IB›IB Biology HL›Mind mapsA1.2 Nucleic acidsIB Biology HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsNucleotidesPhosphate + pentose sugar + nitrogenous baseJoined by condensationStrong covalent sugar–phosphate backboneDNA is the genetic material of living organismsDNA vs RNADNA: two strands; RNA: oneDNA has thymine; RNA has uracilDNA has deoxyribose; RNA has riboseDeoxyribose lacks the O at carbon 2Base pairs: A–T and G–CDouble helixStrands are antiparallelHeld by hydrogen bonds between basesPurines (A, G) have two ringsPyrimidines (C, T, U) have one ringPurine–pyrimidine pairs give constant widthConserved code shows common ancestryNucleic acidsDNA and RNAATGCUDirection, packingPhosphate links 5' carbon to 3' carbonNucleotides are added only to the 3' endReplication and transcription run 5'→3'Nucleosome: DNA wrapped round eight histonesExtra histone on the linker DNAKey experimentsHershey–Chase: ³²P (DNA) entered bacteria, ³⁵S stayed outResult: DNA is the genetic materialChargaff: A ≈ T and G ≈ CChargaff falsified the tetranucleotide hypothesisOne contradicting result can reject a hypothesisExam tipsMemory aid: Pure As Gold = purines A, GChargaff falsified, not proved, a hypothesis