LS3-3-10 - Lecture 3 Weak (& strong) Interactions between...

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Lecture 3 Interactions between atoms DNA Structure DNA helical stability Allison: p 22-28
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Chemical bonds Two atoms interact by sharing electrons -- holds atoms within a molecule together ( intra-molecular bonding) -- Single bond: two atoms sharing 1 pair of electrons, free rotate -- Double bonds: two atoms sharing 2 pairs of electrons, can not rotate -- Bond strength is ~110 kcal/mol = the energy needed to break the bond STRONG - Covalent bonds
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Polar and non-polar molecules -the structure of a water molecule Polar molecules Water H 2 O Nonpolar molecules Oxygen O 2 Methane CH 4
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- Attractive force between positively and negatively charged atoms - In ionic bonds, atoms gain or lose electrons completely to its partner - Strongest noncovalent bond (7 kcal/mol) Four WEAK (noncovalent) Interactions Ionic, Hydrogen bonds, Hydrophobic interactions, And Van der Waals Forces (1-7 kcal/mol) (1) Ionic Interactions
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- H bond is the electrical attraction between a hydrogen atom of one molecule and highly electronegative atom in another molecule. -form when a hydrogen atom is “sandwiched” between two electron- attracting atoms such as O and N. e.g. O-H O O-H N N-H O N-H N Hydrogen bond (2) Hydrogen bonds 3.4Å 2.7Å 3.1Å Involves polar molecules ~3 kcal/mol
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high-order structures of polymers, e.g.
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This note was uploaded on 04/26/2010 for the course LS 252-009-20 taught by Professor Chen during the Spring '09 term at UCLA.

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LS3-3-10 - Lecture 3 Weak (& strong) Interactions between...

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