Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction
Property 2 - it must replicate accurately so progeny cells have the same genetic makeup
Property 3 - it must be capable of some variation (mutation) to permit evolution
1928 - Griffith discovered a “transforming principle” in heat killed bacteria (Property 1)
1944 - Avery demonstrated that the transforming principle is sensitive to DNase
1952 - Hershey & Chase used 32P and 35S labelling, of bacteriophage T2 DNA and protein respectively, to show only the DNA enters the host cell and can be passed to progeny phage (consistent with Property 2)
Speed of DNA replication: 3,000 nucleotides/min in human 30,000 nucleotides/min in E.coli
Accuracy of DNA replication: Very precise (1 error/1,000,000,000 nt)
Taylor and co-workers (1957)
after one further replication
in unlabelled media
Bi-directional replication in E. coli
Only One Replication Origin in E. coli
Eukaryotes replicate their DNA only in S-phase
Eukaryotes have larger chromosomes
Replication speed 2,600 npm.
Largest Drosophila chromosome is 6.5 x 107 nucl., but it can replicate in 3-4 min. From a single origin, bidirectional replication would take 8.5 days. ==> The chromosome must have some 7,000 origins of replication.
Origins initiate replication at different times.
Two DNA polymerases are involved in eukaryotic replication
DNA polymerase d has no primase activity and is thought to be the polymerase that synthesizes the leading strand.