This course focuses on the principles of nucleic acid structure. The scope of this course is to go beyond the common DNA structures such as B-DNA and A-DNA helical structures. The course will concentrate on other DNA structural motifs like branched DNA, supercoiled DNA, triplex DNA, and quadruplex DNA. Physical characterization of these structures as well as the functional implication of these structures (in terms of DNA replication, transcription, telomeres, etc.) will be discussed extensively. Discussion will also center on the forces that stabilize these structures, such as H-bonding and stacking interactions. The course will also cover other important DNA structural motifs such as curved or bent DNA as found in A-tracts and the relevance of these structures in promoter recognition and gene expression. Important RNA structures, such as ribozymes and pseudoknots, will be discussed. We will also discuss the significance of DNA structural motifs in eukaryotic genomes and the application of bioinformatic tools to search for these motifs.