BIOC 2580 Study Guide - Furanose, Nucleoside, Heterocyclic Compound

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30 Nov 2011
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BIOC 2580 Final Exam Notes
3. Nucleic Acids
Structure
Linear polymers of nucleotides connected via phosphodiester bonds
Nucleotide: repeating unit consisting of sugar, base and phosphate group
2 types of nucleic acid sugars: ribose, deoxyribose
4 different bases: cytosine, thymine (uracil), adenine, guanine
Backbone is sugar linked together by phosphates
Called sugar phosphate backbone
Bases are linked to sugars
The Bases
Numbering
Pyrimidine Bases
Single ring bases
Cytosine, thymine (5-methyluracil) and uracil (RNA)
Tautomers
Tautomers: isomers which differ only in positions of protons (and double bonds)
Skeleton remains unchanged
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Nucleotide bases can exists in 2 or more tautomeric forms depending on pH
Tautomeric Forms of Cytosine
OH group undergoes keto/enol tautomerism
NH2 group undergoes amino/imino tautomerism
amino + keto form predominates (middle)
Purine Bases
2 ring bases
Fused bicycle heterocycle
4 N atoms, 5 C atoms
Adenine and guanine
Sugars
RNA contains D-ribose
DNA contains D-2-deoxyribose
OH on C-2 is replaced with an H
Both sugars are in β – furanose (5 membered) form
Nucleosides
Nucleoside = Base + sugar
Base joined to sugar through glycosidic bond
Sometimes called glycosylic bond (C-N linkage)
Special kind of glycoside found in nucleic acids
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