DNA Structure and Replication
DNA carries the genetic instructions for all living organisms. Scientists like Watson, Crick, and Franklin discovered its famous double helix structure, while Chargaff established the base pair rule (30:30:20:20) showing that DNA's bases pair in predictable ways.
The DNA molecule has a "backbone" made of deoxyribose sugar and phosphate groups, with "rungs" formed by nitrogenous bases. Each DNA strand runs in opposite directions (antiparallel), with one strand running 5' to 3' and the other 3' to 5'. A complete nucleotide consists of a nitrogenous base, deoxyribose, and a phosphate group.
DNA replication begins when an enzyme called helicase unzips the DNA strands. Single-stranded binding proteins hold the DNA open while RNA primase and primers mark where replication should begin. DNA polymerase then builds new complementary strands. The leading strand is built continuously, while the lagging strand is created in fragments called Okazaki fragments, which are later joined by ligase.
Remember this! The Hershey-Chase experiment proved that genetic information is stored in DNA, not proteins - a revolutionary discovery that changed our understanding of genetics forever.
