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22-AUGUST-2008 06:13:22 - dating This article has multiple issues. Please help improve the article or discuss these issues on the talk page. It does not cite any references or sources. Please help improve it by citing reliable sources. Tagged since March 2007. Its introduction provides insufficient context for those unfamiliar with the subject. Tagged since August 2007. It may require general cleanup to meet 's quality standards. Tagged since March 2007. Amino acid dating is a technique used to estimate age in a wide variety of situations. This technique relates changes in amino acid molecules to the time elapsed since they were formed. This technique is used in paleobiology, archaeology, forensic science, and numerous other fields. Contents 1 Racemization chemistry 2 Amino acids in living organisms 3 Factors affecting racemization 4 Amino acids used 5 Applications 6 Non-biological applications 7 Procedure 8 External links Racemization chemistry Most amino acid molecules possess an asymmetric carbon atom or two which can occupy either of two positions like a toggle switch and still be tightly bound to its neighbors. These positions are characterized as D right, or L left, according to which way the molecule bends plane polarized light. This is a common phenomenon throughout biochemistry. Left to themselves, over time the ratio of D/L molecules will roughly even out. This process of conversion is known as racemization. Amino acids in living organisms Life requires a certain composition AND shape of amino acid molecules in order to complete their function. Living organisms on earth keep their amino acids in the L position, with a notable exception found in certain bacterial cell walls, and their sugars in the D position. When the organism dies, control ceases, and the ratio of D/L moves slowly toward equilibrium racemic. Thus, measuring the ratio of D/L of a sample can allow calculations of how long ago the specimen died. Factors affecting racemization The rate at which racemization proceeds depends upon the type of amino acid, average temperature, humidity, acidity, alkalinity, and enclosing matrix. Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization. These effects restrict amino acid chronologies to materials with known environmental histories and/or relative intercomparisons with other dating methods. Temperature and humidity histories of microenvironments are being produced at ever increasing rates as technologies advance and technologists accumulate data. These are important to amino acid dating because racemization occurs much faster in warm, wet conditions compared to cold, dry conditions. Temperate to cold region studies are much more common than tropical studies, and the steady cold of the ocean floor or the dry interior of bones and shells have contributed most to the accumulation of racemization dating data. Strong acidity and mild to strong alkalinity induce greatly increased racemization rates. Generally, they are not assumed to have a great impact in the natural environment, though tephrochronological data may shed new light on this variable. The enclosing matrix is probably the most difficult variable in amino acid dating. This includes racemization rate variation among species and organs, and is affected by the depth of decomposition, porosity, and catalytic effects of local metals and minerals. Amino acids used Asparagine acidified to aspartic acid racemizes quickly and has frequently been used to date materials from the present back to around 25000 BP. Isoleucine racemizes much more slowly, and has been used to date materials from 5000 to 2 million years of age. Concentration thresholds and less comprehensive environmental histories produce much greater margins of error with older isoleucine measures. Other amino acids are less frequently used for dating, primarily because of difficulties in isolation techniques. Applications Data from the geochronological analysis of amino acid racemization has been building for thirty-five years. Stratigraphy, oceanography, paleogeography, and paleoclimatology have been particularly affected. Their applications include dating correlation, relative dating, sedimentation rate analysis, sediment transport studies, sea level determinations, and thermal history reconstructions. Paleobiology and archaeology have also been strongly affected. Bone, shell, and sediment studies have contributed much to the paleontological record, including the hominoid. Verification of radiocarbon and other dating techniques by amino acid racemization and vice versa has occurred. The 'filling in' of large probability ranges, such as with radiocarbon reservoir effects, has sometimes been possible. Paleopathology and dietary selection, paleozoogeography and indigineity, taxonomy and taphonomy, and DNA viability studies abound. The differentiation of cooked from uncooked bone, shell, and