Test: Replication (NCERT) - NEET MCQ

Mathew Meselson and Franklin Stahl (1958) conducted various experiments using isotopically labelled DNA of Escherichia coli to provide evidence in favour of semije mode of DNA replication. various experiments Escherichia coli to on conservative mode notes the renlisation of DNA replication.

In eukaryotes, the replication of DNA takes place at S-phase of the cell cycle. The replication of DNA and cell division cycle should be coordinated. A failure in cell division after DNA replication results into chromosomal anomaly.

Synthesis of DNA by DNA polymerases occurs only in 5'→3' direction. One strand called leading strand , is copied in the same direction as the unwinding helix. The other strand is known as lagging strand. Replication of lagging strand is in a dicontinuous way , and in the direction of growth of lagging stand is 3'→5' though in short segments of DNA which are always in the 5'→3' direction. These short segments are called Okazaki fragments joined together by the action od DNA ligase.

DNA polymerases are incapable of initiating replication by themselves. Furthermore, replication does not begin at arbitrary locations on the DNA. In E. coli, replication starts at a specific site on the DNA, known as the origin of replication.
Replication initiates at a definite region in E. coli DNA known as the origin of replication.

DNA ligase is the enzyme that joins the discontinuously synthesized fragments (Okazaki fragments) on the lagging strand.