2_N&N

Lehninger Principles of Biochemistry

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Lecture 2 Nucleotides and Nucleic Acids Biological function of nucleotides and nucleic acids Structures of common nucleotides Structure of double stranded DNA Structures of ribonucleic acids Denaturation and annealing of DNA Chemistry of nucleic acids; mutagenesis Key topics :
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Readings: pp. 271-289 8 | Nucleotides and Nucleic Acids © 2009 W. H. Freeman and Company
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Functions of Nucleotides and Nucleic Acids Nucleotide Functions: Energy for metabolism (ATP) Enzyme cofactors (NAD + ) Signal transduction (cAMP) Nucleic Acid Functions: Storage of genetic info (DNA) Transmission of genetic info (mRNA) Processing of genetic information (ribozymes) Protein synthesis (tRNA and rRNA)
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Nucleotides and Nucleosides Nucleotide = Nitrogeneous base Pentose Phosphate Nucleoside = Nitrogeneous base Pentose Nucleobase = Nitrogeneous base
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Phosphate group Negatively charged at neutral pH Typically attached to 5’ position Nucleic acids are built using 5’-triphosphates Nucleic acids contain one phosphate moiety per nucleotide May be attached to other positions:
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Pentose in Nucleotides 2200 β -D-ribofuranose in RNA 2200 β -2’-deoxy-D-ribofuranose in DNA Different puckered conformations of the sugar ring are possible
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Nucleobases Derivatives of pyrimidine or purine Nitrogen-containing heteroaromatic molecules Planar or almost planar structures Absorb UV light around 250-270 nm
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Numbering the bases
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Pyrimidine Bases Cytosine is found in both DNA and RNA Thymine is found only in DNA Uracil is found only in RNA All are good H-bond donors and acceptors • Cytosine p K a at N3 is 4.5 • Thymine p K a at N3 is 9.5 Neutral molecules at pH 7
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Purine Bases Adenine and guanine are found in in both RNA and DNA Also good H-bond donors and acceptors • Adenine p K a at N1 is 3.8 • Guanine p K a at N7 is 2.4 Neutral molecules at pH 7
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Numbering the bases
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Tautomerism of nucleobases Prototropic tautomers are structural isomers that differ in the location of protons Keto-enol tautomerism is common in ketones Lactam-lactim tautomerism occurs in some heterocycles Both tautomers exist in solution but the lactam forms are predominant at neutral pH
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UV Absorption of Nucleobases Absorption of UV light at 250-270 nm is due to
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2_N&N - Lecture 2 Nucleotides and Nucleic Acids Key...

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