Spring 09 lecture 03

Spring 09 lecture 03 - Nucleic Acid Structure and...

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Nucleic Acid Structure and Hybridization DNA and RNA structure Learning Objectives: Explain the chemical forces determining DNA structure. Describe how base pairs can be identified in the major groove based on H-bond donors and acceptors.
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Chemical bonds: Covalent: -strong - atoms within individual molecule are held together in the molecule by sharing electrons in their outer atomic orbital -covalent bonds can be nonpolar or polar (depends on electro-negativity) -in a polar covalent bond atoms involved get partial charges (+ or -), feature that lets them to make hydrogen bond -do not change in water (why is this important) Ionic Noncovalent: -within individual molecule and between oppositely charged ions (huge difference in electro-negativity) -complete transfer of electrons. -weak in water
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Noncovalent: - polarity: H atom covalently attached to a very electronegative atom (N, O or P; donors, D ) has partial positive charge -partially positive H could be attracted by another electronegative atom (acceptor, A ) and it can form a weak hydrogen bond with it. -Weak in water Hydrogen bonds
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Van der Waals interactions Noncovalent: -Between all types of molecules (nonpolar AND polar) -cause is transient, unequal movement and distribution of electrons – formation of temporary dipoles; -dipole of one molecule “helps” electrons of the second molecule to arrange into dipole (+ve attracts –ve)… -those interactions decrease with distance, but if too close - repulsion -works well only if few atoms from one molecule are at the same distance from
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This note was uploaded on 08/03/2009 for the course BIOL BIOL308 taught by Professor Miskovic during the Spring '09 term at Waterloo.

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Spring 09 lecture 03 - Nucleic Acid Structure and...

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