DNA Replication PDF

L1: DNA Replication L1: DNA Replication  L1: DNA Replication DNA Replication is the process by which DNA makes a copy of itself during cell division.  L1: DNA Replication What is need of replication? When DNA replicates during cell cycle?  L1: DNA Replication What...

L1: DNA Replication L1: DNA Replication  L1: DNA Replication DNA Replication is the process by which DNA makes a copy of itself during cell division.  L1: DNA Replication What is need of replication? When DNA replicates during cell cycle?  L1: DNA Replication What are similarities in replication of prokaryotes and eukaryotes?  Origin of replication usually contains AT rich sequences.  Replication is bidirectional from replication origin.  Replication is semi-conservative process  Replication occurs in 5’3 direction and is template dependent process  Replication is semi-discontinuous process.  DNA polymerase cannot initiate replication, its needs free 3’OH group for extension of strand  L1: DNA Replication What are differences in replication of prokaryotes and eukaryotes?  In prokaryotes DNA is always accessible to replication machinery but in eukaryotes it not directly accessible, it is bound to nucleosome.  In prokaryotes, often there is single origin from where replication starts while eukaryotes, has multiple origin from replication can be initiated.  Prokaryotic chromosomal DNA replication stops at one specific locus while in case of eukaryotes at stops at all those locus where two replication fork meets.  Multiple rounds of replication are possible during prokaryotic cell division while in eukaryotes only one round of replication is possible per cell division.  For linear chromosomes, which are most common in eukaryotes, a special problem arises during replication of chromosomal ends (telomeres).  L1: DNA Replication What are possible modes of replication? L1: DNA Replication L1: DNA Replication  L1: DNA Replication How we can say that replication is also semi-conservative in eukaryotes? J. Herbert.  L1: DNA Replication J. Cairns E.coli culture grown on tritium labeled thymine Autoradiographs were made for the radiolabelled DNA. Analysis of DNA at different time points during replication  L1: DNA Replication Deoxynucleoside 5’ triphosphates (dNTPs)  L1: DNA Replication The new strand of DNA is synthesized from 5’ to 3’ New nucleotides are added one at a time to the 3’ hydroxyl end of the DNA chain, forming new phosphodiester bond. The 3’-5’ parental strand act as template.  L1: DNA Replication DNA replication is semi- discontinuous Continuous DNA synthesis occurs on leading strand DNA Replication Is discontinuous on lagging strand L1: DNA Replication  L1: DNA Replication Reiji and Tuneko Okazaki in 1969 The DNA is copied in short segments (1000–2000 nt in prokaryotes and 100–200 nt in eukaryotes) on lagging strand L1: DNA Replication L1: DNA Replication L1: DNA Replication L1: DNA Replication