Presented By DR. DINESH D. KHEDKAR Deptt. of Botany Shri Shivaji Science College Amravati

 The in vitro study of DNA replication was pioneered by Arthur Kornberg ( Nobel Prize in 1959)  Watson and Crick hinted that the replication of double helix could takes place to form a new DNA  Replication is the production of copies of the DNA (Genetic Material) during cell division  Modes of Replication 1. Conservative 2. Semi conservative 3. Dispersive

Parent Strands New Strand As parent New Strand Completely New Conservative Replication

Parent Strands New Strand One Old One New New Strand One Old One New Semi Conservative Replication

Parent Strands New Strand Mixed Old & New Dispersive Replication New Strand Mixed Old & New

Parent Strands New Strand One Old One New New Strand One Old One New Semi Conservative Replication

*In Eukaryotes,  DNA molecules are larger than prokaryotes and are not circular  Usually multiple sites of initiation of replication  Chromosome composed of many replicon *In Prokaryotes, single circular chromosome Only one replicon

Eukaryotic linear chromosome Prokaryotic Circular chromosome

Leading strand Lagging strand Fork movement

 Like virtually all metabolic processes, replication is under the control of enzymes  Three major enzymes-  DNA polymerase I (Arthur Kornberg; Nobel)  DNA polymerase II  DNA polymerase III

 Auto radiographic evidences leads us to believe that replication occurs simultaneously on both the strands  Continuous Replication (Leading)  Discontinuous Replication (Lagging)

Primer Formation Elongation Proofreading Primer Removal Ligation

The origin of replication in E. coli is termed oriC –origin of Chromosomal replication Important DNA sequences in oriC –AT-rich region –DnaA boxes

DNA sequences at the Bacterial origin of Replication

Initiation of Replication at oriC DNA replication is initiated by the binding of DnaA proteins to the DnaA box sequences –causes the region to wrap around the DnaA proteins and separates the AT-rich region

Figure 11.6 continued Uses energy from ATP to unwind the duplex DNA SSB

 Animation for DNA structure Animation for DNA structure  Animation for DNA Replication Animation for DNA Replication  Animation Test for DNA Ploymerization Animation Test for DNA

Direction of synthesis on lagging strand Direction of synthesis on leading strand 3’ 5’ 3’ 5’ 3’ 5’

Direction of fork movement Direction of synthesis Of lagging strand Direction of synthesis of leading strand