L03 -2011chemistry1

L03 -2011chemistry1 - Lecture3:Thechemistryofcells:areview...

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Lecture 3:  The chemistry of cells: a review Restricted to a subset of known elements, dominated by the chemistry of  carbon  (organic chemistry) Reactions occur in  aqueous  (watery) solutions over a narrow range of temperatures ( 0-100 C ) Lecture outline Strong and weak chemical bonds H, O, C, and N: the elements of life Polar covalent bonds ; the unique properties of water Acids, bases, and phosphates Carbon compounds Polysaccharides
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“Strong” and “weak” chemical bonds contribute to the structure  of biomolecules Covalent  bonds are strong bonds (50-110 kcal/mol) Covalent bonds are formed when atoms  share pairs of electrons -C-C- bonds ~85 kcal/mol Weak “bonds” (<5 kcal/mol) Ionic bonds (~3 kcal/mol) Hydrogen bonds (~1-4 kcal/mol) van der Waals interactions (~0.1 kcal/mol) Hydrophobic interactions   (NA) We will briefly  discuss each of these today
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Electron shells (energy levels) ECB 2-5 Covalent and ionic bonds fill outer shell - stable 
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Three elements comprise >95% of the atoms in living cells #P Atomic number #e - #N Mass % *H 1 1 0 1 ~48% *C 6 6 6 12 ~24% *N 7 7 7 14 ~1% *0 8 8 8 16 ~24% Na 11 11 12 23 <0.5 Mg 12 12 12 24 <0.5 *P 15 15 16 31 <0.5 *S 16 16 16 32 <0.5 Cl 17 17 18 35 <0.5 K 19 19 20 39 <0.5 Ca 20 20 20 40 <0.5 EC B Fig . 2-4 *- Forms  covalent  bonds Other elements (Na, Mg, Cl, K, Ca) primarily form  ionic  bonds
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Atoms joined by “covalent” bonds share electron pairs In a “double bond (~150 kcal/mol),” atoms share  two pairs of electrons O=O In a “single bond (50-110 kcal/mol),” atoms share a  pair of electrons H : H or H-H In a “triple bond (~200 kcal/mol),” atoms share  three pairs of electrons C N Distance at which attraction and repulsion are equal is bon length Sharing of e- completes outer shell (both atoms can  count shared e-) ECB 2-6 ECB 2-6 C, H, N, O, P, and S form covalent bonds in cells
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Opposites attract: ions and ionic bonds Ions have a deficit or surplus of electrons,  resulting in a net + or – charge - example NaCl  (Na + Cl - ) Loss or gain of e-  completes outer shell ECB 2-6 Na, Mg, Cl, K, Ca primarily form ionic bonds  in cells
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