07BIS1012013ReplicLect_7

Lrodriguez 2013

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Unformatted text preview: 2’ position if OH, then Adenosine Monophosphate OH H OH H Deoxyadenosine Diphosphate Deoxyadenosine Triphosphate 2’ position - if OH, then Adenosine Diphosphate 2’ position - if OH, then Adenosine Triphosphate BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 13 5’ P O DNA is a plectonemic coil DNA plectonemic consisting of two polyconsisting nucleotide chains of DNA. nucleotide Because the 1' carbon of the O sugar bonded to the nitrogenous base limits the O rotation of the base, the -O P O H H O strands of DNA must be N CH H arranged in an antiparallel N antiparallel N O N fashion. fashion. N O HCH N N DNA is also a polyanion with DNA A T a negative charge on every phosphodiester bond. phosphodiester O H O Electrostatic repulsion H -O P O N N N causes DNA to writhe or twist writhe twist H O N violently in solution. Without N N N H stabilizing forces, N HCH O H phosphodiester bonds will C G break and the DNA will degrade. 3’ O BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez -O P O 3 O - O H C O O P - O H C 3’ O DNA Structure (p. 231) 5’ 14 H O H What are the factors contributing to DNA stability? ­Ionic bonds ­Hydrophobic interactions ­Van der Waals interaction ­Hydrogen bonds BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 15 Factors contributing to DNA stability ­ 1. Ionic bonds involve an attraction between unlike charges (e.g., 1. Ionic between the (-) carboxyl group of aspartic acid and the (+) amino group of lysine). The ability of cations like Na+ to neutralize the effects of lysine). electrostatic repulsion is a good example of the stabilizing effects of electrostatic ionic bonds. Na+ acts as a counter ion that neutralize the (-) charge on ionic counter the phosphodiester bonds. Writhing subsides and the backbone of the Writhing helix becomes more rigid or stiff. This promotes the stacking of the stacking bases, one over the other. All of this leads to greater stability of the helix. This phenomenon underscores the reasons sodium is typically added to DNA solutions in the laboratory. DNA + Na Cl + H2O = Cl- Na+ O- BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 16 DNA stability: Ionic bonds ­ ­ The ability of cations like Na+ to neutralize the effects of electrostatic repulsion is a good example of the stabilizing effects of ionic bonds. Na + repulsion acts as a counter ion that binds to the (-) charge on the phosphate counter group. Writhing subsides and the backbone of th...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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