MBIO 3410 lecture Sept 13 2007

MBIO 3410 lecture Sept 13 2007 - Outline-last lecture...

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1 Outline-last lecture Nucleic acid structure Bases Nucleosides Nucleotides Phosphodiester bonds Chargaff’s Rules DNA double helix DNA/RNA sequence Hydrogen bonds Chemical and physical properties of nucleic acids Stability of nucleic acids RNA secondary structure RNA vs. DNA Effect of acid (DNA/RNA) Effect of alkali (DNA) Effect of alkali (RNA) Chemical denaturation Spectroscopic and thermal properties of nucleic acids UV absorption Hypochromicity Quantitation of nucleic acids Purity of DNA Thermal denaturation Renaturation – Calculating T m
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2 What types of nucleic acids make up genomes? Dependent on the organism: Viruses can have ds DNA, ss DNA, or RNA based genomes Most eukaryotes have single linear ds DNA Prokaryotes have a circular ds DNA molecule i.e. lack free 5’ and 3’ ends Some prokaryotes have extra- chromosomal DNA molecules called plasmids (circular ss or ds DNA) Fig 1.12 polyoma virus ex circular ds DNA RuvB protein bound to ds linear DNA Copyright © 1994-2005 Lisa Iype, Cox & Inman bccm.belspo.be/newsletter/8-00/images/bccm02.jpg
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3 Closed circular DNA Two single strands are circular and linked together # of double-helical turns = linking # ( Lk ) Bacterial plasmids and chromosomes Many viral DNA
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4 Supercoiling: Is the coiling of the DNA axis upon itself Most DNA in nature is a –ve supercoil +ve supercoil = twisting of the DNA is in the same direction as the double helix, if the helix is untwisted then the supercoiling is –ve Quantification of supercoiling Change in linking # (Δ Lk ) from the relaxed closed circle ( Lk º) i.e. the # of 360º twists before ring closure DNA isolated from cells has ~6 turns/100 turns of helix (1000 bp) Δ Lk / Lk º = -0.06
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5 Fig 1.13
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MBIO 3410 lecture Sept 13 2007 - Outline-last lecture...

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