Question

1. Describe DNA synthesis (replication) in your own words clearly enough that someone could visualize what is happening.

Answer 1

DNA replication is the process of producing two identical copies of the parent DNA molecule from the parent DNA template. It occurs in vivo in all living organisms. DNA replication is the basis of the biological inheritance.

DNA replication occurs with the help of the replication enzyme DNA polymerase which adds nucleotides at the 3' end of the growing chain. The main steps of DNA replication include -

1. Initiation
2. Elongation
3. Termination

The picture depicted below shows the DNA replication machinery

The main important events in DNA replication includes-

1. Helicase unwinds the double-stranded DNA into single-stranded
2. The single-stranded binding proteins bind to the unwound single-stranded DNA stabilizing it and preventing the double helix formation
3. Primase adds primers and the DNA polymerase adds nucleotides and leading strand is synthesized continuously in 5' to 3' direction
4. The lagging strand is synthesized discontinuously as short fragments called Okazaki fragments
5. DNA ligase then joins the Okazaki fragments
6. Termination occurs when the polymerase reaches the termination site

DNA replication occurs in vitro by a process called polymerase chain reaction (PCR) in a thermal cycler in the presence of Polymerase enzyme, DNA template, primer, dNTPs, Buffer and MgCl2.