ORIGIN OF LIFEOther researchers have used combinations of gases based on our current understanding of Earth’s early atmosphereSimilar results were achievedOrganic molecules can be abiotically produced in an atmosphere composed primarily of H2O, CO, CO2, and N218REFERENCESCampbell, Neil A. and Reese, Jane B. Biology, 7th edition. Pearson Education, Inc. 2005.Campbell, Neil A., Reese, Jane B., Taylor, Martha R., and Simon, Eric J. Biology, Concepts and Connections, 5th edition. Pearson Education, Inc. 2006.Nester, Eugene W., Anderson, Denise G., Roberts, C. Evans Jr., and Nester, Martha T. Microbiology, A Human Perspective, 5th edition. McGraw-Hill Companies, Inc. 2007.Limson, Janice. 2002.