Leading vs Lagging DNA Strand: Difference and Comparison

For the continuation of life on earth, living organisms give birth to offspring that look like them; this characteristic of passing genes is only seen in living beings.


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Dera fuel requirements of passing these genes, the major requirement is DNA. DNA stands for deoxyribonucleic acid; It is mainly responsible for the 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 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. The replication of strands goes in 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 with a single DNA strand.

DNA is read by DNA polymerase in a 3’-5’ or 5’-3’ direction. These are commonly classified as leading DNA strands and lagging DNA strands; both are completely different and opposite to each other, making reading sometimes difficult. 

Key Takeaways

  1. The leading strand undergoes continuous replication, while the lagging strand undergoes discontinuous replication.
  2. DNA polymerase III synthesizes the leading strand, while DNA polymerase I synthesize the lagging strand.
  3. The leading strand has fewer primers than the lagging strand, requiring multiple primers for the Okazaki fragments to be synthesized.

Leading DNA Strand vs. Lagging DNA

The Leading Strand replicates continuously in the 5’3 direction of the movement of the replication fork. The leading strand does not require RNA primer. The lagging strand replicates discontinuously in the 3’5 direction opposite to the movement of the replication fork. It requires RNA primer.

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 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 the Leading DNA Strand?

The leading DNA strand is the strength that 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, making 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 rotates. This process results in a build-up of twists in the DNA ahead.    

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

leading dna strand

What is a 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 synthesized.

The lagging strands have fragments of DNA which are known as Okazaki fragments. The primase, 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 than the leading strand due to the prevention of continuous synthesis by original DNA orientation.

Consequently, the DNA polymerase on this strand is seen to “lag” 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 strands to synthesize continuously; on the other hand, lagging DNA strands discontinue synthesis in Okazaki fragments.
  2. Leading DNA strands are synthesized in the direction of movement of the fork; on the other hand, lagging DNA strands are synthesized in the opposite direction from the movement of the fork.
  3.  Leading DNA strand synthesized in a 5’ – 3’ direction. On the contrary, lagging DNA strands are synthesized in a 3’ – 5’ direction.
  4. The leading DNA strand does not require RNA primer. On the other hand, lagging DNA strands require 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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