residue is sometimes possible. Human cultural changes and their effects on local ecologies have been assessed using this technique. The expression of non-racemic amino acids is only known to occur through the life process therefore they have been searched for in meteorites and lunar samples, and will be sought on Mars, thus contributing to studies on extraterrestrial life and the origins of life. Other extreme environment studies concern racemization repair mechanisms in extreme cold dormant states and hydrothermal vent populations. The slight reduction in this repair capability during aging is important to studies of longevity and old age tissue breakdown disorders, and allows the determination of age of living animals. Amino acid racemization also has a role in tissue and protein degradation studies, particularly useful to developing museum preservation methods. These have produced models of protein adhesive and other biopolymer deteriorations and the concurrent pore system development. Forensic science can use this technique to estimate the age of a cadaver or an objet d'art to determine authenticity. Food adulteration and harsh processing affect its normal racemization ratio, as can bacterial contamination. This can also affect its nutritional value, taste, and aroma. Likewise, many drugs require D or L specificity for effective activity. Non-biological applications This specificity, or chirality, also has numerous nonbiological applications such as in solvent adsorption characteristics and nanomaterial development. Its' widespread applications have led to widespread dispersal of the equipment necessary for chiral determinations, and to development of multiple techniques. Procedure Amino acid racemization analysis consists of sample preparation, isolation of the amino acid wanted, and measure of its D:L ratio. Sample preparation entails the identification, raw extraction, and separation of proteins into their constituent amino acids, typically by grinding followed by acid hydrolysis. The amino acid hydrolysate can be combined with a chiral specific fluorescent, separated by chromatography or electrophoresis, and the particular amino acid D:L ratio determined by fluorescence. Or, the particular amino acid can be separated by chromatography or electrophoresis, combined with a metal cation, and the D:L ratio determined by mass spectrometry. Chromatographic and electrophoretic separation of proteins and amino acids is dependent upon molecular size, which generally corresponds to molecular weight, and to a lesser extent upon shape and charge. External links Fundamentals of sample age determination from its amino acid racemization by Policarp Hortolà Jeffrey L. Bada Amino Acid Geochronology Laboratory Amino Acid Dating The Amino Acid Geochronology Lab Racemization by Kozue Takahashi New Optical Probes of Chiral Molecules Reference List from University of Delaware Research Group PaleoDNA University of York BIOARCH v d e Chronology Major subjects Time · Astronomy · Geology · Paleontology · Archaeology · History Portal:Time Time Portal Eras and Epochs Calendar Eras: Ab urbe condita · Anno Domini / Common Era · Anno Mundi · Spanish era · Before Present · Hijri Egyptian · Sothic cycle · Hindu units of measurement · Hindu Yugas Regnal year: Canon of Kings · King lists · Limmu · Seleucid era · Era name: Chinese · Japanese · Korean Calendars Pre-Julian Roman · Original Julian · Proleptic Julian · Revised Julian Gregorian · Proleptic Gregorian · Old Style and New Style Lunisolar · Solar · Lunar · Islamic · Chinese sexagenary cycle Astronomical year numbering · ISO week date Astronomic time and techniques Astronomical chronology · Cosmic Calendar · Ephemeris · Galactic year · Metonic cycle · Milankovitch cycles Geologic time scale and techniques Deep time · Geological history · Geological time units: Eons · Eras · Periods Epoch Age Dating Standards: GSSA GSSP Chronostratigraphy · Geochronology · Isotope geochemistry · Law of superposition · Optical dating · Samarium-neodymium dating Archaeological techniques Dating methodology Absolute dating · Incremental dating · Archaeomagnetic dating · Dendrochronology · Glottochronology · Ice core · Lichenometry · Paleomagnetism · Radiocarbon dating · Radiometric dating · Tephrochronology · Thermoluminescence dating · Uranium-lead dating Relative dating · Seriation · Stratification Genetic techniques Amino acid dating · Molecular clock Related topics Chronicle · New Chronology · Periodization · Synchronoptic view · Timeline · Year zero · Circa · Floruit Retrieved from http://en..org/wiki/Amino_acid_dating Categories: Dating methodsHidden categories: March 2007 | All articles lacking sources | articles needing context | Cleanup from March 2007 | All pages needing cleanup Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Italiano This page was last modified on 17 June 2008, at 20:44
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