Class09

Class09 - Chemical Evolution From volcanic gases to micro...

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Unformatted text preview: Chemical Evolution From volcanic gases to micro- molecules (the precursors for biological molecules) What is chemical evolution? • Chemical evolution is the natural conversion of smaller molecules to large biological molecules • Chemical evolution was first suggested by a Russian biochemist, Aleksandr Oparin • Oparin’s Hypothesis (1924): biological evolution was preceded by chemical evolution, i.e., the first biological molecules were produced from non- living matter [volcanic gases of the second atmosphere] before life began • Then biomolecules somehow came together to produce living matter Formation of Earth Oldest recorded fossils 4.5-4.8 B 3.3 B 1.2-1.5 B Evolution of biological chemicals When did chemical evolution occur? Years Ago What are the chemical characteristics of biological molecules? • Composition : biomolecules frequently involve the more abundant elements of C, H, N, O, P, and S • Size : biomolecules are frequently large (MW > 10000 u) and have large carbon frameworks – C uniquely forms strong bonds with all the above elements including itself – C always requires 4 bonds to get to inert gas structure and the bonds may be single, double, or triple – Structure of C compounds may be chains or rings C n H 2n+2 n = 60-100 C n H 2n C n H 2n-2 C n H 2n C 6 H 6 Hydrocarbons are compounds containing only C and H How can large be represented by simplified structural formulas? • Large molecules make it necessary to replace Lewis structures with simpler representations – Condensed structural formulas : represent individual C-H bonds collectively with subscripts – Bond line formulas : bonds are represented as lines, C atoms, H atoms and C-H bonds are omitted, but bonds to other atoms as well as all other atoms are shown I s o m e r s o f C 5 H 1 2 Condensed Formula Bond Line formula http://butane.chem.uiuc.edu/cyerkes/Chem204sp06/Lecture_Notes/lect14c.html Isomers are different substances with the same molecular formula Lewis Formula These replacements (called functional groups ) become the reactive sites of the molecule while the rest of the original hydrocarbon molecule is relatively unreactive. OH NH 2 Derivatives result when a H atom of a hydrocarbon is replaced by some other atom or group of atoms. H Replace H with NH 2 Replace H with OH ethane R-X Unreactive hydrocarbon residue called alkyl radical Functional Group - reactive atom or groups of atoms Derivatives of hydrocarbons that have the same functional group are called families of hydrocarbons • Since reactions of derivatives of hydrocarbons depend only on the functional group, all members of a family of hydrocarbons have the same reactions • The general formula for a family of derivatives of hydrocarbons is RX http://www.doctortee.com/dsu/tiftickjian/cse-img/biology/chemistry/functional-groups.jpg Functional Groups Frequently Found in Biological Molecules How can energies needed to introduce functional groups into hydrocarbons be estimated?...
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Class09 - Chemical Evolution From volcanic gases to micro...

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