13.DNARNA_Structure

13.DNARNA_Structure - 13. Introduction to DNA and RNA...

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13. Introduction to DNA and RNA structure Please view the “The DNA Story” on the streaming AV media reserves. 1. Go to http://lib.washington.edu/types/courses 2. Search for and select “BIOC 441” 3. Click on “Online course reserves for BIOC 441; UW NetID required” 4. Select +Streaming Media Course Reserves 5. You will be prompted for a password. Use 7popp076 6. Click on “Click here for more information” 7. Watch the video.
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§ 2’-deoxyribose sugars § Phosphodiester linkages § Directional chain (5’ to 3’) § 4 Bases Chargaf’s rule: [A] = [T], [G] = [C] DNA is a polymer of 2’-deoxyribonucleotides GCTAp 5’ end 3’ end C G T A HO-CH2 O H2N-C C C HN N N CH C O N O O O P O CH2 O O C N N CH C CH NH2 NH2 C C N N N CH C N HC O O O P O CH2 O O-PO 3 2 O O O P O CH2 O N C C O HN CH C O CH3 1’ 2’ 3’ 4’ 5’ 3’
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RNA is a polymer of ribonucleotides § ribose sugars § Phosphodiester linkages § Directional chain (5’ to 3’) § 4 Bases GCUAp C G U A 5’ end 3’ end 1’ 2’ 3’ 4’ 5’ 3’ OH HO-CH2 O H2N-C C C HN N N CH C O N O O O P O CH2 O O C N N CH C CH NH2 OH O O O P O CH2 O N CH C O HN CH C O OH NH2 C C N N N CH C N HC O O O P O CH2 O O-PO 3 2 OH
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RNA is easily hydrolyzed under alkaline conditions The reaction proceeds through a 2’,3’-cyclic monophosphate intermediate. Enzymatic hydrolysis of RNA by RNase proceeds through a similar intermediate. Because DNA lacks the 2’-OH group, it is stable under alkaline conditions. . . . . O P O- CH2 O O O N OH O O P O CH2 O O N OH O O P O O ... OH O N OH O O P O O ... HO CH2 O . . . . O P O- CH2 O O N O O P O O H + . . . . O P O- CH2 O O O N O H O O P OH O mixture of 2’- and 3’- monophosphate derivatives shortened RNA RNA H2O
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Why does DNA contain T rather than U? N CH C O HN CH C O C NH2 N N CH C O CH cytosine uracil H2O Cytosine deaminates non-enzymatically to form uracil. If this happens in DNA, it constitutes a mutation. Cells have a proof- reading system that recognizes the error and replaces the U by C. Deamination of cytosine is of less consequence in RNA, because RNA is not the permanent repository of genetic information.
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The phosphate groups of DNA and RNA are negatively charged A phosphodiester group has a pKa of about 1, and so will always be ionized and negatively charged under physiological conditions (pH ~7). Nucleic acids require counterions such as Mg2+, polyamines, histones or other proteins to balance this charge. 5’ 3’ HO-CH2 O N O O P O CH2 O O N O O P O CH2 O O N O O P O CH2 O O O-PO 3 2 N + M + M + M + M
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the β -furanose (cyclic) form 5’ 3’ HO-CH2 O N OH O P O CH2 O N O O OH O O P O CH2 O O N OH O O P O CH2 O O O-PO 3 2 N OH N 3’ 1’ 5’ 4’ endo C-2’ exo The ring can adopt various puckered conformations in which C-2’ and C-3’ are in either exo or endo positions relative to the base and C-5’. H-C=O
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This note was uploaded on 02/17/2012 for the course CHEM 212 taught by Professor Staff during the Fall '10 term at Rutgers.

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13.DNARNA_Structure - 13. Introduction to DNA and RNA...

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