CHAPTER 8 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; mutagenesisLearning goals:
•Nucleic acids are polymers of nucleotides used for:–storage of genetic info (DNA)–transmission of genetic info (mRNA)–processing of genetic information (ribozymes)–protein synthesis (tRNA and rRNA)•Nucleotides are also used in the monomer form for cellular functions:–energy for metabolism (ATP)–enzyme cofactors (NAD+)–signal transduction (cAMP)Functions ofNucleotides and Nucleic Acids
Nucleotides and Nucleosides•Nucleotide = –nitrogeneous base–pentose–phosphate•Nucleoside = –nitrogeneous base–pentose•Carbon AND nitrogen atoms on the nitrogenous base are numbered in cyclic format. •Carbons of the pentose are designated N’ to alleviate confusion.
Phosphate Group•Negatively charged at neutral pH •Typically attached to 5’ position–Nucleic acids are built using the 5’-triphosphates version of the nucleotide.•ATP, GTP, TTP, CTP–Two of the three phosphates used for building nucleic acids form a leaving group, and completed nucleic acids contain one phosphate moiety per nucleotide.•May be attached to other positions for specialized function
Other Nucleotides:Monophosphate Group in Different Positions
Pentose Forms Differ in Some Nucleic acids and Nucleotides-d-ribofuranose in RNA-2’-deoxy-d-ribofuranose in DNA•Different puckered conformations of the sugar ring are possible.
Nitrogenous Bases•Derivatives of pyrimidine or purine•Nitrogen-containing heteroaromatic molecules•Planar or almost planar structures•Absorb UV light around 250–270 nm
Pyrimidine Bases•Cytosine, adenine, and guanine are 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.•Neutral molecules at pH 7
NomenclatureTABLE 8-1Nucleotide and Nucleic Acid NomenclatureBaseNucleosideNucleotideNucleic acidPurinesAdenineAdenosineDeoxyadenosineAdenylateDeoxyadenylateRNADNAGuanineGuanosineDeoxyguanosineGuanylateDeoxyguanylateRNADNAPyrimidinesCytosineCytidineDeoxycytidineCytidylateDeoxycytidylateRNADNAThymineThymidine or deoxythymidineThymidylate or deoxythymidylateDNAUracilUridineUridylateRNANote: “Nucleoside” and “nucleotide” are generic terms that include both ribo- and deoxyribo- forms. Also, ribonucleosides and ribonucleotides are here designated simply as nucleosides and nucleotides (e.g., riboadenosine as adenosine), and deoxyribonucleosides and deoxyribonucleotides as deoxynucleosides and deoxynucleotides (e.g., deoxyriboadenosine as deoxyadenosine). Both forms of naming are acceptable, but the shortened names are more commonly used. Thymine is an exception; “ribothymidine” is used to describe its unusual occurrence in RNA.