The key difference between lagging and leading strand is that the synthesis of lagging strand is discontinuous and it occurs in the direction opposite to the growing replication fork while the synthesis of leading strand is continuous and it occurs in the same direction as the growing replication fork.
DNA replication is an important biological process that occurs in all living organisms. At the beginning of the replication process, double strands of the double helix unwind from each other and open up for the process. Then each strand acts as a template for the daughter strand. DNA replication takes place at the “replication fork” created by helicase enzyme, which is responsible for the breakdown of hydrogen bonds, connecting the two DNA strands together. The resulting single DNA strands serve as templates for the newly synthesized DNA strands called “lagging and leading strands”. Lagging strand synthesis is discontinuous while leading strand synthesis is continuous. Moreover, there are several other differences between lagging and leading strands as discussed in this article.
CONTENTS
1. Overview and Key Difference
2. What is Lagging Strand
3. What is Leading Strand
4. Similarities Between Lagging and Leading Strand
5. Side by Side Comparison – Lagging vs Leading Strand in Tabular Form
6. Summary
What is Lagging Strand?
Lagging strand is one of the two newly synthesized DNA strands in DNA replication. It occurs in 3’-5’ direction, which is the direction opposite to the growing replication fork. The synthesis of a new strand of replication DNA in lagging strand is by the creation “Okazaki fragments”, which are short segments of various length.
Figure 01: Lagging Strand and Leading Strand in DNA Replication
Moreover, an enzyme called DNA-ligase is responsible for joining these fragments together. Therefore, the activity of DNA-ligase enzyme is essential for the synthesis of the lagging strand.
What is Leading Strand?
Leading strand is the other newly created DNA strand that is replicated continuously, unlike the lagging strand. Therefore, the synthesis of this leading strand does not require DNA-ligase activity. Moreover, leading strand is in the 5’ to 3’ direction. It is this direction in which the replication fork is moving.
What are the Similarities Between Lagging and Leading Strand?
- Lagging and leading strand are two strands resulting from the DNA replication process.
- They are complementary to each other.
- However, the building blocks of each strand are deoxyribonucleotides.
- Also, the DNA polymerase enzyme catalyzes the synthesis of both strands.
- Moreover, the synthesis of both strands occurs at the same time.
What is the Difference Between Lagging and Leading Strand?
Lagging and leading strands are the two strands that result from the DNA replication process. In definition, lagging strand is one of the two strands produced in fragments during the DNA replication. In contrast, leading strand is the strand produced continuously during the DNA replication. Thus, this is the key difference between lagging and leading strand. Furthermore, lagging strand template is facing the 3’ to 5’ direction while leading strand template is facing the 5’ to 3’ direction. So, this is a significant difference between lagging and leading strand. Moreover, a further difference between lagging and leading strand is the synthesis process. The synthesis of lagging strand occurs discontinuously in fragments while the synthesis of leading strand occurs continuously during the replication process.
Additionally, the lagging strand synthesis occurs in fragments called Okazaki fragments, but not the leading strand synthesis. Also, one more difference between lagging and leading strand is the direction of synthesis. The direction of synthesis of lagging strand is 3’→5’. However, the direction of synthesis of leading strand is 5’→3’. Apart from that, lagging strand synthesis requires new primers, often to accommodate repetitive initiation events. However, DNA replication of the leading strand needs to be primed only once.
Below infographic summarizes the difference between lagging and leading strand in tabular form.
Summary – Lagging vs Leading Strand
DNA replication is an important process occurring in living organisms. It duplicates DNA molecules. The two new strands produced during the DNA replication are lagging strand and leading strand. In summarizing the difference between lagging and leading strand, the lagging strand is the strand produced discontinuously in Okazaki fragments in the 3’ – 5’ direction while leading strand is the strand produced continuously in the 5’- 3’ direction. Besides, lagging strand synthesis requires primase, DNA ligase other than DNA polymerase while leading strand synthesis only requires DNA polymerase.
Reference:
1. “DNA Replication.” Wikipedia, Wikimedia Foundation, 6 May 2019, Available here.
2. “DNA Replication: The Leading Strand and DNA Polymerase Activities.” Study.com, Available here.
Image Courtesy:
1. “DNA replication en” By LadyofHats Mariana Ruiz – Own work. Image renamed from File:DNA replication.svg, (Public Domain) via Commons Wikimedia