Question

What triggers DNA replication?

Answer 1

DNA Replication:

1. The process by which the double-stranded DNA molecule replicates to form multiple copies.
2. The replication of DNA is semiconservative (the new strands are synthesized from the old strand).
3. The process of DNA replication has three steps: Initiation, Elongation, and Termination.

Initiation:

1. The first step of DNA replication is the unwinding of Double-stranded DNA at the site called the origin of replication (ORI) by the enzyme helicase.
2. Helicase unwinds DNA from a small section of DNA called the origin of replication (from where replication of DNA starts).
3. A replication bubble is an unwound open region of the DNA helix from where the replication of DNA occurs.
4. The replication bubble is assumed like a zipper that is unzipped in the middle forming a little open pucker.
5. For initiation of DNA replication on two strands a short segment of RNA primer is required.
6. RNA primer contains 10-12 nucleotides complementary to DNA template strands.
7. The DNA polymerase lll enzyme begins to add deoxynucleotides to the template strand and initiates to synthesize a new strand.

Elongation:

1. The DNA polymerase enzyme keeps on adding the complementary deoxyribonucleotides to the template strand and elongates the new strand.
2. The synthesis of new strands in two antiparallel strands (template) of DNA occurs in a continuous and discontinuous way, forming a replication fork.
3. The template strand having polarity 5'-3' in which continuous synthesis of DNA takes place without the formation of Okazaki fragments, thus called the leading strand, but the other template strand having polarity 3'-5' in which discontinuous synthesis of DNA takes place with the formation of Okazaki fragments, thus called lagging strand.

Termination:

The replication of DNA in prokaryotes is terminated when two replication forks meet at a point, while in eukaryotes the replication of DNA is terminated by telomers in telomerase.