Lecture 9 Bio325 Fall 07

Lecture 9 Bio325 Fall 07 - The relationship between...

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1 The relationship between chromosomes, genes, and deoxyribonucleic acid (DNA): critical experiment by Griffith (1928): Fig. 6.3 continuation and simplification of transformation experiment by Avery (1931): Fig. 6.4
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2 Deoxyribonucleic acid ( DNA ): • Each strand of DNA is a polymer composed of repeating units of nucleotides • A nucleotide consists of a base, a deoxyribose sugar, and a phosphate • each DNA strand has directionality; the direction is determined by the orientation of the sugar in relation to the phosphate backbone. The sugar is connected to the adjacent phosphates at the 3rd and the 5th carbon atoms of the pentose ring. Thus, every DNA strand has a 5’ end and a 3’ end. P P 1 2 3 4 5 base phosphate Deoxyribonucleic acid ( DNA ): a polymer of nucleotides The Watson/Crick model of DNA structure (1953): • strands are antiparallel • bases are inside, phosphates outside • ~10 bp per turn • right-handed double- stranded helix Fig. 6.9
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3 • There are 4 types of bases in DNA: adenine (A),thymine (T), guanine (G), and cytosine (C) • A and G are purines , T and C are pyrimidines • The bases are held together in double- stranded DNA by hydrogen bonds •A pairs with T; G pairs with C; therefore [A]=[T] and [G]=[C] • there are 2 hydrogen bonds in a A-T basepair, and 3 hydrogen bonds in a G-C base pair. For this reason, G-C base pairs are kinetically more stable than A-T base pairs The bases in DNA: • the helix is held together by the stacking
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This note was uploaded on 06/19/2008 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas at Austin.

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Lecture 9 Bio325 Fall 07 - The relationship between...

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