Difference Between Leading DNA Strand and Lagging DNA Strand

For continuation of life on earth living organisms go through the process of giving birth to offspring which look alike them, this characteristic of passing genes is only seen in living beings.


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Dera fuel requirements of the passing of these genes, the major requirement is DNA. DNA stands for deoxyribonucleic acid, It is mainly responsible for inheritance and transmission of characteristics of a person into their offspring.

DNA and chromosome main constituent. It is present in all living beings, animals or humans, and is considered to be an important part of the human life cycle. The process through which characteristics are passed on to the next generation of offspring is known as DNA replication.

It is the procedure through which DNA is copied. Double-stranded molecules replicate to produce two identical copies of molecules. DNA splits forming a fork. Replication of strands goes into different ways.

The replication fork forms within long helical DNA during DNA replication. This is created by helicases, which break the hydrogen bonds holding the two DNA strands together in the helix. This results in two “prongs”, each one having a single strand of DNA.

DNA is read by DNA polymerase in 3’-5’ direction or 5’-3’ direction. These are commonly classified as leading DNA strand and lagging DNA strand, both of them are completely different and opposite to each other which makes reading sometimes difficult. 

Leading DNA Strand vs Lagging DNA

The difference between the leading DNA strand and lagging DNA strand is of synthesis of DNA strands, the leading DNA strand synthesized in 5′-3′ direction, on the other hand, lagging DNA strand synthesized in 3′-5′ direction. Both of them helps in process of replicating DNA but in different ways. 

Leading dna strand vs Lagging dna strand

Comparison Table

Parameters of ComparisonLeading DNA StrandLagging DNA Strand
DefinitionSingle strands which help in replicating DNA through synthesis without any break.Double strands which help in replicating DNA through synthesis with Okazaki fragments.
Direction of synthesis5’- 3’ direction3’- 5’ direction
Direction of movementMoves in the direction of movement of the fork.Move opposite from the direction of movement of the fork.
The requirement of RNA primerDoes not require an RNA primer.Requires RNA primer
Helicase wrapped aroundEukaryotesProkaryotes 

What is Leading DNA Strand?

The leading DNA strand is the strength which synthesizes in the direction of replication fork movement or 5’-3’ direction. This strand is made continuously without any break.

After polymerase reads the original DNA template, nucleotides continuously get added to the 3rd end of the strand and this makes the leading stand. They are single DNA strands that help in the replication of DNA. Synthesis of leading DNA strands does not require an RNA primer.

The Helicase is nothing but a composition of six polypeptides that combine into one strand of the DNA that is being replicated. As helicase unwinds DNA at the replication fork, the DNA ahead is forced to rotate. This process results in a build-up of twists in the DNA ahead.    

Bare single-stranded DNA has the possibility to fold back on itself forming a secondary structure; these structures can further interfere with the movement of DNA polymerase.

leading dna strand

What is Lagging DNA Strand?

The lagging DNA strand synthesized in the opposite direction of replication of fork movement or the direction of 3′-5′. It synthesizes away from the fork.  Due to the opposite movement from the fork direction, the lagging DNA strand tends to be discontinuous and synthesis.

The lagging strands have fragments of DNA which are known as Okazaki fragments. The primase, which is responsible for adding an RNA primer, has to wait for the fork to open before putting in the primer. This makes Okazaki fragments.

The RNA primers are then removed and replaced with DNA, and the fragments of DNA are joined together by DNA ligase. Synthesis of the lagging strand is more complicated as compared to the leading strand due to the prevention of continuous synthesis by original DNA orientation.

As a consequence, the DNA polymerase on this strand is seen to “lag behind” the other strand. In prokaryotes, it wraps around the lagging strand. 

lagging dna strand

Main Differences Between Leading DNA Strand and Lagging Strand

  1. Leading DNA strand synthesized continuously, on the other hand, lagging DNA strand discontinuous synthesis in the form of Okazaki fragments.
  2. Leading DNA strand synthesized in the direction of movement of the fork, on the other hand, lagging DNA strand synthesized in the opposite direction from the movement of fork.
  3.  leading DNA strand synthesized in 5’ – 3’ direction on contrary lagging DNA strand synthesized in 3’ – 5’ direction.
  4. Leading DNA strand does not require RNA primer on the other hand lagging DNA strand required RNA primer.
  5. Helicase wraps around leading strands in Eukaryotes on the other hand wrapped around lagging DNA strands in prokaryotes.


  1. https://science.sciencemag.org/content/300/5623/1300.abstract
  2. https://www.embopress.org/doi/abs/10.1093/emboj/18.22.6561
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