Question

Write an essay on DNA replication.

Answer 1

• DNA replication is the process of copying a double-stranded DNA molecule. This process is observed in both eukaryotes and prokaryotes. It occurs in the nucleus in the eukaryotes and in the cytoplasm in the prokaryotes.
• There is only one active replication site in prokaryotes whereas eukaryotes have many replication sites. The process is a semi-conservative method. During the initiation of DNA replication, the DNA unwinds with the help of the helicase enzyme and becomes single-stranded.
• The structure thus formed is called a replication fork. The single-stranded DNA strand acts as a template strand. With the help of a polymerase enzyme, the new DNA strand starts synthesizing from an RNA primer. This new DNA strand is complementary to the template strand.
• In this, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). Since DNA is anti-parallel, the two strands are formed, which is the leading strand and lagging strand.
• The elongation takes place in 5' to 3' direction as polymerase can only add the nucleotides in a 5'-3' direction. Hence, the leading strand is synthesized continuously. The lagging strand is in a 3'-5' direction and must require Okazaki fragments to attach to the corresponding code and be joined by DNA ligase so that the lagging strand becomes continuous.
• The termination takes place when DNA polymerase reaches the end of the strand.