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NATS 1760- GENOMES.docx

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Natural Science
NATS 1760
Darrin Durant

NATS 1760 DARRIN DURANT/ JAMES ELWICK Monday, February 25, 2013 EXCERPT FROM GENOMES & WHAT TO MAKE OF THEM (pg. 335-341) Barry Barnes & John Dupre  Genes are material objects defined and identified in terms of function - Its chemical structure had to give it the capacity to function as genes functioned 1) Complex and capable to a very high degree of variation; one of its functions is to transmit extraordinary range of variations into visible patterns and form manifest in the macroscopic realm of living things 2) Stable; if that variation were to be transmitted with the accuracy and reliability, and to a degree of instability required to account for mutation 3) Rapidly and accurately replicated; copies of genes of even a single individual organism passed into countless billions of sperm cells, each capable of transmitting full range of organism’s phenotypical traits  Scientists identified genetic material in chromosomes, but then realized that DNA possessed same attributes  Stereochemical structure of DNA by Watson & Crick in 1953 - Helical model of DNA showed how the molecule can incorporate systematic variations but it also suggested a possible mode of replication of the molecule that preserves that variation intact - Derived from four components 1) Adenine 2) Cytosine 3) Guanine 4) Thymine  Watson- Crick model identified the organic bases as strung out along a stable linear chain in ordered sequence, with two such chains linked together in parallel through a weak form of chemical bonding (double helix model) - Thymine (T) always to Adenine (A), and cytosine (C) always to guanine (G)  Two key functions of DNA 1) it must replicate and in this process letters of the text are ‘read’ single rather as instructions are read  A calling for T, and C calling for G; so that it can be imagined as the ‘instructions’ for the manufacture of its complement 2) DNA made a difference to the macro-construction of organisms largely through having a role in the synthesis of different proteins  text of the DNA is ‘read’ as words of three letters; the protein consisted of amino acids and lexicon constructed ‘genetic code’ where codon stands for a given amino acid  first DNA is ‘transcribed’ into shorter strands of DNA and then Uracil (U) replaced Thymine (T) in the four letter text it carries  RNA ‘text message’ is then ‘translated’ into the protein itself  The human genome defined as the entirety of the DNA in a human call would contain all the sequences relevant for producing a human  The Drosophila genome would have all those relevant in producing a fruit fly  The history of science may then best be though of as primarily a history of changing methods and practices oriented to the study of specifically scientific objects or epistemic objects (Hans-Jörg Rheinberger) 
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