Replication Bubble: Definition & Overview

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  • 0:00 DNA Review
  • 1:07 Replication Bubble
  • 1:55 Stabilization
  • 2:29 Replication Bubble Elongation
  • 3:23 Lesson Summary
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Lesson Transcript
Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

A replication bubble is the setting for DNA replication. In this lesson, we will review DNA, then find out why replication bubbles are called a bubble, what stabilizes them and how DNA polymerase finishes up.

DNA Structure

What do bubbles have to do with DNA replication? Is it taking a bath before dividing in two? Hm, let's review DNA structure before we find out. We can remember that DNA, or deoxyribonucleic acid, the blueprints to all life, is made from two chains of nucleotides that wind up together to form a double helix. A double helix looks like a twisted rope ladder. The rungs of the ladder are formed by pairing between nucleotide bases from each of the DNA strands.

A DNA double helix showing the complementary base pairs

Each base has a partner base that it always binds with (adenine with thymine and guanine with cytosine). Specific pairing means that the strands are perfectly complementary. Each strand is basically the same information, but they are mirror images that fit together like two strips of velcro.

Every cell in our bodies needs a full copy of the genome (except for sperm and egg cells, but they are special). This means that each time a cell divides, it needs to copy the genome. It is convenient that the DNA strands are complementary, because each strand can be used as a template during replication.

Replication Bubble

DNA replication is when one strand of DNA is split down the middle and forms two, identical copies. However, in order for this to occur, the strands of DNA must first be separated. An enzyme called helicase is used to separate these two strands.

Like a zipper that has unzipped in the middle, the separated DNA strands form a little open pucker. This is the replication bubble. A replication bubble is an unwound and open region of a DNA helix where DNA replication occurs. Helicase unwinds only a small section of the DNA at a time in a place called the origin of replication. In eukaryotes, there are several origins of replication on each chromosome. The two sides of each bubble (where it goes from zipped to unzipped) are called replication forks.

Stabilizing the Bubble

After the replication bubble is formed, there are special proteins called single-strand binding proteins that bind to the individual strands and prevent the helix from winding back up again.

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