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
•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