A LITTLE LIGHTBULB MOMENT
Genetics and molecular biology
Leading and lagging strands
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One strand sprints, the other gets stitched in fragments.
The idea behind the cue
Because DNA polymerase synthesizes only 5' to 3', one strand is made continuously toward the fork as the leading strand. The lagging strand is made discontinuously as Okazaki fragments.
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Short & simple
One strand sprints, the other gets stitched in fragments.
Acronym
LLO — Lazy Lobsters Orbit.
Story
At the fork, one worker lays a smooth sidewalk toward the finish line. The other has to lay little bricks backward as the road opens, then glue the bricks together.
Connect the pieces
- L (Lazy) → Leading: This strand is synthesized continuously toward the replication fork.
- L (Lobsters) → Lagging: This strand is synthesized discontinuously away from the fork.
- O (Orbit) → Okazaki: These are the short DNA fragments made on the lagging strand.
- Lazy · Leading: This strand is synthesized continuously toward the replication fork.
- Lobsters · Lagging: This strand is synthesized discontinuously away from the fork.
- Orbit · Okazaki: These are the short DNA fragments made on the lagging strand.
Know the limits
Both strands still require primase and ligase; the terms describe synthesis at a moving replication fork.
Further reading · OpenStax science textbooks ↗Check your understanding
Why is the lagging strand synthesized in fragments?
A. Helicase works only on one strand
B. RNA polymerase cannot copy DNA continuously
C. Ligase can only join single nucleotides
D. DNA polymerase only adds nucleotides 5' to 3'
Reveal explanation
DNA polymerase only adds nucleotides 5' to 3'
DNA polymerase can extend only in the 5' to 3' direction, forcing discontinuous synthesis on one strand.