DNA replication

DNA replication
Templated replication
• Sense and antisense strands: The sense strand of a double-stranded DNA molecule has a base sequence similar to that of the RNA that is transcribed from the DNA. The antisense strand (also known as template strand) has a sequence that is the reverse complement of the sense strand (base paired to it with an antiparallel 5 to 3 polarity).
• Semiconservative replication: Discovery of the double helical structure of DNA immediately suggested a mechanism for precise replication -- namely separation of the two strands and template synthesis of a new copy of each of the missing complementary strands. This model predicted that each new double helix should have one strand of parental DNA and one strand of newly synthesized DNA.
• Messelson-Stahl experiment: Semiconservative replication was demonstrated by starting with bacteria whose DNA was labeled with heavy nitrogen (15 N) and then allowing various amounts of growth to occur in media labeled with normal nitrogen. After one round of replication, the entire DNA had an intermediate density. After two rounds, one half was light and the other half still had an intermediate density. There was no conservation of heavy DNA. However, the data suggested that each of the labeled strands from the original DNA remained intact and separated from its partner in each replication cycle.