In this episode of BioSpeak, we examine the molecular structure of DNA’s double helix, focusing on nucleotides as the essential building blocks of DNA. We cover how DNA’s backbone is created through phosphodiester bonds between deoxyribose sugars and phosphate groups, with each sugar bonded to a nitrogenous base: Adenine, Cytosine, Guanine, or Thymine. By looking at complementary base pairing, we explain why DNA strands run in opposite directions (5’ to 3’). Lastly, we discuss how DNA compacts into chromosomes by winding around histones to store extensive genetic information and share the remarkable fact that all humans share 99% of their DNA.