DNA Structure

Abstract

RNAs are found only in two related conformations A and A´, which both belong to the A-family double-helical structures (Chapter 10). In contrast, DNAs can adopt several other conformations depending on environmental conditions such as counterion and relative humidity and, in synthetic polynucleotides with defined, repetitive oligonucleotide building blocks, on sequence and on composition (Chapter 9). DNA double helices are classified either as A type with A-DNA the only representative or as B type encompassing B-, B´-, C-, C´-, C″-, D-, E-, and T-DNA. Besides these right-handed double helices, a left-handed variety (Z-DNA) has been discovered (Chapter 12), adding considerably to the chameleon-like, adaptable character of DNAs.