During DNA elongation, DNA polymerase adds complementary DNA nucleotides to the 3' end of a newly synthesized strand using the template strand as a guide. On the lagging strand, DNA polymerase can only synthesize DNA in the 5' to 3' direction, so Okazaki fragments are formed that later need to be joined together. In contrast, the leading strand is synthesized continuously because DNA polymerase can add nucleotides to the 3' end that is open for elongation as the replication fork moves along.

1. EUKARYOTIC DNAELONGATION
( LAGGINGSTRANDAND LEADING STRAND )

2. Elongation
With the help of DNA polymerase enzyme in
presence of Mg-ion, dNTP attached to template
DNA strand to form replicate DNA. During
elongation DNA polymerase adds DNA
nucleotides to 3’ end of the newly synthesized
polynucleotide strand. The template strand
specifies which of the four DNA nucleotides ( A, T,
C or G ) is added at each position along the new
chain. Only the nucleotide complementary to the
template nucleotide at the position is added to the
new strand.

4. Lagging Strand :
This a complementary strand which is formed by joining up of the short
DNA segment called Okazaki Segment or Okazaki fragment. DNA
polymerase catalyzes the polymerization only at 5’ to 3’ direction. Thus in
case of antiparallel strand of mother DNA, a small stretch of DNA
segment exposes at one time results in formation of Okazaki fragments.
An RNA primer is required every time a new Okazaki fragment is to be
formed.
Leading Strand :
This is a complementary strand which is form continuously because DNA
polymerase polymerize only in 5’ to 3’ end direction by adding them at 3’
end of sugar molecule. Thus 3’ is open for elongation.

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