# Replication Bubble --- A **replication bubble** is the structure that forms during [[DNA replication]] as DNA is unzipped by [[DNA replication#Step 1 Unzipping|DNA helicase]]. The unzipping begins at the [[DNA replication|origin of replication]] and continues outward in both directions. The Y-like formations on either end of the bubble where the actual unzipping action takes place are called the **replication forks**. DNA helicase and the replication forks move along down the strands until they merge with another bubble down the line, come to the end of the strand, or, in the case of [[#Replication Bubble in Prokaryotes|prokaryotic replication bubbles]], merge with itself. ![[replication bubble.png]] ## Replication Bubbles in Eukaryotes Eukaryotes have a a lot of DNA to get through, so if there was only one bubble it would take forever! So, there are many different [[DNA replication|points of origin]] that all move out simultaneously Even so, human cells take over 18 hours to copy the whole genome and divide the cell. (Compare this with bacteria, who can reproduce in about 20 minutes, or yeast that takes two hours.) ## Replication Bubble in Prokaryotes Prokaryotes have [[prokaryotic DNA|circular DNA]], so they only use one origin of replication and it just zips right off. ![[bacterial replication bubble.png]] ___