• 14 parts
  • Checked September 2026

DNA Replication Diagram Labeled

One replication fork, with every strand and enzyme numbered.

DNA Replication Diagram Labeled

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1 2 3 4 5 6 7 8 9 10 11 12 13 14
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Write the name of each numbered part.Answer key

  1. Replication fork
  2. Template strand (parent strand)
  3. Leading strand
  4. Lagging strand
  5. Okazaki fragment
  6. RNA primer
  7. Helicase
  8. Topoisomerase
  9. Single-strand binding proteins
  10. Primase
  11. DNA polymerase III
  12. Sliding clamp
  13. DNA polymerase I
  14. DNA ligase

Drawn for this site by script, 2026-09-26. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Before the copy: the structure of DNA

All 14 parts on the diagram

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Simple: 7 main parts 7

  1. Replication fork Where the parent helix opens into two template strands.
  2. Template strand (parent strand) An old strand that each new strand is copied from.
  3. Leading strand Made continuously, towards the fork.
  4. Lagging strand Made in short pieces, away from the fork.
  5. Helicase Unzips the helix by breaking the hydrogen bonds.
  6. DNA polymerase III The main enzyme adding nucleotides, 5' to 3'.
  7. DNA ligase Seals the gap between fragments.

Strands: 5 1

  1. Okazaki fragment A short stretch of the lagging strand, later joined up.

Enzymes and primers: 9 6

  1. RNA primer A short RNA start that DNA polymerase extends.
  2. Topoisomerase Relieves over-winding ahead of the fork with temporary nicks.
  3. Single-strand binding proteins Coat the single strands so they do not rejoin.
  4. Primase Makes each RNA primer.
  5. Sliding clamp Holds DNA polymerase on the strand.
  6. DNA polymerase I Removes RNA primers and fills in DNA.

How this list was compiled: Read 2026-09-26. OpenStax Biology 2e, 14.4 DNA Replication in Prokaryotes, https://openstax.org/books/biology-2e/pages/14-4-dna-replication-in-prokaryotes : helicase separates the strands at the replication fork; single-strand binding proteins stop them rewinding; topoisomerase prevents over-winding ahead of the fork with temporary nicks; primase makes an RNA primer; DNA polymerase III adds nucleotides 5' to 3', held by the sliding clamp; the leading strand is made continuously towards the fork, the lagging strand in Okazaki fragments; DNA polymerase I removes the primers and replaces them with DNA; DNA ligase seals the gaps. Wikipedia, DNA replication, https://en.wikipedia.org/wiki/DNA_replication : replication fork, template, helicase, topoisomerase, single-strand binding proteins, primase and primers, polymerases, sliding clamp, leading and lagging strands, Okazaki fragments, ligase. Licence: own work

The drawing: Drawn for this site by script, 2026-09-26. Licence: own work

How it works

This DNA replication diagram labeled part by part shows one replication fork in a bacterium. Old strands are grey, new ones green and RNA primers yellow. The simple set asks the 7 main parts; the full set adds every enzyme.

Read the full guide

Opening the helix

Helicase unzips the double helix at the replication fork. Topoisomerase, ahead of it, relieves the over-winding this causes, and single-strand binding proteins coat the opened template strands so they do not rejoin.

Leading and lagging strands

DNA polymerase III adds nucleotides only in the 5' to 3' direction. On the leading strand it works continuously towards the fork, held on by the sliding clamp. The lagging strand is made away from the fork in Okazaki fragments, each begun from an RNA primer.

  • Later, DNA polymerase I swaps each RNA primer for DNA, and DNA ligase seals the gaps between the fragments.

Questions and answers

Why is the lagging strand made in pieces?

DNA polymerase can only add nucleotides in the 5' to 3' direction, and the two strands run in opposite directions. On one template it can follow the fork; on the other it must work away from it, one Okazaki fragment at a time.

What does primase do in DNA replication?

It makes the short RNA primer that DNA polymerase needs as a starting point, once on the leading strand and again for every Okazaki fragment.

What does helicase do?

It separates the two strands at the replication fork by breaking the hydrogen bonds between the base pairs.

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