Describe the process of dna replication

(i) Origin of replication: It is the start point where DNA replication begins at a specific point where intertwined DNA segments start unwinding. In prokaryotic cells, there is a single origin of replication, whereas in eukaryotic cells, there are numerous origins which merge during replication. (ii) Unwinding of two DNA strands: It takes place in the presence of helicases which unwind the helix and topoisomerases which break and reseal one strand of DNA. Unwinding of DNA leads to the formation of a Y-shaped structure of the two strands of the DNA duplex. This is known as the replication fork. (iii) Synthesis of primer: It is a stretch of RNA formed on the DNA where synthesis of new DNA starts. The DNA-directed RNA polymerase synthesises the primer strands of RNA for leading and lagging strands. New strands grow from the fork, and as replication proceeds, it appears as if the point of divergence at the fork is moving. (iv) Synthesis of leading (continuous) strand: The synthesis of the continuous strand (new) of DNA is formed in the 5′–3′ direction on the 3′–5′ DNA template because of the addition of deoxyribonucleotides at the 3′ end of primer RNA. This process occurs in the presence of DNA polymerase and ATP. One new strand is formed in a continuous stretch in the 5′–3′ direction and is called the leading strand. (v) Formation of lagging (discontinuous) stand: In the second parental strand, the enzyme primase forms the RNA primer. The enzyme DNA polymerase synthesises the DNA in the form of short stretches once again in the 5′–3′ direction starting from a RNA primer. These short DNA segments, consisting of numerous nucleotides, are called Okazaki fragments. The Okazaki short segments are joined by the enzyme DNS ligase. This newly synthesised second DNA strand is called the lagging strand because it is formed later on in reference to the first continuous strand.